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Environmental Issues Introduction

Human population size has grown enormously over the last hundred years with increase in demand for food, water, home, electricity, roads, automobiles, and numerous other commodities; and exerting tremendous pressure on our natural resources, along with contributing to the pollution of air, water, and soil. The need is to check the degradation and depletion of natural resources and pollution without halting the process of development.

Any undesirable change of the physical, chemical, or biological characteristics in the atmosphere, lithosphere, and hydrosphere which is harmful to man directly or indirectly is called pollution.

Kinds Of Pollution

• On the basis of part of environment where it occurs most
  • Air pollution
  • Water pollution
  • Soil pollution
• On the basis of origin
  • Natural: Examples are volcanic eruptions; release of CH4 by paddy fields and cattle; release of CO by plants and animals; emission of natural gas, O3, nitrogen oxides, cosmic rays, and UVrays; etc.
  • Anthropogenic (man-made): Examples are burning of fossil fuels, deforestation, mining, sew- age, industrial effluent, pesticides, fertilizers, etc.
• On the basis of physical nature of pollutants
  • Gaseous pollution
  • Dust pollution
  • Thermal pollution
  • Noise pollution
  • Radioactive pollution, etc.

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Pollutants

• Non-biodegradable: DDT, BHC, waste plastic bottles, polyethylene bags, used soft drink cans, etc.
• Biodegradable: Sewage, market garbage, livestock wastes, etc.
• Primary pollutant: CO and DDT.
• Secondary pollutant: Nitrogen oxides and hydrocarbons react photochemically to produce peroxyacyl nitrates and O3.
• Qualitative: Insecticides, weedicides, and fungicides.
• Quantitative: CO, CO2, NO, and NO2.

Air Pollution

Fifty-two percent of air pollution is caused by CO, 18% by SO2, 12% by hydrocarbons, 10% by particulates, 6% by nitrogen ox- ides, and 2% by the remaining matter.

Primary Air Pollutants

• Particulate matter
  • Settleable: Diameter is 10 mm and settles out in less than a day.
  • Suspended: Diameter is 1 mm and can remain suspended for weeks. Examples are aerosol, dust, mist, and fly ash.
    Suspended particulate matter (SPM) (particularly of size 2.5 g or less) in troposphere causes and aggravates human respiratory illness such as asthma, chronic bronchitis irritation, and premature death. SPM in stratosphere alters the radiation and thermal budgets of the atmosphere, lowering the temperature at the earth’s surface.
• Carbon monooxide: It is a product of incomplete combustion of fossil fuels. 50% emissions are from automobiles. It produces COHb (carboxyhemoglobin) and reduces oxygen carrying capacity of blood, resulting in giddiness, decreased vision, headache, cardio- vascular malfunction, and asphyxia.
• Hydrocarbons (HCs) or volatile organic carbons (VOCs): These are produced naturally (c.g., CH4) or due to incomplete combustion. Benzene and HCHO are carcinogenic and cause irritation of eyes and mucous membrane and bronchial constriction. HCHO leads to indoor pollution.
• SO2: It is produced during the combustion of sulfur containing fossil fuels and smelting of ore from oil refineries. It causes eye irritation, severe respiratory problems, inhibits ETS in plants, and is also responsible for classical smog (London smog or sulfurous smog) and stone cancer.
• Nitrogen oxides (NO): These are mainly produced during the combustion of fossil fuels at high temperature in automobile engines. Nitrogen oxides cause brown air that leads to heart and lung problems.

Secondary Air Pollutants

Secondary air pollutants are formed through reaction between primary pollutants and often are more toxic.

• Photochemical smog (Los Angeles smog): It is a pollutant and is related to smog and fog.
• Acid rain: Sulfur dioxide and nitrogen oxide cause pollution by increasing acidity. Sulfuric acid is present in acid rain.

Air Pollution and Its Control

There are several ways of removing particulate matter; the most widely used of which is the electrostatic precipitator. It can remove over 99% particulate matter (PM) present in the exhaust from a thermal power plant. It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons. These electrons attach to dust particles giving them a net negative charge.

The collecting plates are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust to fall. A scrubber can remove gases such as sulfur dioxide. In a scrubber, the exhaust is passed through a spray of water or lime.

Recently, we have realized the dangers of particulate matter that are very-very small and are not removed by these precipitators. According to Central Pollution Control Board (CPCB), particulates of size 2.5 μm or less in diameter (PM 2.5) are responsible for causing the greatest harm to human health. These fine particulates can be inhaled deep into the lungs and can cause breathing and respiratory symptoms, irritation, inflammations and damage to the lungs, and premature deaths.

Catalytic converter has expensive metals such as platinum and palladium and can convert NO, to nitrogen and CO to CO2.

Controlling Vehicular Air Pollution: A Case Study of Delhi

Delhi leads the country in its levels of air-pollution-it has more cars than the states of Gujarat and West Bengal put together. In the 1990’s, Delhi ranked fourth among the 41 most polluted cities of the world. Air pollution problems in Delhi became so serious that a public interest litigation (PIL) was filed in the Supreme Court of India.

After being censured, the government was asked to take, within a specified time period, appropriate measures, including switching over the entire fleet of public transport, i.e., buses, from diesel to compressed natural gas (CNG). All the buses of Delhi were converted to run on CNG by the end of 2002. CNG has the following advantages:

• It burns most efficiently.
• It is cheaper than petrol or diesel.
• It cannot be siphoned off by thieves and adulterated like petrol or diesel.
• The main problem that government faced was the difficulty of laying down pipelines to deliver CNG through distribution points/pumps and ensuring uninterrupted supply.
• The use of unleaded petrol, low-sulfur petrol and diesel, and catalytic converters in vehicles; the application of stringent pollution-level norms for vehicles; etc., are the steps taken to reduce pollution.
• Stringent norms for fuels were given in the new auto fuel policy for steadily reducing the sulfur and aromatics content in petrol and diesel fuels. Euro II norms, for example, stipulate that sulfur be controlled at 350 parts-per-million (ppm) in diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42% of the concerned fuel. The goal, according to the roadmap prepared by the Indian Government, is to reduce sulfur to 50 ppm in petrol and diesel and bring down the level to 35%. Vehicle engines will also need to be upgraded.
• The Bharat Stage II (equivalent to Euro-II norms), which is currently in place in Delhi, Mumbai, Kolkata, Chennai, Bangalore, Hyderabad, Ahmadabad, Pune, Surat, Kanpur, and Agra, is applicable to all automobiles throughout the country since April 1, 2005.
• All automobiles and fuels petrol and diesel-were to have met the Euro-3 emission specifications in these 11 cities from April 1, 2005, and the Euro-4 norms by April 1, 2010. The rest of the country has Euro-3 emission norm compliant automobiles and fuels since 2010.
• A substantial fall in CO2 and SO2 levels has been found in Delhi between 1997 and 2005.

Water Pollution

Water pollution is the adverse change in the composition or condition of water such that it becomes less suitable for the purposes for which it would be suitable in its natural state.

Sources

• Point sources (e.g., sewage outlet of a municipal area or effluent outlet of a factory)
• Non-point sources (e.g., city storm water flow and agriculture runoff)

Pollutants

Various types of pollutants are as follows:

• Biological
• Chemical
• Physical
  • Household detergents
  • Domestic sewage
  • Industrial wastes
  • Offshore oil drilling
  • Thermal power plants
  • Pollution of detergents in water: It prevents the decomposition of organic compounds as it forms a thin film around them due to its low surface tension (surfactant nature). This results in the ac- cumulation of organic substances in water. There- fore, detergents are also called builders.

Effects

• Decreasing of dissolved O2 (DO or dissolved oxygen) content of water bodies.
• Higher biological oxygen demand (BOD): BOD is the amount of O2 in milligrams required to decompose organic matter present in 1 L water kept at temperature of 20°C for 5 days. If it is 4090 mg/L, then water is heavily polluted.
• COD (chemical oxygen demand): It indicates total O2 requirement of all O, consuming pollutant materials present in water. Its value is higher than BOD.
• Annelid worm Tubifex and some insect larvae act as indicator species for polluted waters.
• Persistent pesticides (e.g., DDT) and mercury pass into the food chain. Their increase in amount per unit weight of organism with the rise in trophic level is called biological magnification.
• Biomagnification of DDT causes hemorrhage, softening of brain, liver cirrhosis, hypotension, etc.

• Eutrophication is increase in the amount of nutrients in water due to detergents, pesticides, etc. It leads to organic loading, depletion of O2, etc.
• Minamata disease is caused due to mercury in water.

A Case Study of Integrated Waste Water Treatment

• Waste water including sewage can be treated in an integrated manner. An example of such an initiative is the town of Arcata (California).
• The town’s people created an integrated waste water treatment process within a natural system in collaboration with Humboldt State University.
• The cleaning occurs in two stages:
  • The conventional sedimentation, filtering, and chlorine treatments are given. But after this stage, dissolved heavy metals still remain.
  • Biologists developed a series of six connected marshes over 60 ha of marshland. Appropriate organisms were seeded into this area, which neutralize, absorb, and assimilate the pollutants. Hence, as the water flows through the marshes, it gets purified naturally; marshes also constitute a sanctuary.
• Friends of the Arcata Marsh (FOAM) are responsible for the upkeep and safeguarding of this wonderful project.
• Ecological sanitation is a sustainable system for handling human excreta using dry composting toilets. This is a practical, hygienic, efficient, and cost-effective solution by which human excreta can be recycled into a resource (as natural fertilizer), which reduces the need for chemical fertilizers. There are working “ecosan” toilets in many areas of Kerala and Sri Lanka.

Solid Waste

• Solid wastes refer to everything that goes out in trash.
• Sanitary landfills were adopted as the substitute for open-burning dumps wherein sanitary landfill wastes are dumped in a depression or trench after compaction and covered with dirt every day.
• But these sites are getting filled too and the seepage of chemicals, etc., from these landfills pollutes underground water resources.
• Anthropogenic waste is categorized into three types: (a) bio-degradable, (b) recyclable, and (e) non-biodegradable.
• Polyblend, a fine powder of recycled modified plastic, was developed by the company owned by Ahmed Khan in Bangalore. This mixture is mixed with bitumen, which is used to lay roads. Blends of polyblend and bitumen, when used to lay roads, enhanced bitumen’s water repellant properties and helped to increase road life by a factor of three.
• The use of incinerators is crucial for the disposal of hospital waste.
• Irreparable computers and other electronic goods are known as electronic wastes (e-wastes). e-wastes are buried in landfills or incinerated. Over half of the e-wastes generated in the developed world are exported.
• Developing countries such as China, India, and Pakistan import over half of the e-waste generated by developed countries for the recovery of metals such as copper, iron, silicon, nickel, and gold.
• Recycling is the only solution for the treatment of e-wastes, provided it is carried out in an environment-friendly manner.

Soil Pollution

• Soil pollution is the alteration in soil caused by the removal or addition of substances and factors which decrease its productivity and the quality of plants and ground water.
• Non-biodegradable materials such as polyethylene carry bags, waste plastic sheets, and bottles persist in soil for long periods.
• Hospital wastes also cause soil pollution.
• Excessive use of fertilizers causes soil deterioration and decreases the natural microflora.
• Mine dust destroys top soil and contaminates the area with toxic metals and chemicals.
• Recycling of solid wastes, burning of waste, utilizing heat to warm residential units, and generation of electricity is the best way to control soil pollution.
• Incineration (burning in the presence of O2 at 1200°C) and pyrolysis (combustion in the absence of O2 at 1650°C) methods can be used to eliminate solid wastes.
• Soil erosion and overgrazing are negative pollution.

Case Study of Organic Farming

Integrated organic farming is a cyclical, zero-waste procedure, where waste products from one process are cycled as nutrients for other processes. This allows the maximum utilization of resources and increases the efficiency of production. Ramesh Chandra Dagar, a farmer in Sonipat, Haryana, is doing just this. He includes bee-keeping, dairy management, water harvesting, composting, and agriculture in a chain of processes, which support each other and allow an extremely economical and sustainable venture.

There is no need to use chemical fertilizers for crops, as cattle excreta (dung) are used as manure. Crop waste is used to create compost, which can be used as a natural fertilizer or can be used to generate natural gas for satisfying the energy needs of the farm. Enthusiastic about spreading information and help on the practice of integrated organic farming, Dagar has created the Haryana Kisan Welfare Club, with a cur- rent membership of 5000 farmers.

Global Environment Change

CO2, CH4, N2O, and CFCs are radiatively active gases (also called greenhouse gases). The increased amounts of these gases in atmosphere are affecting the global climate. This phenomenon is known as global climatic change.

Greenhouse Gases and Global Warming

• The term “greenhouse effect” was coined by Arrhenius.
• Greenhouse gases trap the long-wave radiations. A part of this energy is re-radiated back to the surface of the earth. The downward flux of long-wave radiations by greenhouse gases is called greenhouse flux.
• The phenomenon of keeping the earth warm due to the presence of certain radiatively active gases in the atmosphere is called greenhouse effect, without which the average temperature of the earth would have been -18°C-20°C rather than the present average of 15°C.

• The excessive increase in the concentrations of these gases in the atmosphere would retain more and more infrared radiation, resulting in enhanced greenhouse effect.
• CFC is the most effective greenhouse gas (effectiveness is 14,000 times more than CO2).

Effects of Greenhouse Gases

• CO2 fertilization effect: An increase in the atmospheric concentration of CO2 increases the productivity of C3 plants and decreases the rate of transpiration due to partial stomatal closure.
• The possible effects of global warming are as follows:
  • Increasing of global temperature (increased 0.6°C, most of it during the last three decades) and more extreme climatic conditions (El Nino effect).
  • Warming of troposphere and cooling of stratosphere and thermosphere.
  • Melting of ice caps.
  • Rising of sea level; changes in rainfall pattern.
  • Global warming will push tropics into temperate areas and temperate areas towards pole (shifting of climatic zones) and higher altitudes in mountains resulting in changed species distribution.
• Control measures: Reduced deforestation, cutting down use of fossil fuels, planting trees, and slowing down population growth.
• Ozone depletion
  • Ozone layer is present in stratosphere at an altitude of 23-25 km (conc. 0.3 ppm). It acts as shield against UV radiation.
  • A large hole has appeared in the ozone shield over Antarctica and a smaller one over North Pole (discovered by Farman in 1985).
  • Ozone is commonly called chemical weed.
  • CFC, CH4, CCl4, halogens, and N2O cause the destruction of O3. These are ozone depleting substances (ODS).
  • CFCs are the most damaging. These release Cl atoms in the stratosphere which destroy O3.
  • Thinning of the ozone layer results in an increase in the UV-B radiation.
  • UV-B causes snow blindness.
  • Nowadays, CFCs are being replaced by hydro- fluorocarbons (HFCS) and hydrochlorofluorocarbons (HCIFCs).

Radioactive Wastes

• The use of nuclear energy has two very serious inherent problems. The first is accidental leakage, as occurred in the Three Mile Island and Chernobyl incidents and the second is safe disposal of radioactive wastes.
• It causes mutations to occur at a very high rate. At high doses, nuclear radiation is lethal but at lower doses, it creates various disorders, the most frequent of all being cancer.
• It has been recommended that the storage of nuclear waste, after sufficient pre-treatment, should be done in suitably shielded containers buried within the rocks, about 500 m deep below the earth’s surface.

Degradation By Improper Resource Utilities And Maintenance

Soil Erosion and Desertification

• The fertile top-soil formation takes centuries. But it can be removed very easily due to human activities such as over-cultivation, unrestricted grazing, deforestation, and poor irrigation practices, resulting in arid patches of land. These barren patches extend and meet over time and create a desert.
• Desertification is becoming a major problem, particularly due to increased urbanization.

Water-logging and Soil Salinity

Water Logging

Water logging means a kind of physiological dry soil in which water is present but not available from plants.

Soil Salination

Soil salination is increase in the concentration of salts in a soil. It may develop due to the following reasons:

• The formation of soil from rocks having salts.
• Poor drainage and elevated water table.
• Nearness to sea.
• Continuous addition of fertilizers, etc.

Water logging and soil salinity are some of the problems that have come in the wake of the Green Revolution.

Noise Pollution

Noise pollution is that form of sound energy which is not appreciated by human ears, i.e., it is undesired high level of sound.

• The frequency of sound is measured in hertz (Hz) while the unit of sound is decibel (dB).
• Moderate conversation = 60 dB
  Loud conversation = 70 dB
  Scooter = 30 de
  Truck/bus = 90 dB
  Jet aeroplane 150 dB
  Rocket = 180 dB
• Zone-wise permissible ambient noise levels are given in Table 16.2 (according to the Central Pollution Control Board).
• Green Muller scheme: It is growing of trees and shrubs in rows around the noisy area and road-sides to reduce intensity.

Effects of Noise Pollution

• A regular exposure to sound of 80 dB reduces hearing by 15 dB in 10 years.
• A sudden high intensity noise can damage ear drums.
• Noise pollution leads to anxiety, stress, insomnia, emotional disturbance, and hypertension.

Deforestation

• Deforestation is the conversion of forested areas to non-forested ones. It is estimated that almost 40% forests have been lost in the tropics, compared to only 1% in the temperate region.
• At the beginning of the 20th century, forests covered about 30% of the land of India. By the end of the century, it shrunk to 19.4%, whereas the National Forest Policy (1988) of India has recommended 33% forest cover for the plains and 67% for the hills.
• Trees are axed for timber, firewood, cattle ranching, and several other purposes. Slash-and-burn agriculture, commonly called as Jhum cultivation in the north-eastern states of India, has also contributed to deforestation.
• One of the major effects is enhanced carbon dioxide concentration in the atmosphere. It also causes loss of biodiversity due to habitat destruction, disturbs hydrologic cycle, causes soil erosion, and may lead to desertification in extreme cases.
• Reforestation is the process of restoring a forest. It may also occur naturally in a deforested area.

Case Study of People’s Participation in Conservation of Forests

• A Bishnoi woman of Khejarli village, Jodhpur, Rajasthan, named Amrita Devi showed exemplary courage by hugging a tree.
• The Amrita Devi Bishnoi Wildlife Protection Award is given to individuals or communities from rural areas that have shown extraordinary courage and dedication in protecting wildlife.
• Chipko Movement: It is the movement which was initially meant for protecting trees and not for the preservation of environment including habitat and wildlife. The Chipko Movement was born in March, 1973, in Gopeshwar in Chamoli district. The movement has two leaders: Chandi Prasad Bhatt of Gopeshwar and Sunder Lal Bahugana of Silyara in Tehri region. A similar movement was undertaken by Pandurang Hedge in the South. It is known as the Appiko Movement.
• The Government of India in 1980’s introduced the concept of joint forest management (JFM).

 

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: Euro 2 norms are framed to reduce the content of CO and aromatic compounds from fuels.

Reason: These compounds lead to reduced visibility and carboxyhemoglobin formation.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 2. Assertion: Sewage discharge in a water body causes eutrophication.

Reason: This increases the organic content in water body and, hence, the growth of algal blooms.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 3. Assertion: Biomagnification of DDT can enhance the de- cline in bird population.

Reason: DDT causes thinning of egg shell and their premature breaking by disturbing calcium metabolism.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 4. Assertion: Ecological sanitation is a sustainable system for handling human excreta.

Reason: It is a practical and hygienic method of using dry composting toilets.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 5. Assertion: El Nino is a climatic change which causes deleterious environmental changes.

Reason: Increased tropospheric ozone due to El Nino causes shift of climatic regions.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Biodiversity And Conservation Introduction

The occurrence of different types of genes, gene pools, species, habitats, and ecosystem in a particular place and various parts of the earth is called biodiversity (term popularized by Edward Wilson).

Currently, the number of predescribed species of all plants and animals is slightly more than 1.5 million.

Robed May estimated global species diversity at about 7 million (means only 22% of total diversity has been recorded so far).

Estimates Of Species Number On Earth And In India

• Of the total estimate, more than 70% are animals while plants (including fungi) comprise no more than 22%. The most species-rich taxonomic group is insect (70% of animals).
• The number of fungal species in the world is more than the combined total of fishes, amphibians, reptiles, and mammals.
• No estimations are available for prokaryotes as consell giventional taxonomic methods are not suitable, and many of them are not culturable. We may accept bio-chemical/molecular criteria of estimation of diversity in this group.
• India has 2.4% of world’s land, with 8.1% of global diversity. So, India is among 12 mega-diverse countries.
• Nearly 45,000 plant species and twice as many animal species have been recorded from India.
• Applying May’s method, more than 1,00,000 plant and 3,00,000 animals species are yet to be discovered and described.
• Approximately 15,000 new species are discovered every year.

Read and Learn More NEET Biology Notes

Levels Of Biodiversity

There are three types of biodiversity:

• Genetic diversity
  • It is a measure of variety in genetic information contained in the organism, e.g., 10-150 genes in virus, 450-700 genes in Mycoplasma, and 32,000-50,000 genes in Oryza sativa.
  • It enables a population to adapt to its environment, e.g., Rauwolfia vomitoria in Himalayan ranges.
  • It helps in the formation of ecotype.
  • It plays a key role in the process of speciation. It maintains diversity at the community level.
• Species diversity
  • It is the variety of species within a region, e.g., Western Ghats are more diverse than Eastern Ghats.
  • Species richness is the number of species present within a unit area.
  • Species diversity is the product of species richness and species evenness.
  • Maximum/taxonomic diversity occurs where the species of taxonomically different groups occur in almost equal abundance.
  • Species evenness is the proportionate number of individuals of different species.
• Community or ecosystem diversity

It is of three types (Whittaker):

• • a-diversity (within community diversity): It is also called local diversity. It is diversity within a community.
  • B-diversity (between community diversity): It is calculated by dividing y by a diversity. It is diversity between two communities.
  • y-diversity: It is also called regional diversity. It represents the total richness of species in all the habitats found within a region, geographical area, or landscape. For example, India is more diverse than Norway.

Patterns of Biodiversity

• The degree of biodiversity shows two master gradients: latitudinal and altitudinal.
• Biodiversity increases from high to low latitudes, i.e., from the poles to the equator.
• Biodiversity is minimum in arctic, moderate in temperate, and maximum in tropical regions. With very few exceptions, tropics (latitudinal range of 23.5° N to 23.5° S) harbor more species than temperate or polar areas. Colombia located near the equator has nearly 1,400 species of birds while New York at 41° N has 105 species and Greenland at 71° N has only 56 species.
• India with much of its land area in the tropical latitudes has more than 1200 species of birds. A forest in a tropical region such as Equador has up to 10 times as many species of vascular plants as in a forest of equal area in a temperate region such as the Midwest of the USA. The largely tropical Amazonian rain forest in South America has the greatest biodiversity on the earth.
• It is home to more than 40,000 species of plants, 3000 of fishes, 1300 species of birds, 427 species of mammals, 427 species of amphibians, 378 species of reptiles, and more than 1,25,000 species of invertebrates. Scientists estimate that in these rain forests, there might be at least 2 million insect species waiting to be discovered and named.
• Tropics show greater diversity because of the following reasons:
  • Speciation is generally a function of time. Unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and, thus, had a long evolutionary time for species diversification,
  • Tropical environments are less seasonal, are relatively more constant and predictable, can promote niche specialization, and lead to a greater species diversity.
  • Species-area relationships: Alexander Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit. In fact, the relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola.
    The relationship is a straight line described by the equationlog S = log C + Z log Awhere S is species richness, A is area, Z is the slope of the line (regression coefficient), and C is the Y-intercept.

• Ecologists have discovered that the value of Z lies in the range of 0.1 to 0.2, regardless of the taxonomic group or region. If we analyze the species area relationships among very large areas such as the entire continents, the slope of the line will be much steeper (Z values in the range of 0.6 to 1.2). For frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents, the slope is found to be 1.15.
• Diversity decreases from lower to higher altitudes on a mountain, i.e., it is maximum at the base.
• Conditions favoring growth do not induce biodiversity or speciation; it is called the paradox of enrichment.

Importance of Species Diversity to the Ecosystem

Community with more species is more stable. Stable community should not show too much variation in productivity per year and must be resistant or resilient to occasional disturbances by natural or anthropogenic agencies and alien species. Ecosystem health/balance will be severely affected if species. extinction (particularly key stone) occurs.

Biodiversity Conservation

• Narrowly utilitarian aspect:
  • Pinus, Abies, and Boswellia are major sources of paper.
  • Pine resin is obtained from Pinus while damar is obtained from Shorea robusta.
  • Gums: Kuteera gum (Stericulia urens), Bengal kino gum (Butea monosperma), salai (Boswellia serrata), dhaora (Anogeissus latifolia), gum Arabic (Acacia senegal), etc.
  • Tannin sources: Uncaria (leaves and young branches), Acacia (bark), Juglans (bark), and Caesalpinia (wood and fruits).
  • Important dyes: Cutch/kattha (heartwood of Acacia catechu), henna (leaves of Lawsonia inermis), and haematoxylon (heartwood of Haematoxylon campechianum).
  • Plants can also be used to manufacture innumerable synthetic products called botanochemicals.

• Broadly utilitarian aspect: Ecosystem services are important.
• Ethical aspect: Every species has an intrinsic value.
• Loss of Biodiversity IUCN Red List documents the extinctions of 784 species (including 338 vertebrates, 359 invertebrates, and 87 plants) in the last 500 years.
• Some recent extinctions: Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller’s sea cow (Russia), and three subspecies (Bali, Javan, and Caspian) of tiger.
• 27 species have disappeared in the last 20 years.
• Presently, 12% birds species, 23% of all mammals, 32% of all amphibians, and 31% of all gymnosperms in the world are facing the threat of extinction (more than 15,500 species).
• The sixth extinction is 100-1000 times faster.
• This may lead to decline in plant production, lowered resistance, and increased variability in ecosystem processes, e.g., pest and disease cycle.

Causes of Biodiversity Losses

• Important factors that cause loss of biodiversity are habitat loss, habitat fragmentation, disturbance, over exploitation, pollution, exotic species, intensive agriculture, and forestry (growing only exploitable forest plants).
• Habitat destruction or loss is the primary cause of the loss of biodiversity (tropical rain forests were once covering 14% while now they cover 6% only), Amazon valley.
• Habitat fragmentation reduces the core area and in- creases the edge area.
• Dodo of Mauritius, messenger pigeon, Steller’s sea cow, and Tasmanian wolf have become extinct due to overexploitation. Heath hen disappeared due to hunting and habitat destruction.
• Exotic (alien) species becoming invasive is considered another potent factor for the extinction of species.
• Examples of some exotic species: Water hyacinth (Eichhornia crassipes), Lantana (Lantana camera), congress grass (Parthenium hysterophorus), Nile perch, Eupatorium (Eupatorium cdoratum), and African catfish (Clarias gariepinus).
• Coextinction: For example, coevolved species.

Susceptibility to Extinction

Species more susceptible to extinction have the following population characteristics:

• Large body size (e.g., rhinoceros and lion)
• Small population size and low reproductive rate (e.g., giant panda and blue whale)
• High trophic level in food chain (e.g., bald eagle and Bengal tiger)
• Fixed habitat and migratory routes (e.g., whooping crane and blue whale)

IUCN Red List

• World Conservation Union (WCU) which was formerly known as International Union for the Conservation of Nature and Natural Resources (IUCN), headquarter at Mc-den, Switzerland, has recognized eight Red List categories of species. They are extinct, extinct in wild, critically endangered, endangered, vulnerable, lower risk, data deficient, and not evaluated.
• Critically endangered, endangered, and vulnerable species are called threatened species.
• Rare species have a small population and these are nei- ther vulnerable nor endangered but are at risk.
• A taxon is critically endangered when it is facing an extremely high risk of extinction in the wild in the immediate future.
• A taxon is endangered when it is facing a high risk of extinction in the wild in the near future.
• A taxon is vulnerable when it is facing a high risk of extinction in the wild in the medium term future.

Conservation of Biodiversity

There are two types of conservation strategies: in situ (on site) and ex situ (off site).

In situ Conservation

• Examples of protected areas: National parks, wildlife sanctuaries, and biosphere reserves.
• World Conservation Monitoring Center has recognized 37,000 protected areas.
• There are 448 wildlife sanctuaries and 90 national parks in India.
• In wildlife sanctuaries, protection is given only to animal life while in national parks, both flora and fauna are protected.
• The concept of biosphere reserves was launched under the MAB program of UNESCO (started in 1975).Total biosphere reserves in India are 14.
• A biosphere reserve is made of core, buffer, and transition zones. In core or natural zone, no human activity is allowed.
• Research and educational activities are allowed in buffer zone.
• Activities such as settlements, cropping, grazing, forestry, and tourism are allowed in transition zone.

Scared Grooves

• Sacred forests (islands of pristine forests): Examples are forests of Jaintia and Khasi (Meghalaya), Aravalli (Rajasthan), Western Ghats (Maharashtra and Karnataka), Surguja, Chanda, and Bastar area (MP).
• Sacred lakes: Examples are Pushkar lake in Rajasthan and Khecheopalri lake in Sikkim.
• Sacred plants: Examples are Ocimum sanctum (tulsi), Elaeocarpus floribundus, and Ficus religiosa.

Ex situ Conservation Strategies

• These include botanical gardens, zoological parks and wildlife safari parks, arboreta, aquaria, seed bank, DNA banks, tissue culture, horticultural trade, etc.
• Cryopreservation (at temperature 196°C) is useful for conserving vegetatively propagated crops, e.g., potato. There are two types of cryopreservation:
  • Very rapid cooling (e.g., storing seeds)
  • Gradual cooling and simultaneous dehydration (e.g., tissue culture)
• More than 1500 botanical gardens and arboreta and 800 professionally managed zoos are present around the world.

Biodiversity Hotspots

• The concept was developed by Norman Myers in 1988. Spots with accelerated habitat loss are priority areas for in situ conservation. These areas show high species richness and high endemism.
• India with 2.4% land area accounts approximately 8% species of the world.
• Initially 25 terrestrial hotspots were identified glob- ally. But now the number is raised to 34 with an area of less than 2%.
• Among 34, three (Western Ghats and Sri Lanka, Indo Burma, and Himalayas) are found in India. Eastern Himalayas are active center of evolution of many angiosperms and have many primitive angiosperms.
• The protection of these areas can reduce mass extinction by almost 30%.
• IUCN and WWF (World Wide Fund for Nature) are leading international organizations concerned with biodiversity conservation.

Some Abbreviations

• NEERI: National Environment Engineering Research Institute
• UNEP: United Nations Environment Program
• CAZRI: Central Arid Zone Research Institute (Jodhpur)
• BRP: Biosphere Reserve Program
• MAB: Man and Biosphere
• IBWL: Indian Board of Wild Life
• CITES: Convention on International Trade in Endangered Species
• CBD: Convention on Biological Diversity (The Earth Summit, 1992)

 

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: Western Ghats are included among the hot spots of biodiversity.

Reason: Western Ghats have greater amphibian diversity than Eastern Ghats.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 2. Assertion: Tropical regions are more diversity-rich in comparison to temperate areas.

Reason: Availability of more solar energy directly affects the presence of more species in these areas.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 3. Assertion: The process of extinction is random.

Reason: Any species not adapted to environmental conditions cannot survive.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 4. Assertion: Habitat destruction is the main reason of loss of biodiversity.

Reason: This actually causes the increase in edge area and reduction in core area.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 5. Assertion: Pristine forests are among in situ conservation strategies.

Reason: These are sacred grooves where biota is protected on site.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Ecosystem Introduction

According to Tansley (who also coined the term ecosystem), the sum total of interaction between living (biotic) and non-living (abiotic) components which is capable of independent existence is called an ecosystem.

Some other terms used for ecosystem are biocoenosis (by C. Mobius), microcosm (by Forbes), and geobiocoenosis (by Sukhachev).

Important Facts About Ecosystem

• The flow of energy is from producer to consumers.
• Cycling of matter takes place between biotic and abiotic components.
• There exists functional relationship between organisms and the environment.
• There is a great deal of biotic diversity.
• Homeostasis (self-regulation): The ecosystem has the capacity to overcome forces which tend to disturb the balance of the ecosystem (resilience).
• Incomplete ecosystem: An ecosystem lacking one or more structural components is called an incomplete ecosystem, e.g., deep sea and freshly formed rain water pond ecosystem.
• Artificial ecosystems: These are man-made ecosystems. Examples are modern agriculture, dams, zoo-logical parks, plantations, aquacultures, etc.
• The characteristics of artificial ecosystems are as follows:
  • Artificial ecosystems do not possess self-regulatory mechanism.
  • These have little diversity.
  • The food chain is simple.
  • Productivity is high.
  • There is little cycling of nutrients.

Structure And Function Of Ecosystem

Structure of Ecosystem

The structure of ecosystem depends upon the following components:

• Species diversity components of ecosystem
• Species composition
• Life cycle
• Stratification

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Function of Ecosystem

The edaphic functional components of ecosystem are studied with the following aspects:

• Productivity
• Mineral cycling
• Energy flow
• Food chain and web slopes
• Efficiency
• Biotic interrelationships
• Homeostasis
• Ecoregulation

Homeostasis in Ecosystem

Ecosystem maintains functional balance or homeostasis among different components. It is due to the following reasons:

• Carrying capacity
• Nutrient cycling
• Self-regulation
• Feedback

Stratification

Stratification is the structure or recognizable pattern in the spatial arrangement of the members of communities. More specifically, stratification represents vertical zonation in the community. For example, in grassland communities, there is subterranean floor containing basal portions of vegetation. However, stratification in a forest community is the most complicated where as many as five vertical subdivisions may be recognized. These vertical subdivisions are as follows:

• Subterranean
• Forest floor
• Herbaceous vegetation
• Shrubs
• Trees

Boundaries of Ecosystems

An ecosystem is generally regarded as a self-sufficient unit and a separate entity. However, it never operates in isolation. Boundaries between one ecosystem and another are indistinct and overlapping and all ecosystems on the earth are joined together to form a single global ecosystem known as biosphere, Some exchange of materials and energy always occurs between different ecosystems through geological, climatic, or biological processes.

Productivity Of Ecosystem

• Coral reefs, tropical rain forests, and sugarcane are most productive.
• Deserts and deep sea ecosystems are least productive.

Energy

An ecosystem is maintained by the flow of energy derived from the sun. Energy trapped by plants varies from ecosystem to ecosystem energy absorption at different levels.

• Gross primary productivity (GPP): It is the rate of organic matter synthesized by producers per unit area per unit time.
• Net primary productivity (NPP): It is the rate of organic matter built up or stored by producers in their bodies per unit time and area. Net productivity is equal to gross primary productivity minus loss due to respi- ration and other reasons.
  NPP = GPP- Respiratory loss
  The annual NPP of the whole biosphere is approximately 170 billion ton (dry wt.) of organic matter. Despite occupying about 70% of the surface, the productivity of oceans is only 55 billion ton.
• Secondary productivity: The rate of increase in energy containing organic matter or biomass by heterotrophs or consumers per unit time and area is known as secondary productivity.
• Community productivity: It is the rate of net synthesis of built-up of organic matter by a community per unit time and area.
• Ecological efficiency/trophic level efficiency: The percentage of energy converted into biomass by a higher trophic level over the energy of food resources available at the lower trophic level is called ecological efficiency.
• Photosynthetic efficiency = Gross primary productivity/Incident total solar radiation
• Net production efficiency = Net primary productivity/Gross primary productivity x 100

Decomposition

Decomposition is the process of physical and chemical breakdown of complex organic remains by organisms called decomposers, so as to produce inorganic raw materials (CO2, H2O, minerals, etc.) for recycling. The major site for decomposition is the upper layer of soil in terrestrial habitats and the bottom of water bodies. Freshly deposited organic matter constitutes raw material and is called litter. Detritus is degrading dead organic matter.

It is differentiated into above-ground and below-ground detritus. Above-ground detritus consists of dried plant parts (leaves, twigs, bark, and flowers), excreta, and dead remains of animals. Below-ground detritus is also called root detritus because it is mainly composed of dead roots. Underground organisms and their excreta also form a pan of below-ground detritus.

Decomposition Processes

Three types of processes occur simultaneously during the decomposition of detritus, viz. fragmentation, leaching, and catabolism.

• Fragmentation of detritus: Small invertebrate animals, called detrivores, feed on detritus, e.g., earthworms and termites. They bring about its frag- mentation. A part of detritus eaten by detrivores comes out in a highly pulverized state in their feces. Due to fragmentation during eating and pulverization in digestive tracts, detritus is changed into fine particles which have a large surface area.
• Leaching: Parts of soluble substances present in the fragmented and decomposing detritus (e.g., sugars and inorganic nutrients) get leached to the upper layers of soil by percolating water.
• Catabolism: It is carried out by saprotrophic bacteria and fungi. They secrete digestive enzymes over the fragmented detritus. The enzymes change complex organic compounds into simple compounds. Inorganic substances are also released in the process.

The rate of catabolic action or breakdown of different complex substances is different. This differential decomposition produces two substances: humus and inorganic nutrients in processes, respectively, called humification and mineralization, which occurs in soil.

• Humification: It is the process of particle decomposition of detritus to form humus. Humus is a dark-colored amorphous partially decomposed organic matter rich in cellulose, lignin, tannins, resin, etc., because of its highly resistant nature. It is slightly acidic, colloidal, and functions as a reservoir of nutrients.
• Mineralization: It is the release of inorganic substances (e.g., CO2, H2O, and minerals) from organic matter during the process of decomposition. These are formed along with simple and soluble organic substances when digestive enzymes are poured over organic matter by saprotrophic microbes.

Factors Affecting Decomposition

The rate of decomposition of detritus is controlled by a number of factors.

• Chemical nature of detritus: The decomposition of detritus is slow if it contains lignin, chitin, tannins (phenolics), and cellulose. It is rapid if detritus possesses more of nitrogenous compounds (such as proteins and nucleic acids) and reserves carbohydrates.
• Soil pH: Detrivores are fewer in acidic soils. Microbial activity is also low in such soils. Therefore, the rate of decomposition of organic matter is slow in acidic soils. Partially decomposed organic matter piles up over such soils. Detrivores are abundant in neutral and slightly alkaline soils while decomposer microbes are rich in neutral and slightly acidic soils.
• Temperature: At a temperature of more than 25°C, decomposers are very active in soils having good moisture and aeration. In humid tropical regions, it does not take more than 3-4 months for complete decomposition of detritus. However, under low temperature conditions (> 100°C) of soils, the rate of decomposition is very slow even if moisture and aeration are optimum.
• Moisture: Optimum moisture helps in quicker decomposition of detritus. Reduction in moisture reduces the rate of decomposition in areas of prolonged dryness such as tropical deserts where otherwise the temperature is quite high. Excessive moisture also impedes decomposition.
• Aeration: It is required for the activity of decomposers and detrivores. A reduced aeration will slow down the process of decomposition.

Energy Flow

• Food chain: It is a sequence of living organisms in which one organism consumes another due to interdependence.
• Key industry animals: These are herbivores who convert plant matter into animal matter.
  There are three types of industry animals:
  • Grazing food chain (GFC)/predator food chain major in aquatic ecosystems
  • Detritus food chain-major in terrestrial ecosystems
  • Parasitic food chain
• DFC
  • Source of energy is detritus not sun.
  • It is composed of a long chain of detritus-eating organisms (detritivores).
  • In some ecosystems (e.g., tropical rain forests), more energy flows in this chain than in the GFC.
• Food web: The interconnected food chains operating in an ecosystem are called food webs. It is, thus, a collection of food chains.
• Standing state or standing quality: It is the amount of inorganic substances present in an ecosystem per unit area at a given time.
• Standing crop: It is the amount of living material present in different trophic levels at a given time. It is commonly expressed as the number of organisms per unit area.

Ecological Pyramids

Ecological pyramids (Eltonian pyramids) were developed by Charles Elion in 1927. They are graphical representation of dif- ferent ecological parameters. In the pyramid, producers form the base and top carnivores the tip. The pyramid can be upright, inverted, or spindle shaped. These are of three types:

• Pyramid of number: Upright for grassland and pond and inverted for parasitic ecosystem.
• Pyramid of biomass: Upright for terrestrial habitats and inverted for aquatic habitats.
• Pyramid of energy: Always upright.

Ecological Succession (By Hult)

Every community undergoes a series of changes until a group of organisms is established which can live and reproduce most successfully in the area. This is called biotic succession. A biotic community normally undergoes continuous changes. The interactions among organisms in a community collectively constitute biotic factors; these influence the structure, composition, and function of a community.

Generally, a definite and orderly sequence of communities gradually appears in an area over a period of time. The first community which appears on an area is called pioneer community. A specific sequence of development of a community is related to a particular set of physical and chemical conditions. This is known as a sere, and is composed of a number of biotic communities replacing each other in the course of time called seral communities. The last community is called climax or a climatic climax (as it mostly depends upon climate).

• Primary succession: It occurs on biologically sterile area which has no record of any previous vegetation. The conditions are extreme and it takes very long time (1000 years) to complete, i.e., establishing climax community, e.g., newly created pond.
• Secondary succession: It occurs on an area that was previously occupied by vegetation and was later destroyed by fire, deforestation, over-grazing, volcanic eruptions, and floods. Humus is already present and environment is not so hostile. Therefore, it takes lesser time.
• Autogenic and allogenic succession: When a community replaces the other due to the modification of the environment by the community itself, the succession is called autogenic. On the contrary, when a community replaces the other largely due to the forces other than the effects of communities on the environment, the succession is said to be allogenic.
• Autotrophic and heterotrophic succession: Autotrophic succession is characterized by early dominance of autotrophic organisms and begins in predominantly inorganic environment. On the contrary, heterotrophic succession is characterized by early dominance of heterotrophs and begins in a predominantly organic environment.

Process of Succession

Major steps in a primary autotrophic succession are as follows:

• Nudation: An area is exposed.
• Migration: The process of dispersal of seeds, spores, and other structures of propagation of the species to bare area is known as migration.
• Germination: It occurs when conditions are favorable.
• Ecesis: Successful germination of propagules and their establishment in a bare area is known as ecesis.
• Colonization and aggregation: After ecesis, the individuals of the species increase in number as a result of reproduction.
• Competition and co-action: Due to limited resources, species show both inter and intraspecific competition. This results in the elimination of unsuitable and weaker plants.
• Invasion: Various other types of plants try to establish in the spaces left by the elimination of plants due to competition.
• Reaction: The newly arrived plants interrupt with the existing ones. As a result of reaction, the environment is modified and becomes unsuitable for the existing community which sooner or later is replaced by another community.
• Stabilization: It is the process when the final climax community becomes more or less stabilized for a longer period of time and can maintain itself in equilibrium with the climate of the area. As compared to the seral stage community, the climax community has larger size of individuals, complex organization, complex food chains and food webs, more efficient energy use, and more nutrient conservation.

Major Trends During Succession

• There is an increase in structural complexity.
• Diversity of species tends to increase.
• Biomass and standing crop increase.
• There is a decrease in net community production. There is an increase in non-living matter.
• Food chain relationship becomes complex.
• Niche becomes specific and narrower.
• Energy use and nutrient conservation efficiency increase.
• Stability increases.

Contents of Ecological Succession

• Lithosere (succession on desert/rock):
  • Lichen stage: Wind borne lichen propagules settle on the wet rock surface soon after rain or heavy dew. They develop attaching structure rhizenes. The pioneer lichens are usually crustose lichens, e.g., Graphis, Rhizocarpon, etc. They secrete lichen acids and carbonic acid. The acids slowly corrode rock surface and release minerals required for the proper growth of larger lichens, i.e., foliose lichens, e.g., Parmelia.
  • Moss stage: Foliose lichens growing on rocks make the conditions favorable for the growth of hardy mosses. Ultimately, the spot becomes suitable for invasion by the next stage (e.g., Hypnum and Bryum).
  • Annual grass stage: The mat formed by mosses on the partially fragmented rock becomes sufficiently moist during the rainy season for the germination of seeds of annual grasses and other hardy herbs, e.g., Aristida, Poa, and Eleusine.
  • Perennial grass stage: Annual grasses are replaced by perennial grasses due to increased moisture and soil in the rock crevices. The perennial grasses have runners and rhizomes which rapidly spread the grasses, e.g., Cymbopogon and Heteropogon.
  • Shrub stage: Seeds and rhizomes of xerophytic shrubs invade the area occupied by perennial grasses, e.g., Zizyphus, Capparis, Rhus, and Rubus. Shrubs are larger and their roots reach greater depth causing further cracks in the rocky substratum and, hence, helping in more soil formation.
  • Climax community: Several hardy and light demanding trees grow in the area occupied by shrubs. Slowly the environment becomes more moist and shadier so that plants. of climax community spread in the area. The type of climax community depends upon the climate. Therefore, it is also called climatic climax community.
• Hydrosere (succession on pond):
  • Plankton stage: It is the pioneer stage of hydrosere. Planktons reach the water body through wind or animals. The first to appear are minute autotrophic organisms called phytoplankton, e.g., diatoms; green flagellates; single-celled, colonial, or filamentous green algae; as well as blue green algae. They multiply rapidly. Soon a balance is created by the appearance of zooplankton which feeds on ohytoplankton.
  • Submerged stage: The bottom lined by soft mud having organic matter is favorable for the growth of submerged plants such as Hydrilla, Potamogeton, and Najas.
  • Floating stage: Floating leaved anchored plants (e.g., Nymphaea, Nelumbo, and Nuphar) appear where water becomes shallow. These plants have subterranean stems like rhizome and tuber. The plants make the water rich in mineral and organic matter. It becomes suitable for the growth of free floating plants such as Lemna, Spirodela, Wolffia, Azolla, and Eichhornia.
  • Reed swamp stage: Amphibious plants grow when the water body becomes shallow (0.3-1 m). Examples are Phragmites, Typha, Scirpus, and Sagittaria. The plants of swamp stage transpire nice quantities of water.
  • Sedge or marsh meadow stage: The shores built up in reed swamp stage are invaded by Carex (sedge); Cyperus; Juncus; grasses such as Themeda; and herbs such as Campanula, Caltha, and Polygonum. The plants transpire rapidly and add abundant humus.
  • Scrub/woodland stage: The periphery of sedge meadow stage is invaded by some rhizome bear- ing shrubby plants which can tolerate bright sunlight as well as water logged conditions, e.g., Cornus (bogwood), Cephalanthus (button brush); etc. They invite invasion by trees capable of bearing bright sunlight and water logging, e.g., Populus (cottonwood) and Alnus (alder).
  • Climax forest: New trees invade the area. They have shade-loving seed plants. These trees grow to greater heights.

Nutrient Cycling

Nutrient cycling is of three types:

• Gaseous: Examples are carbon (absorbed as CO2), nitrogen, oxygen (as vapors), and main reservoir pool (as atmosphere or water).
• Sedimentary: Biogenetic materials are nongaseous and have lithosphere as the main reservoir pool. Examples are P, Ca, and Mg. Both sedimentary and gaseous phases occur in case of sulfur.
• Mixed: Nutrients have both gaseous and nongaseous states, e.g., sulfur. Tundra consists of plains with snow, ice, and frozen soil (permafrost).

Aquatic Biomes

Five general categories of aquatic ecosystems are usually recognized:

• Marine pelagic areas within the water mass of oceans with water of high salinity
• Marine benthic areas on the ocean floor with water of high salinity
• Estuaries, bodies, or oceanic water near the mouths of freshwater rivers with intermediate salinity
• Freshwater lotic with flowing water of low salinity Freshwater lentic with non-flowing water of low salinity

Marine Biome

The marine environment is characterized by its high concentration of salt (about 3.5% in open sea) and mineral ions (mostly sodium and chloride followed by sulfur, magnesium, and calcium). All ocean basins are roughly of the shape of a wash basin (or an inverted hat).

From the coastline, a gradually sloping region extends to about 160 km into the sea. This zone, with a depth of 8-200 m, is called the continental shelf. The angle of the slope then abruptly steepens to form the continental slope which levels off into a more or less horizontal expanse forming the ocean floor.

The vertical zones of the ocean are determined on the basis of availability of light for photosynthesis.

• The well-lit upper 200 m forms the photic or euphotic zone.
• The next zone up to the depth 200-2000 m gets less light which is insufficient for photosynthesis and forms disphotic zone.
• Below 2000 m is the area of perpetual darkness-the abyssal zone/dark zone.

Freshwater Biomes (Lakes and Ponds)

Freshwater biomes are stationary water bodies. Ponds are small and shallow. Lakes are larger and deeper. Lakes develop in na- ture due to the following reasons:

• Glaciation
• Natural or man-made depressions
• Oxbow lakes which develop from the main stream of a river

Depending upon productivity, lakes are of three types:

• Oligotrophic lakes: These lakes are deep with rocky steep sides and with less circulation of nutrients. They have little biota but are rich in green algae. Brackish lakes are oligotrophic and also occur in arid areas, e.g., Sambhar Lake in Rajasthan.
• Eutrophic lakes: These lakes are rich in biota and have quick circulation of nutrients. These are shallow with abundant blue green algae, e.g., Dal Lake in Kashmir.
• Dystrophic lakes: These lakes are rich in humic acid and are less productive.

Life Forms

Raunkiaer (1934) has distinguished plants into five forms on the basis of size, shape, branching, crown, life span, and perennation.

• Phanerophytes: Perennial herbs, shrubs and trees, epiphytes, succulents, lianas, etc., where perennating buds occur at a height of 10 cm or more above the ground level.
• Chemaephytes: Small plants of cold areas where perennating buds or shoot apices lie at or above the ground level.
• Hemieryptophytes: Perennating structures occur at the ground level. Aerial shoots die with the onset of winter, e.g., rosette plants.
• Cryptophytes: Perennial plants with underground storage parts. These are of different types such as
  • Geophytes: These Subterranean perennating structure (root, root tuber, bulb, stem tuber, rhizome, corm).
  • Halophytes (marshy plants): Perennating structure embedded in mud.
  • Hydrophytes (aquatic plants)
  • Thorophytes: Plants which perennate in the form of seeds.

Ecosystem Services

The products of ecosystem processes are called ecosystern services, e.g., healthy forest ecosystems purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, provide wildlife habitat, maintain biodiversity, pollinate crops, provide storage site for carbon, and also provide aesthetic, cultural, and spiritual values.

Researchers like Robert Constanza et. al. have put an average price tag of US$ 33 trillion a year on these fundamental ecological services (i.e., nearly twice the value of a global GNP – US$ 18 trillion).

Out of total cost, soil formation accounts for about 50%, recreation and nutrient cycling less than 10% each, and climate regulation and habitat for wildlife account for about 6% each.

 

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: Agriculture and aquacultures are man-maintained ecosystems.

Reason: All biotic and abiotic factors are managed by humans in these ecosystems.

Answer. 1. In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

Question 2. Assertion: Warm and moist environment can enhance the rate of decomposition.

Reason: Warm and moist climate leads to create anaerobic condition which promotes decomposition.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 3. Assertion: Detritus food chain begins with decomposers.

Reason: Detrivores, like fungi and bacteria, are major decomposers in such food chains.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 4. Assertion: Ecological pyramids cannot explain all vital functions of any ecosystem.

Reason: Pyramids actually do not explain the role of organisms working at more than one trophic level.

Answer. 2. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 5. Assertion: Successional process starts only in those areas where no living organisms ever existed.

Reason: These areas are not supported by physical environmental conditions.

Answer. 4. If both Assertion and Reason are false, then mark (4)

Organisms And Populations

Habitat: A specific place (or locality) where an organism usually lives. It is a physical entity comprising the sum total of the abiotic factors to which a species or a group of species is exposed.

Ecological niche (J. Grinnel): It represents the functional role and status of a species in the environment. It represents habitat and trophic level of a species. No two species can have the same niche even if they are found in the same environment

Population: A group of individuals of the same species in a well-defined geographical area which share or compete for similar resources and can potentially interbreed. Their study links ecology to genetics and evolution of a population.

Community: A number of interrelated populations of different species sharing a common environment.

Ecosystem: A functional unit of nature in which living organisms interact with one another and with their surrounding physical environment.

Biosphere: Any part of atmosphere inhabited by organisms.

Ecology deals with the various principles which govern the relationships between organisms and their environment. The term “ecology” was first used by Reiter in 1868. Ernst Haeckel (1886) first correctly defined ecology as the science dealing with reciprocal relationship of organisms and the external world. Warming (1895) employed this science for the study of plants. E.P. Odum (1963) defined it as the “study of structure and function of nature.”

Clarke, Warming, Weaver, Clements, Schimper, Dauben-malre, Raunkiaer, E.P. Odum, and H.T. Odum are some renowned ecologists. Prof. R. Misra is known as the “Father of Ecology in India.” Other famous Indian ecologists include G.S. Puri and S.C. Pandeya. Ecology gives a holistic perspective to biology.

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Branches Of Ecology

• Autecology: Ecology of individuals or species, essentially physiological ecology.
• Synecology: Study of relationships between communities and environment.
• Genecology: Study of ecological adaptations in relation to genetic variability.
• Paleoecology: Study of relationship between organisms and environment in the past.
• Applied ecology: Application of ecological concepts for human welfare.
• Systems ecology: Interpretation of ecological concepts in terms of mathematical principles.

Organisms And Their Environment

Environment is the sum total of all external factors, substances, and conditions which influence organisms without becoming their constituent part. Environment is usually divided into two parts: physical environment and biotic environment.

Factors such as components, conditions, and forces of environment which have a direct and indirect effect on the form, functioning, behavior, survival, and reproduction of organisms are called environmental factors. These are of two types: abiotic and biotic. Abiotic factors are divisible into three categories: atmospheric, edaphic, and topographic. Atmospheric factors are light, temperature, water, and wind. Edaphic factors are related to soil. Topographic factors are abiotic or physical factors related to slope, altitude, etc., connected with the surface behavior of the earth. Biotic factors are influences produced by living organisms.

Biome (Major Ecosystems)

A biome is a large natural ecosystem which is distinct in its climatic conditions and has its specific group of climax plants and associated animals. Rainfall, temperature range, nature of soil, barriers, latitude, and altitude determine the nature and extent. of biomes.

The major biomes of India are as follows:

• Tropical rain forests: In India, tropical rain forests are found mainly along Western Ghats and in north-eastern Himalayas. Dipterocarpus and hopea are the most common tree species in Indian rain forests. They show a 30-40 m tall canopy with four-five strata. Woody climbers and epiphytes grow profusely in these forests. The soil of such forests is highly leached and has a low base content. They require a mean annual temperature of 23-27 °C and 2000-3500 mm rainfall.
• Tropical deciduous forests: They occur in the northern and southern parts of our country in plains and low hilly areas. Sal, teak, and tendu are the common trees of these forests. These forests show a short structure of 10-20 m. During rainy season, the forest is lush green with dense foliage, whereas in summer, the forest is largely leafless. The soil of these forests is rich in nutrients due to less leaching. They require a mean annual temperature of 22-32°C and mean annual rainfall of 900-1600 mm.
• Desert: In these biomes, vegetation is very sparse due to extreme temperatures and very little rainfall (below 10 cm). Hot deserts are characterized by high rate of evapotranspiration and albedo. In cold deserts, the conditions are physiologically xeric and they exhibit permafrost, while in hot deserts, the conditions are physically xeric. Important trees of Indian desert are Prosopis cineraria, Acacia sp., Salvadora sp., and Tamarix sp. The common succulents are species of Euphorbia and many members of family Cactaceae.

• Coastal biome: Coastal areas are zones of transition between oceanic and terrestrial habitats and, so, are very sensitive. These are detritus-based biomes, where plants have to adapt to salinity and water-logged conditions. Mangroves are the major types along salt marshes or swamps. Mangroves are characterized by the presence of pneumatophores and viviparous seed germination. Common examples are Rhizophora, Sonneratia, Avicennia, and Laguncularia. Besides, Phoenix, Pandanus, and Casuarina are also found commonly in coastal areas.

Major Abiotic Factors

Temperature

Ecologically, it is the most relevant factor as temperature variation affects the enzyme kinetics, basal metabolic activities, and physiological functions of organisms. So, thermal tolerance de- cides to a large extent the geographical distribution of different species.

Stenothermal

Such organisms live in areas where the temperature is uniform throughout the year. These organisms cannot tolerate temperature variation.

Eurythermal

Such organisms can tolerate large changes in temperature. These organisms are classified into four temperature groups on the basis of their occurrence in different climatic zones.

• Megatherms: High temperature throughout the year as found in tropical zone.
• Mesotherms: They are adapted to winters and high summer temperature. These organisms live in subtropical zone.
• Microtherms: They live in temperate areas where the winter temperature is low but the summer temperature is moderate.
• Hekistotherms: These organisms are adapted to a brief period of summer below 10°C and a long snowy winter period. This condition occurs in arctic or alpine zone.

Some effects of temperature are defined as under:

• Bergman’s rule: Warm-blooded animals (birds and mammals) have a larger body size in cold climate than in hotter areas..
• Allen’s rule: Extremities (legs, ears, tail, and mouth) of warm-blooded animals become smaller in colder areas as compared to the animals of warmer areas.
• Renton’s rule: In a colder climate, birds possess narrow and acuminate wings as compared to broader wings of birds found in warmer areas.
• Jordan’s rule: As the temperature is lowered, some fishes possess a larger size with a larger number of vertebrae.

Thermoperiodicity

Thermoperiodicity or thermoperiodism is the response of living organisms to regular changes of temperature. It is of two types: diurnal and seasonal.

• Diurnal thermoperiodicity: It is the response of organisms to daily changes of temperature. Generally, the day-time temperature is higher while the night-time temperature is lower.
• Seasonal thermoperiodicity: It is the response of organisms to seasonal changes in temperature. Along with photoperiodicity, it controls the growth of plants.

Thermal Stratification in Lakes

The occurrence of different temperatures in different horizontal layers as in a forest or a deep water body is called thermal stratification. A deep-water body, such as a lake, has three temperature strata: epilimnion, metalimnion, and hypolimnion.

• Eplimnion: It is the upper stratum in the water body. Epilimnion is warmer during summer and cooler during winter.
• Metalimnion: It is a short transitional zone between epilimnion and hypolimnion. The middle part of metalimnion is called thermocline. It is the area of maximum temperature changes.
• Hypolimnion: It is the lower stratum of a water body with lesser temperature fluctuations.

Water

Water is an important component of protoplasm, which is a general solvent. Water is also present over more than 71% surface of the earth as oceans, lakes, rivers, ice caps, and glaciers. The seawater has a high percentage of salt content (3.5%). Water present on land is called fresh water. Its salt content is low-less than 0.5%. The salt concentration (measured as salinity in parts per thousand) is less than 5% in inland water, 30-35% in the sea, and more than 100% in some hypersaline lagoons.

The regular movement of water among various regions and components of biosphere, viz., aquatic systems, air, and land, constitutes a water cycle. Water comes over land and water bodies as precipitation or rainfall. The total global rainfall is 4.46 G. Precipitation comes from water vapors present in air. At any time, the atmosphere contains only 0.13 G of water vapors (1 G or geogram

Animals found in coastal water are called neritic and those found in open water are termed as pelagic. Pelagic organisms are plankton (if microscopic), neuston (if macroscopic and found on the surface), and nekton (if actively swimming). Organisms found at the bottom of water bodies are called benthos.

Light

Light has a wide range of spectrum. The electromagnetic spectrum is a complete range of oscillating waves that travel together through space at a speed of 3 x 105 km/s. At 83 km above the surface of the earth, solar radiation carries an energy equivalent to 2 cal/cm2/min. This value is called solar constant.

Shortwave radiations are cosmic rays (with a wavelength less than 10-5 nm), gamma rays (103-105 nm), X-rays (10-1–10-2 nm), and UV rays (100-400 nm).

All shortwave radiations are extremely harmful. Most of them are trapped in ionosphere and mesosphere. UV rays are also harmful.

UV-C and half of UV-B radiations are absorbed by the ozone layer of the stratosphere. A large amount of the rest is dissipated by the particles of troposphere; only a small amount reaches the earth.

Light affects photosynthesis, growth, reproduction, movement, stratification, photoperiodism, and phenology in plants, whereas it affects migration, reproduction, development, pigmentation, locomotion, and the period of activity in animals.

Light Zonation of Lakes

• Littoral zone: It is exposed to wave action and is highly productive.

• Limnetic zone: It is an open water body.
• Euphotic zone: This zone receives maximum light above the light compensation point.
• Disphotic zone: This zone receives diffused light at or below the light compensation point. It is also known as the twilight zone.
• Profundal (dark, abyssal) zone: It has no light.
• Benthic zone: It lies at the bottom of the sea.

Soil

Soil Composition

Soil consists of four components: two solid and two nonsolid. The solid components are mineral particles and organic matter. The nonsolid components are air and water. A fifth component of variable nature is soil organisms.

Chief characteristics of soil are studied with the help of a soil profile. The type of soil profile depends upon the climate and vegetation of the area. The smallest three-dimensional volume of the soil required to study the profile is called pedon. Most soils possess three-four horizons and a number of subhorizons. A soil horizon is a horizontal layer approximately parallel to the soil surface that possesses distinctive properties which are unlike the ones present in adjoining regions. In general, a profile consists of O, A, B, C, and R horizons.

• Weathering: It is the breaking of rocks into fine particles as present on the soil. Weathering occurs by the following methods:
  • Physical weathering: It is caused by alternate heating and cooling, alternate wetting and drying, and action of frost, snow, rain, and wind.
  • Chemical weathering: Oxidation, reduction, carbonation, and solubilization are performed to break the rock.
  • Biological weathering: It is caused by lichens, mosses, and other organisms.
• Humification: It is addition of organic matter or humus to a weathered rock. Humification is essential to starting biological activity and nutritional cycling. Humus is a dark-colored amorphous substance. It is slightly acidic and colloidal and is a reservoir of nutrients. The main functions of humus are biogeochemical cycling, preventing soil from compaction, helping in the formation of soil crumbs, and improving the aeration and water-holding capacity of the soil. It also makes the soil spongy, therefore, rendering it easy for penetration by roots.
• Eluviation and illuviation: The two processes bring about transport and deposition of materials in the soil. Eluviation is washing down of materials from the upper strata of soil and helping in enriching the different layers of soil with minerals. Illuviation is deposition of minerals in the lower strata of soil.
• Mineral matter: It consists of inorganic substances present as particles of different sizes and composition.
  • Gravel: It is made of fine pebbles with a size of 2-10 mm.
  • Sand: It consists of grains of quartz or silicon dioxide (SiO2). Size varies from 0.02-2.0 mm. Sand is chemically inert. It allows quick percolation of rain or irrigation water. Aeration is good.
  • Silt: It is formed of fine grains of quartz. The size is 0.002-0.02 mm. It is chemically inert.
  • Clay: It is made of Al, Fe, and Si. The size is less than 0.002 mm. Clay particles are chemically active and have fine interspaces that can hold abundant water, but aeration is poor.
  • Soil air: It is the air present in macropores with a size between 20 and 50 μm. A good soil should have 25% air by volume. Soil air is required for the respiration of roots and several microorganisms. Soil air is richer in CO2 and poorer in O2.
  • Soil porosity: It is the percentage of interspaces present per unit dry weight of soil. The value of soil porosity is 30% in sandy soil, 45% in loam soil, and 50% in clay soil. There are two types of soil pores: micropores and macropores. Micropores are small sized interspaces having a diameter of 20 μm or less. These hold water by capillarity. Macropores are interspaces with a size of more than 20 μm.
    Residual soils develop in situ. Transported soils are brought from other places through gravity (colluvial), running water (deposited on flood plains and called alluvial), wind (colian or acolian), and glacier (glacial soil).

Soil Types

• Red soils: These are acidic laterite soils which are deficient in lime, magnesium, phosphorus, and potassium but rich in organic matter, iron, and aluminum. These soils support tea, coffee, rubber, cardamom, areca nut, and paddy plantation.
• Black soils: Also called black cotton soils, locally known as regular, these soils have dark brown or black color from organic matter, clay/hydrated iron, aluminum silicate, and undifferentiated B-horizon (A-C soil).
• Terai/Bhabar soils: These soils are mostly colluvial and highly productive.

Soil Texture

There are three main types of soil textures.

• Sandy soils: These soils contain about 80% or more of sand, the remaining being silt and clay. Sandy soils are porous and loose. Their water-holding capacity is poor and there is little chemical nutrition.
• Clay soils: These are soils having 40-50% clay, the rest being silt. Sand is little. Clay soils have abundant capillary pores; therefore, their water-holding capacity is high. Inorganic nutrients are available in good quantity. However, aeration is poor.
• Loam soils: These soils contain 20% clay, 40% sand, and 40% silt. These have good mineral nutrition, aeration, and hydration. Therefore, loam soils are the best for plant growth.

Soil pH

Soil pH determines the type of soil microorganisms, solubility of different minerals, and the type of plants which will grow on it. In alkaline soils (pH above 7), there is reduced availability of Zn, Mn, Cu, and Fe. In acidic soils, there is an abundance of Fe, Mn, and Al but deficiency of Ca, Mg, and K. Certain soils possess excess of salts, especially of Na and Mg. These are called saline soils. Salinity increases with excessive irrigation. Another category of infertile soil is alkali soil.

Topography

Topography, i.e., surface configuration of an area (physical features like hills, plains, or slopes), also influences the distribution of organisms. For example, the center and edge of a pond or a stream, the top side and underside of a rock, and the north and south face of a ridge or a mountain are usually inhabited by different species of organisms,

Response To Abiotic Factors

A change in one environmental factor leads to change in others also. In other words, all factors are integrated. An organism would have evolved various mechanisms to maintain its internal environment at homeostasis to perform its physiological and biochemical functions. This constancy is necessary for its overall fitness or maximum performance. This may be maintained naturally or artificially.

• Regulate: All birds and mammals and a few lower vertebrates and invertebrates maintain homeostasis by physiological or behavioral means such as thermoregulation and osmoregulation. But plants do not have such mechanisms to regulate homeostasis. The evolutionary success of mammals is believed largely due to this ability.
• Conform: When organisms cannot maintain thermal and osmotic balance with their environment, they adopt this mechanism, e.g., approximately 99% plants and animals. Thermoregulation is energetically expensive, especially for small animals having large surface area relative to their volume. Due to this, very small animals are rare in polar regions. Some species have the ability to regulate up to a limited range beyond which they become conform (partial regulators).
  For localized or short outburst of stressful conditions, organisms show migration or suspended growth.
• Migrate: It is the temporary movement of organisms from a stressful area to a more favorable one in terms of food, shelter, spawning, or climate. For example, Siberian cranes migrate from Siberia to Keoladeo National Park, also known as Bharatpur Bird Sanctuary, in Rajasthan. Locums migrate for food and salmon fish migrates for spawning. Similarly, ungulate’s migration in Africa takes place for food.
• Suspend: It is a stage in the life cycle of organisms where they change their developmental/physiological structural/biochemical behavior to pass through unfavorable conditions. Examples are thick-walled spores in bacteria, fungi, and lower plants; dormancy in seeds and other vegetative parts in higher plants; and hibernation (winter sleep) among organisms which are un- able to migrate, e.g., bears.
• Aestivation: It is the metabolic inactivity of organisms during hot desiccating summer, e.g., snails and fish.
• Diapause: It is the stage of temporary suspension of development under unfavorable conditions, e.g., zoo- plankton in lakes and ponds.

Adaptation

Adaptation is an attribute of an organism that enables it to survive and reproduce in its habitat. Adaptations may be morphological, physiological, or behavioral. These are either fixed genetically or remain epigenetic.

Some examples of adaptation are as follows:

• The kangaroo rat of North American desert fulfills its water demands by internal oxidation of fats. It also has the ability to concentrate its urine.
• Mammals from a colder climate generally have shorter ears and limbs to minimize heat loss. Here, Allen’s rule is at work.
• Seals have a thick layer of fat (blubber) below the skin to reduce loss of body heat.
• Altitude sickness can be expressed at high altitudes where body does not get enough oxygen due to low atmospheric pressure, causing nausea, fatigue, and heart palpitations. Under these conditions, the body increases RBC production, decreases the binding capacity of fibrils, and increases breathing rate. These physiological adaptations allow organisms to respond quickly to stressful conditions.
• Archaebacteria can flourish at a temperature exceeding 100°C, while humans can perform metabolism in a narrow range (37°C).
• Antarctic fishes can survive below 0°C, and a variety of invertebrates and fishes are adapted biochemically to survive great depths with crushing pressure.
• Desert lizards lack the physiological ability to cope with extreme temperatures, but manage the body temperature by behavioral means.

Water-Based Adaptations

On the basis of dependence of plants on water and their relationship with water, Warming (1909) recognized three kinds of plant communities: hydrophytes, xerophytes, and mesophytes.

Hydrophytes: They live in abundance of water with at least their lower parts (roots) and leaves submerged.

Roots of hydrophytes are poorly developed/completely absent in Wolffia, Ceratophyllum, etc.

• Stems in hydrophytes are of three kinds:Reduced in free floating plants (e.g., Pistia).
• Narrow and slender in submerged, suspended plants (e.g., Hydrilla and Ceratophyllum).
• Well-developed in amphibious plants and rhizome growing through the mud (e.g., Nymphaea and Typha).

Leaves in hydrophytes are of the following kinds:

• Usually long ribbon-like (e.g., Potamogeton) or finely divided (e.g., Ranunculus).
• In some hydrophytes, leaves of different forms are produced by the same plant-aerial leaves are not dissected but submerged ones are dissected (e.g., Ra-nunculus aquatilis and Limnophila. This is known as heterophylly.
• Petioles become long, swollen, and spongy (e.g., Nymphaea, Nelumbo, and Saggitaria).

Hydrophytes show the following anatomical adaptations:

• There is no cuticle over the epidermis.
• Stomata either are absent or are dysfunctional.
• Aerenchyma is well developed.
• Epidermal cells contain chloroplasts.
• Mechanical tissues such as sclerenchyma and collenchyma are poorly developed.
• Vascular tissues are poorly developed,
• Secondary growth is absent.
• Vegetative propagation is common by runners (e.g., Marsilea), offsets (e.g., Pistia and Eichhornia), rhizomes (e.g., Typha), and turions (fleshy buds, e.g., Potamogeton).
• Xerophytes: These plants show anatomical and physiological adaptations.Anatomical adaptations: Thick-walled epidermal cells, multiple epidermis (e.g., Nerium), thick cuticle, hypodermis sclerenchymatous, stomata sunken and covered by hair (e.g., Nerium, Casuarina, and Ephedra), water storing parenchyma well developed, conducting and mechanical tissues well developed, palisade multilayered, and cells of succulents contain abundant mucilage.
• Physiological adaptations: Reduction of transpiration, high osmotic potential, and resistance to desiccation of mucilage to hold water.

On the basis of the nature of soil and causes of unavailability of water, xerophytes are divided into the following categories:

• Physical xerophytes: These plants grow in soils. which are physically dry (due to shortage of water), e.g., Opuntia, Casuarina, Ruscus, Muehlenbeckia (Coccoloba), etc.
• Physiological xerophytes: These plants grow in soils having sufficient water which is not available due to high salt concentration (salinity) or very low temperature.

On the basis of life cycle and water storage, xerophytes are divided into the following categories:

• Ephemerals: These plants are short-living, i.e., have a brief lifespan (6-8 weeks). These evade dry season by disappearing, leaving behind their seeds. Hence, these plants are not true xerophytes, rather drought evaders and drought escapers, e.g., Cassia tora and Tribulus.
• Succulents (fleshy xerophytes): These plants absorb a large quantity of water during rainy season and store it in different body parts. These suffer only externally. Hence, these are drought avoiding or drought-resistant xerophytes. These are further divided into the following:
  • Stem succulents: e.g., Opuntia, Euphorbia antiquorum, E. splendens, E. tirucolli, and Cereus.
  • Leaf succulents: e.g., Aloe, Agave, Begonia, and Bryopnyiium.
  • Root succulents: e.g., Asparagus and Hebe parviflora.
• Nonsucculents: These plants are drought endurers and true xerophytes, and can withstand long drought periods (perennial nonsucculents), e.g., Casuartna, Zizyphus, Nenrium, Calotropis, Acacia, and Capparis.

Halophytes: Halophytes are special types of xerophytic plants which grow in saline soils with high concentrations of salts such as NaCl, MgCl2, and MgSO (hence, physiologically dry soil). Halophytic communities growing on swamps are called halophytes.

Population

Population is of two types. One is called deme, which stands for local population living in a specific area. The other is meta population, which consists of the whole set of local populations connected by dispersing individuals.

For the purpose of ecological studies, a group of individuals resulting from asexual reproduction is also considered population.

Population Attributes/Group Attributes

Some characteristics are unique to the group and are not the characteristics of the individuals forming it; for example, an organism is born and dies, and has a specific age, but it does not have birth rate, death rate, and age ratio.

Population characteristics can be best expressed by statistical methods. Some important characteristics are discussed next.

Population Density

Density is the number of individuals per unit area; e.g., millions of Spirogyra filaments in a pond or 200 Parthenium plants in an area. This can also be expressed as “the population biomass per unit area or volume” when we have to count a large number of organisms or find out the role of a single huge banyan tree in an area.

Relative density is a good measure of finding out the total density of fishes in a lake by counting the number of fishes caught per trap. Another example of measuring the size of a population is tiger census in India. This census is based on pug marks and fecal pellets which are used to indirectly estimate the population size of tigers.

Age Ratio Pyramids

An age pyramid is a graphic representation of the proportion of various age groups in a population. There are three types of age pyramids: triangular, bell-shaped, and urn-shaped.

Triangular pyramid: It is the graphic representation of a young or growing population and has a very high proportion of pre-reproductive individuals.

Bell-shaped pyramid: The pyramid is bell-like with pre-reproductive individuals only marginally more than the reproductive individuals. The population is mature or stable.

Urn-shaped pyramid: It has a small number of pre-reproductive individuals, a larger number of reproductive individuals, and a small number of post- reproductive individuals. Such a population shows negative growth.

Population Growth

Some attributes of population are used to estimate its growth as population size may fluctuate in a given habitat in a given period due to changes in the four basic processes discussed as under.

• Natality: It is the birth rate (an inherent ability of a population to increase) and refers to the number of births in the population during a given period that are added to its initial density.
  The per individual change in a population due to natal- ity can be estimated using AN/Nat,
  where AN, is the number of new individuals produced, Nis the initial population, and At is the change in time.
• Mortality: It is the death rate (the number of individual dying in a population in a given period).
• Immigration: It is one-way permanent inward movement of individuals of the same species into a habitat with existing population. This may help to speed up the growth or prevent extinction of a smaller population. In plants, it is a settlement of disseminules.
• Emigration: It is one-way permanent outward movement of a number of individuals from a population to other habitat area, hence, reducing the size of that local population. Plants are fixed and, so, do not show emigration.

By these population characteristics, the density of a population (M) at time t can be expressed after a period of time t+1 as

N(+1) = N; + [(B + 1) − (D + E)]

where B is the number of births, I is the number of immigrants, D is the number of deaths, and E is the number of emigrants.

So, it can be concluded that births and deaths are the most important factors influencing population density.

Growth Models

Biotic potential and environmental resistance: Biotic potential (r) is the maximum or potential natality. The sum of environmen- tal factors that limits the population size is called environmental resistance. Environmental resistance rises with the rise in popula- tion size. The influence of environmental resistance over biotic potential is denoted by (K – N)/N.

Carrying capacity (K): The maximum number of individuals of a population which can be supported with optimum resources for their survival is called the carrying capacity of the environment. The growth of a population depends on its biotic potential, death rate, and birth rate. Depending upon the amplitude of these three, a population may show exponential growth and logistic growth.

• Exponential growth: Darwin believed a population grows geometrically when the resources are unlimited, as each species realizes its inherent potential to grow. This intrinsic rate of natural increase is called r. The value of r is an important parameter to assess the impact of environmental factors on population growth.
  • Any increase or decrease in a population N during time t (dNidt) will be dN/dt = (b-d) x N, where b is the per capita birth rate and d is the per capita death rate. If (bd) = r, then, dN/dt = rN.
  • The magnitude of r was 0.0205 for human population in India, while it reached 0.0176 in 2001. For Norway rat, it is 0.015 and for flour beetles, it is 0.12.
  • Equation dN/dt = rN describes geometric growth resulting in a J-shaped curve. Such population stops abruptly due to environmental resistance, which suddenly becomes effective, or depletion of a resource. Decline in a J-shaped population is density-triggered, e.g, algal blooms insect population.

• Logistic growth: This growth form is characterized by a function of carrying capacity (K) for a given population, giving it a more realistic form. Such forms are represented under limited resource conditions, where a population finally reaches an asymptote. This growth form can be described as the Verhulst-Pearl logistic growth and is expressed as
  dN/dt = rN(K-N/K)
  • Life history variation: Any variation in life history is evolved in relation to the selection pressure imposed by environmental factors in order to achieve the most efficient reproductive strategy such as the following:
    • A small number of large-sized individuals are produced (e.g., mammals and birds).
    • A larger number of small-sized individuals are produced (e.g., oysters and fishes).
    • Some organisms breed once in their life time (e.g., Bambusa and Pacific salmon).
    • Some organisms breed many times during their life-time (e.g., mammals and many birds).

Population Interactions

Many populations of different species may require a similar set of environmental gradient where they live and interact with each other and environment in order to survive and perform their activities. These interactions may be assigned “+,” “_” or “0,” where “+” is beneficial, “-” is detrimental, and “0” is neutral.

• Negative interactions: These are interactions between two species where one species affects others’ growth and survival.
• Competition: It is a process in which the fitness (r) of one species is significantly lower in the presence of other species.
  • Competition affects plants and herbivores more than carnivores.
  • This may occur between totally unrelated species when they compete for the same resource, e.g., competition for zooplankton between visiting flamingoes and resident fishes in South American lakes.
  • Resources need not be limiting for competition to occur; the feeding efficiency of one species might be reduced due to the inhibitory or interfering presence of other species.

According to Gause’s competitive exclusion principle, two closely related species competing for the same resources cannot coexist indefinitely and the competitively inferior species will be eventually eliminated. Gause performed his experiments on two species of Paramecium: P. aurelia and P. caudatum.

Coexistence: Species facing competition might evolve a mechanism to live in the same niche by changing the feeding time or foraging patterns. This is called resource partitioning. For example, five closely related species of warblers avoid competition by changing their foraging pattern..

Habitat diversification can also reduce competition, e.g., Tribolium and Oryzaephilus. Tribolium Trifolium model best explains both exclusion and coexistence. There are some circumstantial evidences which support the exclusion of species due to competition. For example,

• Introduction of goats resulted in the exclusion of Abingdon tortoise from Galapagos Islands.
• The same interaction occurs between Balanus and Chthamalus on the rocky coasts of Scotland.

Competitive release: There occurs a dramatic increase in the population of a less distributed species in a geographical area when its superior competitor is removed experimentally from that area.

Predation: It is an interaction between species involving killing and consumption of prey.

Predation plays the following roles:

• Transfer of energy (in ecological sense, herbivores are not very different from predators).
• Keeping prey population under control.
• The rabbit population in Australia increased tremendously because the land does not have its natural predators. The introduction of prickly pear cactus (Opuntia) in Australia was controlled only after the introduction of its natural predator moth (Cactoblastis cactorum). Similarly, red foxes in New Zealand have become top carnivores due to the absence of a natural carnivore.
• Predators help maintain species diversity in a community as they can reduce the intensity of competition among prey species; e.g., experimental removal of Pisaster (star fish) resulted in the extinction of more than ten species of invertebrates.
• According to the Slobodkin’s principle of prudent predator, a predator does not exterminate its prey by overexploitation.

For their defense, prey species have evolved various adaptations, which are listed as follows:

• Monarch butterfly is well known for its general unpalatability to its predator birds. This insect is able to sequester highly toxic glycosides present in milkweeds on which its caterpillar stages feed. There larvae develop on milkweed providing the protection to plant against herbivory.
• Cardiac glycosides are produced by Calotropis. Nicotine, caffeine, quinine, and strychnine are other means of chemical defense in plants.
• The association of bullhorn Acacia cornigera with Pseudomyrmex ferruginea (acacia ant) is a defense against herbivory. This is also an example of coevolution.

Parasitism: This also depresses the growth rate of a population or may reduce the total size of the population. Parasites are generally smaller. Majority of them are host-specific. A high reproductive potential, loss of digestive system and unnecessary sense organs, and the presence of specific sucking or adhesive organs are some of their characteristics, but they have poor means of dispersal.

Various types of parasites are given as follows:

• Ectoparasites: Examples are lice on humans, ticks on dogs, copepods on marine fishes, and Cascuta on hedge plants.
• Endoparasites: These are extremely specialized parasites, with a complex life cycle but simplified morphologically and anatomically. Examples are liver fluke, plasmodium, etc.
• Brood parasitism: An example of this type of parasitism is cuckoo which lays its eggs in a crow’s nest.
• Hyperparasites: Examples are bacteriophages, which are parasite over parasitic bacteria. Similarly, Pasteurella pestis is a parasite of rat flea, which is a rat parasite.
• Amensalism (-, 0): It is both a detrimental and a neutral relationship, where chemical secretion by one organism inhibits the growth of the other. Examples are allelopathic plants such as Prosopis juliflora and black walnut.

Positive interactions: It is an association between two species where one or both populations realize positive effects. This is necessary to achieve homeostasis.

Commensalism (+, 0): It is the simplest form of interaction, in which one species is benefitted while the other is neither harmed nor benefitted. Examples are orchid epiphytes on mango trees, cattle egret and grazing cattle, barnacles growing on the back of a whale, clown fish and sea anemone, and pilot and sucker fish with shark.

Mutualism (+, +): It is an obligatory relation where both species are benefitted. It is essential for their survival on the earth. Examples are mutualistic N2-fixing relation, lichens, mycorrhiza, termite-intestinal flagellate relation, and plant-pollinator relation. Sometimes, it is a one-to-one coevolution- ary relation such as fig and wasp relation, Ophrys and Colpa relation, and Yucca and Pronuba relation.

Some insects such as queens of Bombus affinis cheat plants to steal nectar from the spurs of Aquilegia.

Proto-cooperation (+, +): It is a nonobligatory relation where organisms of both species are benefitted. Examples are oxpecker and rhinoceros, and plover bird and crocodile.

 

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: Holistic approach explains the environmental interactions.

Reason: All environmental factors are integrated with no limits of time and space.

Answer. 3. If Assertion is true but Reason is false, then mark (3)

Question 2. Assertion: Some organisms can maintain internal homeostasis by means of physiological processes and are called “regulates.”

Reason: Regulates can maintain internal homeostasis only up to a limit under stressful conditions.

Answer. 3. If Assertion is true but Reason is false, then mark (3)

Question 3. Assertion: Population ecology is a link of ecology to population genetics and evolution.

Reason: Natural selection operates at population level to evolve the desired traits.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 4. Assertion: Under unlimited resource conditions, a population can show an exponential growth curve.

Reason: The maximum possible number of individuals can always be supported when enough resources are available.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark

Question 5. Assertion: Insects contribute the maximum to the total diversity of animals.

Reason: Angiosperms and insects are coevolved to perform as plant-pollinator.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

BioTechnology And Its Applications

Biotechnological Applications In Agriculture

• Food production can be enhanced by
  • Agro-chemical based agriculture,
  • Organic agriculture, and
  • Genetically engineered crop-based agriculture.
• The Green Revolution resulted in increasing the food supply almost three times.
• It refers to the great increase in the production of food grains (especially wheat and rice) that resulted in large part from the introduction of new, high yielding varieties beginning in the mid 20th century.
• Its early dramatic successes were in Mexico and the Indian subcontinent.
• The new varieties required large amount of chemical fertilizers and pesticides to produce high yields, raising concern about cost and potentially harmful environmental effects.
• This demands an alternate pathway that can result in maximum yield from the fields but the use of chemicals and fertilizers is minimum, i.e., harmful effects on the environment are reduced.
• Genetically modified organisms or GMO can be the plants, bacteria, fungi, and animals whose genes have been altered by genetic manipulation.

Genetically Modified Crops

• A transgenic crop is a crop that contains and expresses a transgene.
• A popular term for transgenic crops is genetically modified crops or GM crops.
• The techniques used for the production of transgenic crops offer the following two unique advantages: (a) any gene (from any organism or a gene synthesized chemically) can be used for transfer and (b) the change in genotype can be precisely controlled since only transgene is added into the crop genome.
• In contrast, breeding activities can use only those genes which are present in the species that can be hybridized within them.
• In addition, changes occur in all those traits for which the parents used in hybridization differ from each other.
• When a transgene is introduced into the genome of an organism, it achieves one of the following:
  • Produces a protein (that is the product in which we are interested)
  • Produces a protein (that on its own produces the desired phenotype)
  • Modifies an existing biosynthetic pathway (so that a new end-product is obtained)
  • Prevents the expression of an existing native gene
• Hirudin is a protein that prevents blood clotting. The gene encoding hirudin was chemically synthesized. This gene was then transferred into Brassica napus, where hirudin accumulates in seeds. Hirudin is purified and used as medicine. In this case, the transgene product itself is the product of interest.

Read and Learn More NEET Biology Notes

• The tomato variety “Flavr Savr” presents an example where the expression of a native tomato gene has been blocked.
• The expression of a native gene can be stopped by many different methods.
• Fruit softening is promoted by the enzyme polygalacturonase which degrades pectin.
• The production of polygalacturonase was blocked in the transgenic tomato variety Flavr Savr.
• Therefore, the fruits of this tomato variety remain fresh and retain their flavor much longer than do the fruits of normal tomato varieties. In addition, the fruits have a superior taste and increased total soluble solids-these are unexpected bonus.

Genetically Modified Food

• Food prepared from the produce of genetically modified (transgenic) crops is called genetically modified food or, in short, GM food. GM food differs from the food prepared from the produce of conventionally developed varieties mainly in the following aspects.
  • Firstly, GM food contains the protein produced by the transgene in question, e.g., cry protein in case of insect-resistant varieties.
  • Secondly, it contains the enzyme produced by the antibiotic resistance gene that was used during gene transfer by genetic engineering.
  • Finally, it contains the antibiotic resistance gene itself.
• It has been argued that the above features of GM foods can lead to the following problems when they are consumed.
  • Firstly, the transgene product may cause toxicity and/or produce allergies.
  • Secondly, the enzyme produced by the antibiotic resistance gene can cause allergies, since it is a foreign protein.
  • Finally, the bacteria present in the alimentary canal of humans can take up the antibiotic resistance gene that is present in the GM food.
  • These bacteria would then become resistant to the concerned antibiotic.
  • As a result, these bacteria can become difficult to manage.
• Scientists involved in the production of transgenic crops are addressing these concerns.
  • Efforts are being made to use other genes in place of antibiotic resistance genes.
  • The toxic and allergenic actions of the transgene product can be adequately examined by detailed assays using suitable animal models.

Biological Transcription

GM Products: Benefits And Controversies

Benefits

Crops

• Enhanced taste and quality.
• Reduced maturation time.
• Increased nutrients, yields, and stress tolerance.
• Improved resistance to disease, pests, and herbicides.
• New products and growing techniques.

Animals

• Increased resistance, productivity, hardiness, and feed efficiency.
• Better yields of meat, eggs, and milk.
• Improved animal health and diagnostic methods.

Environment

• “Friendly” bioherbicides and bioinsecticides.
• Conservation of soil, water, and energy.
• Bioprocessing for forestry products.
• Better natural waste management.
• More efficient processing.

Society

• Increased food security for growing populations.

Controversies in Terms of Safety

• Potential human health impact: Allergens, transfer of antibiotic resistance markers, and unknown effects.
• Potential environmental impact: Unintended transfer of transgenes through cross-pollination, unknown effects on other organisms (e.g., soil microbes), and loss of flora and fauna biodiversity.

Bt Cotton

• DNA technology makes it possible to locate the genes that produce Bt proteins lethal to insects and transfer the genes into crop plants.
• First, scientists identify a strain of Bt that kills the targeted insect.
• Then they isolate the gene that produces the lethal protein.
• This gene is removed from the Bt bacterium and a gene conferring resistance to a chemical (usually antibiotic or herbicide) is attached (which proves useful in later steps).
• The Bt gene with the resistance gene attached is inserted in plant cells.
• These modified or genetically transformed cells are then grown into a complete plant by tissue culture.
• The modified plant produces the same lethal protein as produced by the Bt bacteria because plants now have the same gene.
• B. thuringiensis form protein crystals during a particular phase of their growth.
• These crystals contain a toxic insecticidal protein.
• Why does this toxin not kill the Bacillus? Actually, the Bt toxin protein exists as inactive protoxin; but once an insect ingests the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilizes the crystals.
• The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause cell swelling and lysis and, eventually, cause the death of the insect.
• Bt is not harmful to humans, other mammals, birds, fish, or beneficial insects.
• Specific Bt toxin genes were isolated from B. thuringiensis and incorporated into several crop plants such as cotton.
• The choice of genes depends upon the crop and the targeted pest, as most Bt toxins are insect-group specific.
• The toxin is coded by a gene named cry. There are a number of them. For example, the proteins encoded by genes cry I Ac and cry II Ab control the cotton bollworm and that by cry I Ab control corn borer.

• Although Bt genes have been introduced into tobacco, tomatoes, cotton, and other broadleaf plants, gene transfer technology for corn is a recent achievement.
• The development of corn plants expressing Bt proteins requires substantial changes in the Bt genes, including the creation of synthetic versions of the genes, rather than the microbial Bt gene itself.

Pest – Resistant Plants

• Root-knot nematode is the most economically important group of plant-parasitic nematodes worldwide. It attacks nearly every food and fiber crop grown (about 2000 plant species in all).
• Nematodes invade plant roots. By feeding on the roots’ cells, they cause the roots to grow large and form galls, or knots, damaging the crop and reducing its yield.
• The most cost-effective and sustainable management tactic for preventing root-knot nematode damage and reducing growers’ losses is to develop resistant plants that prevent the nematode from feeding on the roots. Because root-knot nematode resistance does not come naturally in most crops, bioengineering is required. Four common root-knot nematode species (mainly Meloidegyne incognitia) account for 95% of all infestations in agricultural land.
• By discovering a root-knot nematode parasitism gene that is essential for the nematode to infect crops, scientists have developed a resistance gene effective against all four species.
• Using a technique called RNA interference (RNAi), researchers have effectively turned nematode’s biology against itself.
• They genetically modified Arabidopsis, a model plant, to produce double-stranded RNA (dsRNA) to knock out the specific parasitism gene in the nematode when it feeds on the plant roots.
• RNAi takes place in all eukaryotic organisms as a method of cellular defense.
• This method involves the silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents the translation of the mRNA (silencing).
• The source of this complementary RNA could be an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate.
• Using Agrobacterium vectors, nematode-specific genes were introduced into the host plant.
• The introduction of DNA was such that it produced both sense and anti-sense RNA in the host cells.

• These two RNAS being complementary to each other formed a dsRNA that initiated RNAi and, thus, silenced the specific mRNA of the nematode.
• The consequence was that the parasite could not survive in a transgenic host expressing siRNA.
• The transgenic plant, therefore, got itself protected from the parasite.
• This knocked out the parasitism gene in the nematode and disrupted its ability to infect plants. (No natural root-knot resistance gene has this effective range of root-knot nematode resistance.)
• Efforts have been directed primarily at understanding the molecular tools the nematode uses to infect plants.
• This is a prerequisite for bioengineering durable resistance to these nematodes in crop plants.

Biological Transcription

Biotechnological Application In Medicine

Therapeutic Agents

• Proteins with potential as pharmaceutical agents are produced by using genetically engineered organisms.
• Enzymes have also been used for this purpose, e.g., DNase I and alginate lyase have been used in aerosols. Some known examples are as follows:
  • Human growth hormone obtained from E. coli is used for the treatment of dwarfness.
  • Chorionic gonadotropin hormone produced by genetic engineering is used for the treatment of infertility.
  • Interferons produced by E. coli are commercially used for the treatment of viral infections and cancer. These were first obtained through DNA recombinant technique by Charles Weisman in 1980. He inserted the gene for interferon production in E. coli.
  • Interleukins produced by E. coli are used for stimulating immunity system.
  • Tissue plasminogen activator (tPA)-an enzyme is used for dissolving blood clot after heart attack and stroke.
  • Antihemophilic human factor VIII is used by people with hemophilia to prevent and control bleeding or to prepare them for surgery.
  • Platelet-derived growth factor produced by recombinant DNA technology is useful for stimulating wound healing.
  • Penicillin G acylase is also produced by genetic engineering. This enzyme is used for converting penicillin into 6-aminopenicillin acid for the formation of new antibiotics.

Genetically Engineered Insulin

• Since the discovery of insulin by Banting and Best (in 1921) and its use for the treatment of diabetes, it was derived from the pancreatic glands of abattoir animals.
• This hormone, produced and secreted by the beta cells of the pancreas islets of Langerhans, regulates the use and storage of food, particularly carbohydrates.
• Although bovine and porcine insulin are similar to human insulin, their composition is slightly different. It, therefore, causes adverse effects due to regular injection, being a foreign substance.
• This observation led to the synthesis of human insulin which is chemically identical to its naturally-produced counterpart.
• Insulin consists of 51 amino acids forming two short polypeptide chains: chain A with 21 amino acids and chain B with 30 amino acids.
• The two chains are linked by disulfide bond. In animals, including humans, insulin occurs as proinsulin.
• It is made of chain A, chain B, and chain C (30 amino acids). As the insulin matures, chain C is removed.
• The genetic engineering of insulin begins with the identification and separation of DNA sequences coding for chain A and chain B.
• This was found to be present at the top of the short arm of the 11th chromosome.
• It contains 153 nucleotides-63 nucleotides for chain A and 90 nucleotides for chain B.
• These sequences were introduced into the plasmid (pBR322) of E. coli-common human colon bacterium.
• It is said to be the factory used in the genetic engineering of insulin.
• In E. coli, B-galactosidase controls the transcription of these genes. Therefore, the insulin gene needs to be tied to this enzyme.
• The protein formed by E. coli consists partly of B-galactosidase joined to either A or B chain of insulin.
• These are then extracted from ẞ-galactosidase fragment and purified.
• The two chains are mixed and reconnected in a reaction that forms disulfide bridges resulting in pure humulin–the synthetic human insulin.

Gene Therapy

• Much attention has been focused on the so-called genetic metabolic diseases in which a defective gene causes an enzyme to be either absent or ineffective in catalyzing a particular metabolic reaction effectively.
• A potential approach to the treatment of genetic disorders in man is gene therapy.
• This is a technique in which the absent or faulty gene is replaced by a working gene, so that the body can make the correct enzyme or protein and, consequently, eliminate the root cause of the disease.
• The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency.
• This enzyme is crucial for the immune system to function.
• The disorder is caused due to the deletion of the gene for adenosine deaminase.
• In some children, ADA deficiency can be cured by bone marrow transplantation; in others, it can be treated by enzyme replacement therapy, in which functional ADA is given to the patient by injection.
• But the problem with both these approaches is that they are not completely curative.
• As a first step towards gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body.
• A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are subsequently returned to the patient.
• However, as these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes.
• However, if the gene isolated from marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.
• Before the treatment of a genetic disease begins, an accurate diagnosis of the genetic defect needs to be made.
• It is here that biotechnology is also likely to have a great impact in the near future.
• Genetic engineering research has produced a powerful tool for pinpointing specific diseases rapidly and accurately.
• Short pieces of DNA called DNA probes can be de- signed to stick very specifically to certain other pieces of DNA.
• The technique relies upon the fact that complementary pieces of DNA stick together.
• DNA probes are more specific and have the potential to be more sensitive than conventional diagnostic methods. It should be possible in the near future to distinguish between defective genes and their normal counterparts. (This is an important development.)

Biological Transcription

Molecular Diagnosis

• For the effective treatment of a disease, early diagnosis and understanding its pathophysiology are very important.
• Using the conventional methods of diagnosis (serum and urine analysis, etc.), early detection is not possible.
• Recombinant DNA technology, polymerase chain reaction (PCR), and enzyme linked immuno-sorbent assay (ELISA) are some of the techniques that serve the purpose of early diagnosis.
• The presence of a pathogen (bacteria, virus, etc.) is normally suspected only when the pathogen has produced a disease symptom.
• By this time, the concentration of pathogen is already very high in the body.
• However, very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by the amplification of its nucleic acid by PCR, which is now routinely used to detect HIV in suspected AIDS patients.
• It is being used to detect mutations in genes in suspected cancer patients too.
• It is a powerful technique to identify many other genetic disorders.
• DNA is usually isolated from white blood cells and has to be cut into smaller pieces to be analyzed.
• This is accomplished by restriction enzymes. Eco RI (a restriction enzyme from E. coli) will cut DNA wherever the sequence “GAA TTC” appears.
• An exposure to this enzyme results in the DNA being chopped into millions of fragments (called restriction fragments) of varying size.
• Once cut, the DNA is loaded into a well on one end of a slab of gel.
• The fragments are then separated according to size by electrophoresis.
• As electric current passes through the gel, the fragments move according to size.
• Bigger fragments stay close to the origin and smaller fragments move farther down the length of the gel.
• The DNA is then denatured (by exposure to alkaline solutions) to render the DNA single stranded (instead of the natural double-stranded form).
• Since the gel is difficult to handle, the DNA is transferred to a nitro cellulose paper to create a Southern blot (named after the researcher who developed the procedure).
• The DNA probe which is radioactively labeled (or fluorescently labeled) is then applied to the Southern blot.
• Since the probe is also single-stranded, it will seek the single-stranded DNA fragments that are complementary, and undergo hybridization.
• The excess probe is washed out and only the bound probe will remain on the Southern blot paper.
• This is then laid on an X-ray film.
• The radioactive probe will leave bands on the X-ray film.
• Depending on the type of probe used, there can be hundreds of bands (much like barcodes) or only a few bands present on the X-ray film.
• By having several wells on the end of the gel, several samples can be loaded and DNA fragments in the corresponding lanes can be analyzed concurrently.
• By running control samples, with known DNA fragment sizes, on the same gel with patient samples, it is possible to identify changes in the size of a DNA fragment and, therefore, the change in a specific gene.
• Since each step takes about a day and since samples are batched, the procedure ordinarily takes one to two weeks to complete.
• ELISA is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected either by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesized against the pathogen.

Transgenic Animal

• There are various definitions for the term “transgenic animal.”
• A transgenic animal is one whose genome has been changed to carry genes from other species.
• The nucleus of all cells in every living organism contains genes made up of DNA.
• These genes store information that regulates how our bodies form and function.
• Genes can be altered artificially, so that some characteristics of an animal are changed.
• For example, an embryo can have an extra, functioning gene from another source artificially introduced into it, or it can have a gene introduced which can knock out the functioning of another particular gene in the embryo.
• Animals that have their DNA manipulated in this way are known as transgenic animals.
• The majority of transgenic animals produced so far are mice the animal that pioneered the technology.
• The first successful transgenic animal was a mouse. A few years later, it was followed by rabbits, pigs, sheep, and cattle.

How are Transgenic Animals Produced?

• To date, there are three basic methods of producing transgenic animals:
  • DNA microinjection
  • Retrovirus-mediated gene transfer
  • Embryonic stem cell-mediated gene transfer
• Gene transfer by microinjection is the predominant method used to produce transgenic farm animals.
• Since the insertion of DNA results in a random process, transgenic animals are mated to ensure that their offsprings acquire the desired transgene.
• However, the success rate of producing transgenic animals individually by these methods is very low and it may be more efficient to use cloning techniques to increase their numbers.
• For example, gene transfer studies revealed that only 0.6% of transgenic pigs were born with a desired gene after 7,000 eggs were injected with a specific transgene.

How do Transgenic Animals Contribute to Human Welfare?

• The benefits of these animals to human welfare can be grouped into the following areas:
  • Agriculture
  • Medicine
  • Industry
• The following examples are not intended to be complete but only to provide a sampling of the benefits.

Agricultural Applications

• Breeding: Farmers have always used selective breeding to produce animals that exhibit desired traits (e.g., increased milk production and high growth rate). Traditional breeding is a time consuming, difficult task. When technology using molecular biology was developed, it became possible to develop traits in animals in a shorter time and with more precision. In addition, it offers the farmer an easy way to increase yields.
• Quality: Transgenic cows exist that produce more milk or milk with less lactose or cholesterol, pigs and cattle that have more meat on them, and sheep that grow more wool. In the past, farmers used growth hormones to spur the development of animals; but this technique was problematic, especially since the residue of the hormones remained in the animal product.
• Disease resistance: Scientists are attempting to produce disease-resistant animals, such as influenza-resistant pigs, but a very limited number of genes are currently known to be responsible for resistance to dis- eases in farm animals.

Medical Applications

• Xenotransplantation: Patients die every year for the lack of a replacement heart, liver, or kidney. For example, about 5,000 organs are needed each year in the United Kingdom alone. Transgenic pigs may provide the transplant organs needed to alleviate the shortfall. Currently, xenotransplantation is hampered by a pig protein that can cause donor rejection but research is underway to remove the pig protein and replace it with a human protein.
• Nutritional supplements and pharmaceuticals: Products such as insulin, growth hormone, and blood anti-clotting factors may soon be or have already been obtained from the milk of transgenic cows, sheep, or goats. Research is also underway to manufacture milk through transgenics for the treatment of debilitating diseases such as phenylketonuria (PKU), hereditary emphysema, and cystic fibrosis.
• In 1997, the first transgenic cow, Rosie, produced hu- man protein-enriched milk (2.4 g/L). This transgenic milk is a more nutritionally balanced product than the natural bovine milk and can be given to babies or the elderly with special nutritional or digestive needs. Rosie’s milk contains the human gene a-lactalbumin.
• Vaccine safety: Transgenic mice are being developed for use in testing the safety of vaccines before the vaccines are used on humans. These mice are being used to test the safety of the polio vaccine. If successful and found to be reliable, they can replace the use of monkeys to test the safety of batches of the vaccine.

Biological Transcription

Industrial Applications

• In 2001, two scientists at Nexia Biotechnologies in Canada spliced spider genes into the cells of lactating goats.
• The goats began to manufacture silk along with their milk and secrete tiny silk strands from their body by the bucketful.
• By extracting polymer strands from the milk and weaving them into thread, scientists can create a light, tough, flexible material that can be used in applications such as military uniforms, medical microsutures, and tennis racket strings.
• Toxicity-sensitive transgenic animals have been produced for chemical safety testing.
• Microorganisms have been engineered to produce a wide variety of proteins, which in turn can produce enzymes that can speed up industrial chemical reactions. The anthrax bacterium is sent through letters after September 2001.
• Mass-produced pathogens or their toxins are delivered either as powder or in the form of spray, using a variety of delivery devices.
• Bioweapons are low-cost weapons. These cause far more casualties than chemical or conventional weapons. Bioweapon agents are invisible and extremely difficult to detect.
• These features make bioweapon agents very convenient for use by terrorists and even governments. (Both have used them on a limited scale.)
• The possible defenses against bioweapons include the use of respirator or gas mask, vaccination, administration of appropriate antibiotics, and decontamination. In addition, sensitive detection systems should be developed to control and minimize damage.

Bioethics

• Ethics include a set of standards by which a community regulates its behavior and decides as to which activity is legitimate and which is not.
• Therefore, bioethics may be viewed as a set of standards that may be used to regulate our activities in relation to the biological world.
• Biotechnology, particularly recombinant DNA tech- nology, is focused on exploiting the biological world in ways that are usually unprecedented.
• Therefore, biotechnology has been labeled variously, ranging from “unnatural” to “detrimental” to “biodiversity.”
• The major bioethical concerns pertaining to biotechnology are as follows:
  • The use of animals in biotechnology causes great suffering to them.
  • When animals are used for the production of pharmaceutical proteins, they are virtually reduced to the status of a “factory.”
  • Introduction of a transgene from one species into another species violates the “integrity of species.”
  • The transfer of human genes into animals (and vice versa) dilutes the concept of “humanness.”
  • Biotechnology is disrespectful to living beings; it only exploits them for the benefit of human be- ings.
  • Biotechnology may pose unforeseen risks to the environment, including risk to biodiversity.
• These arguments may seem quite attractive.
• It may be pointed out that biotechnology usually does only what was being done before.
• However, biotechnologies do these things on a much larger scale and at a much faster rate.
• Each society has to evaluate for itself the validity of these and other arguments related to biotechnology.
• It also has to decide the kinds of activities that it considers acceptable and those that it does not.
• Going beyond the morality of such issues, the biological significance of such things is also important.
• Genetic modification of organisms can have unpredictable results when such organisms are introduced into the ecosystem.
• Therefore, the Indian Government has set up organizations such as GEAC (Genetic Engineering Approval Committee), which will make decisions regarding the validity of GM research and the safety of introducing GM-organisms for public services.
• The modification/usage of living organisms for public services (as food and medicine sources, for example) has also created problems with patents granted for the same.

Biopatent

• A patent is a right granted by a government to an inventor to prevent others from the commercial use of his invention.
• A patent is granted for (a) an invention (including a product), b) an improvement in an earlier invention, (c) the process of generating a product, and (d) a concept or design.
• Initially, patents were granted for industrial inventions, etc.
• But at present, patents are being granted for biological entities and for products derived from them; these patents are called biopatents.
• Primarily, industrialized countries such as the USA, Japan, and the members of European Union are awarding biopatents.
• Biopatents are awarded for the following:
  • Strains of microorganisms
  • Cell lines
  • Genetically modified strains of plants and animals
  • DNA sequences
  • The proteins encoded by DNA sequences
  • Various biotechnological procedures
  • Production processes
  • Products
  • Product applications
• There has been a great deal of opposition from the various social groups to the patenting of life forms.
• The nature of these objections is mainly ethical and political.
• The arguments in favor of biopatents are primarily of increased economic growth.
• Many biotechnology patents are very broad in their coverage.
• For example, one patent covers “all transgenic plants of Brassica family.”
• Such broad patents are considered morally unacceptable and fundamentally inequitable, since these would enable financially powerful corporations to acquire monopoly control over biotechnological processes.
• They may, in the end, even come to control the direction of agricultural research, including plant breeding.
• Such a position would pose a threat to global food security.
• Many organizations and multinational companies exploit and/or patent biological resources, or bioresources, of other nations without proper authorization from the countries concerned; this is known as biopiracy.
• Industrialized nations are rich in technology and financial resources but poor in biodiversity and traditional knowledge related to the utilization of bioresources.
• In contrast, developing nations are poor in technology and financial resources, but are rich in biodiversity and traditional knowledge related to bioresources.
• Biological resources (or bioresources) include all those organisms that can be used to derive commercial benefits.
• Traditional knowledge related to bioresources is the knowledge developed by various communities over long periods of history regarding the utilization of bioresources, e.g., the use of herbs, etc., as drugs.
• Often, this traditional knowledge can be exploited to develop modern commercial processes.
• The traditional knowledge suggests the direction to be followed, and saves considerable time, effort, and expenditure for their commercialization.
• Institutions and companies of industrialized nations are collecting and exploiting the bioresources as follows:
  • They are collecting and patenting the genetic resources themselves. For example, a patent granted in the USA covers the entire basmati rice germplasm indigenous to our country.
  • The bioresources are being analyzed for the identification of valuable biomolecules. (A bio-molecule is a compound produced by a living organism.) The biomolecules are then patented and used for commercial activities.
  • Useful genes are isolated from the bioresources and patented. These genes are then used to generate commercial products.
  • The traditional knowledge related to bioresources is utilized to achieve these objectives. In some cases, the traditional knowledge itself may be the subject of patent.
• A West African plant, Pentadiplandra brazzeana, produces a protein called brazzein, which is approximately 2000 times as sweet as sugar.
• In addition, brazzein is a low-calorie sweetener.
• Local people have known and used the super-sweet berries of this plant for centuries.
• But the protein brazzein was patented in the USA.
• Subsequently, the gene encoding brazzein was also isolated, sequenced, and patented in the USA.
• It is proposed to transfer the brazzein gene into maize and express it in maize kernels.
• These kernels will then be used for the extraction of brazzein.
• This development can have serious implications for countries exporting large quantities of sugar.
• Bioresources of the developing world have always been commercially exploited by the industrialized nations without an adequate compensation to the developing world.
• This exploitation has dramatically increased in pace with the development of powerful analytical tools and techniques.
• There has been a growing realization of this injustice and demands are being made for adequate compensation and benefit sharing.
• Some nations are developing comprehensive laws to prevent unauthorized exploitation of their bioresources and traditional knowledge.
• The Indian Parliament has recently cleared the second amendment of the Indian Patents Bill, which takes such issues into consideration, including patent terms, emergency provisions, and research and development initiative.

Choose the correct answer:

Question 1. Which one of the following can be used as a permanent cure for ADA deficiency?

1. Bone marrow transplantation on detection of disorder in adults.
2. Enzyme replacement therapy at any point in life.
3. Both (1) and (2).
4. Gene therapy at early embryonic stages.

Answer. 4. Gene therapy at early embryonic stages.

Question 2. Which one of the following is a transgenic product useful for the treatment of hemophilia?

1. Factor VIII
2. Antithrombin II
3. α-1-antitrypsin
4. Lysostaphin

Answer. 1. Factor VIII

Question 3. Who is responsible for obtaining interferons through re- combinant DNA technique?

1. A.R. Bounting
2. Eli Lily
3. Charles Weissmann
4. A. Tiselius

Answer. 3. Charles Weissmann

Question 4. Select the incorrect statement:

1. RNAi silencing takes place in all eukaryotic organ- isms as a method of cellular defense.
2. RNAi requires silencing of mRNA by binding of complementary ssDNA molecule.
3. Complementary nucleic acid could be from mobile genetic elements (transposons).
4. Ti plasmid with nematode-specific genes has been used in RNAi.

Answer. 2. RNAi requires silencing of mRNA by binding of complementary ssDNA molecule.

Question 5. Which gene controls the transcription of chain A and chain B required for humulin synthesis in E. coli?

1. B-Lactamase
2. B-Galactosidase
3. Polygalacturonase
4. Chitinase

Answer. 2. B-Galactosidase

Question 6. Transgenic Brassica napus has been used for the synthesis of

1. Hirudin
2. Heparin
3. Polygalacturonase
4. Cry protein

Answer. 1. Hirudin

Question 7. Which genes encode the protein to control bollworm infection in cotton plants?

1. Cry II Ab
2. Cry I Ac
3. Both (1) and (2)
4. Amp

Answer. 3. Both (1) and (2)

Question 8. Which is incorrect with respect to GM food?

1. It contains the protein produced by the transgene in question.
2. GM food contains antibiotic resistance gene itself.
3. The enzyme produced by antibiotic resistance gene will not cause allergies.
4. The bacteria in gut of humans could take by antibiotic resistance gene.

Answer. 3. The enzyme produced by antibiotic resistance gene will not cause allergies.

Question 9. Golden rice-a transgenic variety of rice is principally richer than normal rice in

1. Cry I Ab
2. Hirudin
3. TPA
4. B-carotene

Answer. 4. B-carotene

Question 10. Southern blotting cannot be performed without

1. Restriction endonucleases
2. Agarose
3. Monoclonal antibodies
4. Both (1) and (2)

Answer. 4. Both (1) and (2)

Question 11. Plants, bacteria, fungi, and animals whose genes have been altered by manipulation are called genetically modified organisms (GMO). Which of the following statement is not applicable to GM plants?

1. Reduced reliance on chemical pesticides.
2. Prevent early exhaustion of fertility of soil.
3. Crops less tolerant to abiotic stress (cold, drought, salt, and heat).
4. Enhanced nutritional value of food.

Answer. 3. Crops less tolerant to abiotic stress (cold, drought, salt, and heat).

Question 12. In case of Bacillus thuringiensis, Bacillus itself is not killed by toxic protein crystals produced by it because

1. Bt toxin protein is not produced in Bacillus
2. Bt toxin protein is produced in very less amount in Bacillus
3. Bt toxin exists as inactive toxin
4. Bt toxin cannot cause any damage to Bacillus

Answer. 3. Bt toxin exists as inactive toxin

Question 13. Bt toxin kills the insect by

1. Blocking nerve conduction
2. Damaging the surface of trachea
3. Creating pores in the tracheal system
4. Creating pores in the mid gut

Answer. 4. Creating pores in the mid gut

Question 14. Which of the following cry gene codes for the protein which can control the corn borer effectively?

1. cry I Ac
2. cry II Ab
3. cry I Ab
4. cry II Ac

Answer. 3. cry I Ab

Question 15. RNA interference (RNAi) technique has been devised to protect plants from nematode. In this technique, the mRNA of nematode is silenced by _______ produced by the host plant.

1. dsDNA
2. ssDNA
3. dsRNA
4. Target proteins

Answer. 3. dsRNA

Question 16. Which of the following peptide chain is removed during the maturation of pro-insulin into insulin?

1. A peptide
2. B peptide
3. C peptide
4. A and C peptides

Answer. 3. C peptide

Question 17. Eli Lilly, an American company, prepared two DNA se- quences corresponding to A and B chains of human insulin and introduced them in the plasmids of E. coli to produce insulin chains. Chains A and B were produced separately, extracted, and combined by creating

1. Peptide bonds
2. Ionic bonds
3. H-bonds
4. Disulfide bonds

Answer. 4. Disulfide bonds

Question 18. The first clinical gene therapy was given in 1990 to a 4-year old girl with which of the following enzyme deficiency?

1. Adenosine deaminase
2. Tyrosine oxidase
3. Monamine oxidase
4. Glutamate dehydrogenase

Answer. 1. Adenosine deaminase

Question 19. Which of the following could be a permanent cure for the treatment of severe combined immunodeficiency (SCID)?

1. Bone marrow transplantation
2. Enzyme replacement therapy
3. Both (1) and (2)
4. Gene therapy

Answer. 4. Gene therapy

Question 20. Which of the following technique is being used to detect mutations in genes in suspected cancer patients?

1. PCR
2. ELISA
3. Blood analysis
4. PAGE

Answer. 1. PCR

Question 21. Animals that have had their DNA manipulated to possess and express an extra gene are known as

1. Foreign animals
2. Superior animals
3. Transgenic animals
4. Intergenic animals

Answer. 3. Transgenic animals

Question 22. About 95% of all existing transgenic animals are

1. Rabbits
2. Pigs
3. Cows
4. Mice

Answer. 4. Mice

Question 23. Today, transgenic models exist for many human diseases which includes

A. Cancer

B. Cystic fibrosis

C. Rheumatoid arthritis

D. Alzheimer’s disease

1. (A) and (C) only
2. (B) and (C) only
3. (A), (B), and (C) only
4. All of these

Answer. 4. All of these

Question 24. Which of the following is not a true statement with respect to Bt cotton?

1. Bt toxin is produced by a bacterium Bacillus thuringiensis.
2. It is an example of biopesticide.
3. Bt toxin gene has been cloned in plants to provide resistance to insects.
4. Bt cotton could decrease the amount of pesticide used.

Answer. 3. Bt toxin gene has been cloned in plants to provide resistance to insects.

Question 25. How many recombinant therapeutics have been approved for human use all over the world?

1. 12
2. 30
3. 20
4. 18

Answer. 2. 30

Question 26. Which of the following techniques serve the purpose of early diagnosis?

A. Recombinant DNA technology

B. PCR

C. ELISA

1. (A) only
2. (A) and (C) only
3. (A) and (B) only
4. All of these

Answer. 4. All of these

Question 27. Which of the following technique is based upon the principle of antigen-antibody interaction?

1. PCR
2. ELISA
3. Recombinant DNA technology
4. RNA interference

Answer. 2. ELISA

Question 28. Which of the following transgenic protein product has been used to treat emphysema?

1. α-l-Antitrypsin
2. α-Lactalbumin
3. Cry protein
4. C-peptide

Answer. 1. α-l-Antitrypsin

Question 29. How many varieties of rice have been estimated to be present in India?

1. 2000
2. 20,000
3. 2,00,000
4. 20,00,000

Answer. 3. 2,00,000

Question 30. The use of bioresources by multinational companies and other organizations without proper authorization from the countries and people concerned without compensatory payment is called

1. Bioethics
2. Biopiracy
3. Bioterror
4. Bioweapon

Answer. 2. Biopiracy

Question 31. Amongst the following, which characteristic is not applicable to Bt cotton?

1. Bt is the abbreviated term for botulinum toxin.
2. Such cotton is resistant to armyworms and beetles.
3. The toxin is activated in the body of the insect.
4. The toxin is coded by a gene called “cry.”

Answer. 1. Bt is the abbreviated term for botulinum toxin.

Question 32. Which biotechnology company is credited with the synthesis of genetically engineered human insulin for the first time?

1. Celera genomics
2. Cipla
3. Eli Lily
4. Ranbaxy

Answer. 3. Eli Lily

Question 33. Functional ADA cDNA can be introduced into the cells of the patient receiving gene therapy by using a vector constituted by

1. E. coli
2. Reovirus
3. Retrovirus
4. Agrobacterium

Answer. 3. Retrovirus

Question 34. Which variety of rice was patented by a US company even though the highest number of varieties of this rice is found in India?

1. Shamati Sonara
2. Co-667
3. Basmati
4. Lerma Roja

Answer. 3. Basmati

Question 35. Which step has the Government of India taken to cater to the requirement of patent terms and other emergency provisions in this regard?

1. Biopiracy Act
2. Indian Patents Bill
3. RTI Act
4. Negotiable Instruments Act

Answer. 2. Indian Patents Bill

Question 36. What is another term used for GMO (genetically modified organisms)?

1. Cybrid organisms
2. Genomorphic organisms
3. Transgenic organisms
4. Conjoint twins

Answer. 3. Transgenic organisms

Question 37. Transgenic models can be used to investigate several human diseases such as

1. Alzheimer’s disease
2. Cystic fibrosis
3. Carcinoma
4. All of these

Answer. 4. All of these

Question 38. Which GMO is now being developed in order to be used in testing the safety of polio vaccines before they are used in humans?

1. Transgenic sheep
2. Transgenic cow
3. Transgenic mice
4. Transgenic viruses

Answer. 3. Transgenic mice

Question 39. Which method of cellular defense is common in all eukaryotic organisms?

1. RNA interference
2. Reverse transcription
3. VNTR
4. Phagocytosis

Answer. 1. RNA interference

Question 40. “Silencing” of mRNA molecule in order to control the production of a harmful protein has been used in the protection of plants from

1. Nematodes
2. Beetles
3. Mosquitoes
4. Flies

Answer. 1. Nematodes

Question 41. Mark the odd one with respect to the advantages of genetically modified plants:

1. Production of food with better nutritional value.
2. Decrease in post harvest losses.
3. Decreased dependence on fertilizers.
4. Decreased usage of minerals.

Answer. 4. Decreased usage of minerals.

Question 42. In which disease has the advancement of genetic engineering still not been used as clinical cure?

1. Emphysema
2. Cystic fibrosis
3. Phenylketonuria
4. Anencephaly

Answer. 4. Anencephaly

Question 43. Which substance is tested in case of toxicity/safety testing using transgenic animals?

1. Chemicals
2. Pathogen
3. The amount of DNA in the cell
4. The amount of tolerable radiation levels of an organism

Answer. 1. Chemicals

Question 44. Which step proved to be the main challenging obstacle in the production of human insulin by genetic engineering?

1. Removal of C-peptide from active insulin.
2. Getting insulin assembled into a mature form.
3. Addition of C-peptide to pro-insulin.
4. Splitting A and B polypeptide chains.

Answer. 2. Getting insulin assembled into a mature form.

Question 45. What is the disadvantage of using processed insulin (from pig pancreas) in diabetic patients?

1. It leads to hypercalcaemia.
2. It may cause allergic reactions.
3. It is expensive.
4. It can lead to mutations in human recipients.

Answer. 2. It may cause allergic reactions.

Question 46. Why are repeated transfusions of genetically engineered cells required in SCID patients?

1. The transfused cells have limited lifespan.
2. The introduced gene is mutated.
3. The enzyme required is degraded after 20 days of transfusion.
4. Both (2) and (3).

Answer. 1. The transfused cells have limited lifespan.

Question 47. Which Indian plants have either been patented or attempts have been made to patent them by the Western nations for their commercial use?

1. Basmati rice
2. Turmeric
3. Neem
4. All of these have been targeted

Answer. 4. All of these have been targeted

Question 48. Why is insulin usually not administered orally to a diabetic patient?

1. Insulin is bitter in taste.
2. Insulin is a peptide.
3. Insulin will lead to a sudden decrease in blood sugar if given orally.
4. Insulin leads to peptic ulcer orally.

Answer. 2. Insulin is a peptide.

Question 49. Which technique would you expect to be completely curative in SCID?

1. Gene therapy in adult stage.
2. Gene therapy in embryonic stage.
3. Bone marrow transplantation.
4. Enzyme replacement therapy.

Answer. 2. Gene therapy in embryonic stage.

Question 50. A doctor while operating on an HIV+ patient accidentally cut himself with a scalpel. He comes to you, suspecting himself to have contracted the virus. Which test will you advise him to rule out/confirm his suspicion?

1. PCR
2. Routine urine examination
3. TLC
4. DLC

Answer. 1. PCR

Question 51. Match the following genes in column 1 with the insects that can be protected from with their coded proteins in column 2.

Column 1                    Column 2

a. cry I Ac                   (1) Cotton bollworm

b.cry I Ab                  (2) Beetles

c. Bt toxin gene        (3) Corn borer

1. a (1), b (3), c (2)
2. a (2), b (1), c (3)
3. a (1), b (2), c (3)
4. a (2), b (3), c (1)

Answer. 1. a (1), b (3), c (2)

Question 52. Which protein would you like to be produced by genetic engineering as cure for diseases such as emphysema?

1. α-1-Antitrypsin
2. Trypsin
3. Chymotrypsin
4. All of the above are required

Answer. 1. α-1-Antitrypsin

Question 53. “Rosie,” a transgenic cow, is known to produce a type of milk which has all the following characteristics, except

1. Protein content of 2.4 g/L
2. Has human a-lactalbumin
3. More balanced diet than normal cow milk for babies
4. Was produced for the first time in 2001

Answer. 4. Was produced for the first time in 2001

Question 54. According to the latest estimates, how many documented varieties of basmati rice are grown in India?

1. 30
2. 27
3. 118
4. 125

Answer. 2. 27

Question 55. Which ingredient was present in high concentrations in genetically modified (GM) rice as compared to the usual rice?

1. Protein
2. Carbohydrates
3. Na+ ions
4. Vitamin A

Answer. 4. Vitamin A

Question 56. Which of the following cannot be achieved using PCR?

1. Detect HIV in AIDS suspect.
2. Detect mutations in cancer patients.
3. Detect antigen-antibody interactions
4. Detect specific microorganisms from soil.

Answer. 3. Detect antigen-antibody interactions

Question 57. In electrophoresis, the separation of DNA fragments is based on

1. Charge
2. Mass only
3. Size
4. Both (1) and (3)

Answer. 4. Both (1) and (3)

Question 58. Pick the odd one out:

1. DNA microinjection
2. RNA interference
3. Retro virus mediated gene transfer
4. Embryonic stem cell mediated gene transfer

Answer. 2. RNA interference

Question 59. In xenotransplantation, a protein that causes graft rejection usually comes from transgenic

1. Cow
2. Mice
3. Pig
4. Sheep

Answer. 3. Pig

Question 60. Transgenics has provided many pharmaceuticals in their milk for the treatment of diseases. Which one of the following has not been a successful story?

1. Phenylketonuria
2. SCID
3. Emphysema (hereditary)
4. CFTR

Answer. 2. SCID

Question 61. Which is not true with respect to transgenic animals and their contribution to human welfare?

1. Transgenic mice are being tested to ensure safety of polio vaccine.
2. Rosie’s milk contained human gene insulin.
3. Transgenic cows produce milk with less lactose.
4. Transgenic sheep grow more wool.

Answer. 2. Rosie’s milk contained human gene insulin.

Question 62. An antibacterial compound that prevents mastitis in cows is

1. α-1-Antitrypsin
2. Lysostaphin
3. Lysozyme
4. Alginate lyase

Answer. 2. Lysostaphin

Question 63. Choose the incorrect statement with respect to bioweapons:

1. They are low-cost weapons.
2. They cause more casualties than conventional weapons.
3. They are extremely difficult to detect.
4. Bacterium E. coli created letter scare in 2001.

Answer. 4. Bacterium E. coli created letter scare in 2001.

Question 64. A set of standards by which a community regulates its behavior and activities in relation to the biological world is termed as

1. Biopatent
2. Biopiracy
3. Patent
4. Bioethic

Answer. 4. Bioethic

Question 65. Nexia Biotechnologies spliced spider genes into the cells of lactating

1. Cow
2. Sheep
3. Goat
4. None of these

Answer. 3. Goat

Question 66. Nif gene for nitrogen fixation in cereal crops such as wheat and jowar is introduced by cloning

1. Rhizobium meliloti
2. Bacillus thuringiensis
3. Rhizopus
4. Rhizophora

Answer. 1. Rhizobium meliloti

Question 67. VNTRS represent

1. New terminal regions in DNA
2. Functional genes in DNA
3. Split genes in sample DNA
4. Specific non-coding sequences with unique tandem repeats

Answer. 4. Specific non-coding sequences with unique tandem repeats

Question 68. Sheep Dolly was genetically similar to

1. The mother from which nucleated fertilized egg was taken
2. The mother from which the nucleus of udder cell was taken
3. The surrogate mother
4. Both surrogate mother and nuclear donor mother

Answer. 2. The mother from which the nucleus of udder cell was taken

Question 69. How does a bacterial cell protect its own DNA from restriction enzymes?

1. By adding methyl groups to adenines and cystosines.
2. By reinforcing bacterial DNA structure with covalent phosphodiester bonds.
3. By adding histones to protect the double-stranded DNA
4. By forming “sticky ends” of bacterial DNA to prevent the enzyme from attaching.

Answer. 1. By adding methyl groups to adenines and cystosines.

Question 70. All cells contain the same genetic information. Why cannot cells other than stem cells differentiate into various tissues?

1. As cells develop, their genetic makeup changes.
2. Stem cells are the only cells that can be implanted.
3. Stem cells are the only cells that do not have an X or Y chromosome and can, therefore, go into either a male or a female.
4. As cells develop, some genes are turned off permanently.

Answer. 4. As cells develop, some genes are turned off permanently.

Question 71. Polymerase chain reaction technology (PCR-technique) is used for

1. DNA identification
2. DNA repair
3. DNA amplification
4. Cleave DNA

Answer. 3. DNA amplification

Question 72. Which scientists obtained interferon through recombinant DNA technology?

1. Kohler and Milstein
2. Charles Weisman
3. Nathans and Smith
4. An American firm

Answer. 2. Charles Weisman

Question 73. When the genotype of an organism is improved by the addition of a foreign gene, the process is called

1. Tissue culture
2. Genetic diversity
3. Genetic engineering
4. Plastic surgery

Answer. 3. Genetic engineering

Question 74. A genetically manipulated organism containing in its genome one or more inserted genes of another species is called

1. Transposon
2. Gene expression
3. Transgenic organism
4. Retroposons

Answer. 3. Transgenic organism

Question 75. The use of transgenic plants as biological factories for the production of special chemicals is called

1. Molecular farming
2. Molecular genetics
3. Molecular mapping
4. Dry farming

Answer. 1. Molecular farming

Question 76. Which vector is commonly used in the transfer of gene in a crop plant?

1. Plasmids of B. subtilis
2. Bacteriophages
3. Ti plasmids of Agrobacterium
4. E. coli phages

Answer. 3. Ti plasmids of Agrobacterium

Question 77. The tumor inducing capacity of Agrobacterium tumaefaciens is located in large extrachromosomal plasmid called

1. Ti plasmid
2. Ri plasmid
3. Lambda phage
4. Plasmid pBR322

Answer. 1. Ti plasmid

Question 78. Genetic engineering aims at

1. Destroying wild gene
2. Preserving defective gene
3. Curing human disease by introducing new gene (hemophilia)
4. All the above

Answer. 3. Curing human disease by introducing new gene (hemophilia)

Question 79. Taq polymerase which is used in amplification of DNA is related with

1. Hybridoma technique
2. PCR technique
3. Gene cloning
4. rDNA technology

Answer. 2. PCR technique

Question 80. DNA fragments separated by gel electrophoresis are shown. Mark the correct statement:

1. Band 3 contains more positively charged DNA molecules than band 1.
2. Band 3 indicates more charge density than bands 1 and 2.
3. Band 1 has longer DNA fragment than bands 2 and 3.
4. All bands have equal length and charges but differ in base composition.

Answer. 3. Band 1 has longer DNA fragment than bands 2 and 3.

Question 81. Thermal cycle takes place in which technique?

1. Gel electrophoresis
2. PCR technique
3. Centrifugation
4. Southern blotting

Answer. 2. PCR technique

Question 82. Cry gene, which synthesizes crystal protein, is isolated from

1. Bacillus thuringiensis
2. Rhizobium
3. Bacillus polymyxa
4. Clostridium

Answer. 1. Bacillus thuringiensis

Question 83. Which of the following risks is associated with genetically modified food?

1. Toxicity
2. Allergic reaction
3. Antibiotic resistance in microorganisms present in alimentary canal
4. All of the above

Answer. 4. All of the above

Question 84. PCR technique is used in

1. Production of transgenic microbes
2. Production of genetically modified food
3. Forensic investigation
4. rDNA technique

Answer. 3. Forensic investigation

Question 85. TDF gene is a

1. Gene present on X-chromosome
2. Segment of RNA
3. Proteinaceous factor
4. Gene present on Y-chromosome

Answer. 4. Gene present on Y-chromosome

Question 86. BACS and YACs are

1. Natural DNA obtained from bacteria and yeast
2. Useful vectors for eukaryotic gene transfer
3. Artificial DNA obtained from bacteria and yeast
4. (2) and (3) both

Answer. 4. (2) and (3) both

Question 87. Gene therapy was first used in the treatment of

1. Albinism
2. Hemophilia
3. SCID
4. LIQID

Answer. 3. SCID

Question 88. DNA probe is used for

1. DNA fingerprinting
2. Detection of pathogenic bacteria
3. Medical genetics to find whether a person carries a particular gene or not
4. All of the above

Answer. 4. All of the above

Question 89. Bt cotton is resistant to

1. Roundworm
2. Flukeworm
3. Bollworm
4. Pinworm

Answer. 3. Bollworm

Question 90. A genetically engineered microorganism used successfully in the bioremediation of oil spills is a species of

1. Pseudomonas
2. Trichoderma
3. Xanthomonas
4. Bacillus

Answer. 1. Pseudomonas

Question 91. The first transgenic plant is

1. Potato
2. Tomato
3. Tobacco
4. Maize

Answer. 3. Tobacco

Question 92. Sheep Dolly was obtained by

1. Cloning the udder cell (somatic cell) fused with uninucleated oocyte
2. Cloning of gametes
3. Tissue culture
4. None

Answer. 1. Cloning the udder cell (somatic cell) fused with uninucleated oocyte

Question 93. E. coli are used in the production of

1. Rifampicin
2. LH
3. Ecdyson
4. Interferon

Answer. 4. Interferon

Question 94. A gaint rat is formed in the laboratory. What is the reason?

1. Gene mutation
2. Gene synthesis
3. Gene manipulation
4. Gene replication

Answer. 3. Gene manipulation

Question 95. The first cloned animal was

1. Dolly sheep
2. Polly sheep
3. Molly sheep
4. Dog

Answer. 1. Dolly sheep

Question 96. Introduction of food plants developed by genetic engineering is not desirable because

1. Economy of developing countries may suffer
2. These products are less tasty as compared to the already existing products
3. This method is costly
4. There is danger of introduction of viruses and toxins with introduced crop

Answer. 4. There is danger of introduction of viruses and toxins with introduced crop

Question 97. Which one of the following has found extensive use in genetic engineering work in plants?

1. Bacillus coagulans
2. Agrobacterium tumefaciens
3. Clostridium septicum
4. Xanthomonas citri

Answer. 2. Agrobacterium tumefaciens

Question 98. The maximum application of animal cell culture technology today is in the production of

1. Vaccines
2. Edible protein
3. Insulin
4. Interferon

Answer. 1. Vaccines

Question 99. Ti plasmid is often used for making transgenic plants. This plasmid is found in

1. Yeast as a 2-mm plasmid
2. Azotobacter
3. Rhizobium of the roots of leguminous plants
4. Agrobacterium

Answer. 4. Agrobacterium

Question 100. The cultivation of Bt cotton has been much in the news. Prefix “Bt” means

1. “Barium-treated” cotton seeds
2. “Bigger thread” variety of cotton with better tensile strength
3. Produced by “biotechnology” using restriction enzymes and ligases
4. Carrying an endotoxin gene from Bacillus thuringienisis

Answer. 4. Carrying an endotoxin gene from Bacillus thuringienisis

Question 101. An example of gene therapy is

1. Production of injectable hepatitis B vaccine
2. Production of vaccines in food crops such as potatoes which can be eaten
3. Introduction of gene for adenosine deaminase in persons suffering from severe combined immunodeficiency (SCID)
4. Production of test-tube babies by artificial insemination and implantation of fertilized eggs

Answer. 3. Introduction of gene for adenosine deaminase in persons suffering from severe combined immunodeficiency (SCID)

Question 102. Bacteria Pseudomonas is useful because of its ability to

1. Transfer genes from one plant to another
2. Decompose a variety of organic compounds
3. Fix atmospheric nitrogen in the soil
4. Produce a wide variety of antibiotics

Answer. 2. Decompose a variety of organic compounds

Question 103. Bacillus thuringiensis (Bt) strains have been used for designing novel

1. Bioinsecticidal plants
2. Bio-mineralization processes
3. Biofertilizers
4. Bio-metallurgical techniques

Answer. 1. Bioinsecticidal plants

Question 104. Which one of the following is a correct statement?

1. “Bt” in Bt-cotton indicates that it is a genetically modified organism produced through biotechnology.
2. Somatic hybridization involves the fusion of two complete plant cells carrying desired genes.
3. The anticoagulant hirudin is being produced from transgenic Brassica napus seeds.
4. “Flavr Savr” variety of tomato has enhanced the production of ethylene which improves its taste.

Answer. 3. The anticoagulant hirudin is being produced from transgenic Brassica napus seeds.

Question 105. The approximate number of genes contained in the genome of Kalpana Chowla was

1. 40,000
2. 30,000
3. 80,000
4. 1,00,000

Answer. 2. 30,000

Question 106. In transgenics, the expression of transgene in target tissue is determined by

1. Reporter
2. Enhancer
3. Transgene
4. Promoter

Answer. 4. Promoter

Question 107. Golden rice is a promising transgenic crop. When released for cultivation, it will help in

1. Alleviation of vitamin A deficiency
2. Pest resistance
3. Herbicide tolerance
4. Producing a petrol-like fuel from rice

Answer. 1. Alleviation of vitamin A deficiency

Question 108. Agrobacterium tumefaciens contains a large plasmid, which induces tumor in plants. It is termed as

1. Ti plasmid
2. Ri plasmid
3. Recombinant plasmid
4. Shine-Dalgarno sequence

Answer. 1. Ti plasmid

Question 109. Transgenic crops are modified through genetic engineering to develop natural resistance to insect pests. Which one is a transgenic plant?

1. Tobacco and cotton
2. Tomato and rice
3. Maize and sugarcane
4. Tomato and wheat

Answer. 1. Tobacco and cotton

Question 110. Genetically engineered human insulin is called

1. Humulin
2. Haematin
3. Hybriodoma
4. Hybrid

Answer. 1. Humulin

Question 111. Abzymes are

1. Abnormal enzymes
2. Enzymes acting on antibodies
3. Antibodies acting as enzymes
4. All of these

Answer. 3. Antibodies acting as enzymes

Question 112. Hybridoma technology was developed by

1. Taggart, 1982
2. Prie and Saxton, 1987
3. Vitella et. al., 1982
4. Kohler and Milstein

Answer. 4. Kohler and Milstein

Question 113. The technique for monoclonal antibody production was discovered by

1. Steward and Skoog
2. Arban and Haberlan
3. Kohler and Milstein
4. Lister and Koach

Answer. 3. Kohler and Milstein

Question 114. The first clinical gene therapy was given for treating

1. Both sense and anti-sense RNA
2. A particular hormone
3. An antifeedant
4. A toxic protein

Answer. 1. Both sense and anti-sense RNA

Question 115. Tobacco plants resistant to nematode have been developed by the introduction of DNA that produced (in the host cells)

1. Diabetes mellitus
2. Chicken pox
3. Rheumatoid arthritis
4. Adenosine deaminase deficiency

Answer. 4. Adenosine deaminase deficiency

Question 116. Which of the following Bt crops is being grown in India by the farmers?

1. Cotton
2. Brinjal
3. Soybean
4. Maize

Answer. 1. Cotton

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 91. Assertion: RNAi takes place in all eukaryotic organisms as a method of cellular defense.

Reason: Complementary dsRNA molecule binds to specific mRNA and prevents its translation (silencing).

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 92. Assertion: Bt toxin is a protein crystal containing insecticidal protein.

Reason: B. thuringiensis forms these protein crystals continuously throughout its growth period.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 93. Assertion: Recombinant DNA technology has been less effective in therapeutic drug production.

Reason: Recombinant therapeutics induces unwanted immunological responses.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 94. Assertion: Transgenic mice are being used to test the safety of the polio vaccine.

Reason: It could replace the use of monkeys to test the safety of batches of the vaccine.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 95. Assertion: Indian Government has set up organizations such as GEAC (Genetic Engineering Approval Committee), which will make decisions regarding the validity of GM research and the safety of introducing GM organisms for public services.

Reason: Genetic modification of organisms can have unpredictable results when such organisms are introduced into the ecosystem.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

BioTechnology: Principles And Processes

Principles Of Biotechnology

• Biotechnology can be broadly defined as “using living organisms or their products for commercial purposes.”
• As such, biotechnology has been practiced by human society since the beginning of recorded history in activities such as baking bread, brewing alcoholic beverages, and breeding food crops or domestic animals.
• A narrower and more specific definition of biotechnology is “the commercial application of living organisms or their products, which involves deliberate manipulation of their DNA molecules.”
• This definition implies a set of laboratory techniques developed within the last 20 years that have been responsible for the tremendous scientific and commercial interest in biotechnology.
• Some other available definitions of biotechnology are as follows:
  • “The application of biological organisms, systems, or processes to manufacturing and service industries.” British Biotechnologist
  • “The integrated use of biochemistry, microbiology, and genetic engineering sciences in order to achieve technological (industrial) application of capabilities of microorganisms, cultured tissue cells, and parts thereof.”-European Federation of Biotechnology
  • “Controlled use of biological agents such as microorganisms and cellular components for beneficial use.” US National Science Foundation
• The development of biotechnology can be studied considering its growth that occurred in two phases: (a) Traditional (old) biotechnology and (b) new (modern) biotechnology.

Read and Learn More NEET Biology Notes

Traditional Biotechnology

• Traditional biotechnology includes processes that are based on the natural capabilities of microorganisms.
• It is also called conventional technology; it has been used for many centuries.
• Curd; vinegar; ghee; wine, beer, and other alcoholic beverages; and idli, dosa, cheese, paneer, and some other foods have been produced using traditional bio-technology.
• In Indian Ayurveda, the production of asva, arista, etc., is done through traditional biotechnology.
• According to some people, traditional biotechnology is, therefore, an art rather than a science.

Modern Biotechnology

• When extremely new and useful traits in crop varieties and animal breeds are created with the help of genetic engineering, it is called modern biotechnology.
• It was developed in 1970.
• For example, in vitro fertilization leading to a “test tube baby,” synthesizing a gene and using it, developing a DNA vaccine, or correcting a defective gene are all parts of modern biotechnology.
• Among many, the two main techniques that gave birth to modern biotechnology are as follows:
  • Genetic engineering: The techniques which change the chemistry of genetic material (DNA and RNA) to introduce these into host organisms and, thus, alter the phenotype of the host organism are called genetic engineering (recombinant DNA technology).
  • To maintain microbial contamination-free (sterile) surrounding in chemical engineering: Due to such type of maintenance, only desired microorganisms/cells will be formed in large number for the manufacture of biotechnological products such as antibiotics, vaccines, enzymes, hormones, and blood clotting factors. It is essential to have complete aseptic conditions.

Concept of Genetic Engineering

• Combining DNA from different existing organisms such as plants, animals, and bacteria results in modified organisms with a combination of traits from the parents.
• This sharing of DNA information occurs naturally through sexual reproduction and has been exploited in plant and animal breeding for a number of years.
• However, sexual reproduction (recombination) can occur between the individuals of same species. Genetic engineering is the manipulation of prokaryotic as well as eukaryotic DNA.
• It involves the breakage of a DNA molecule at two de- sired places to isolate a specific DNA segment which is then inserted in another DNA molecule at a desired position.
• The product, thus, obtained is called recombinant DNA and the technique is often called genetic engineering.
• The cutting of the DNA at specific locations became possible by so called “molecular scissors,” i.e., restriction enzymes.
• In chromosomes, there is a specific “ori” site or the origin of replication which initiates the replication.
• Therefore, for the duplication of any foreign DNA in an organism, it should be linked with the ori sites so that the foreign DNA can duplicate and multiply within the organism.
• This is called gene cloning. Multiple copies of any template DNA can be produced by using gene cloning.
• The construction of the first recombinant DNA emerged from the possibility of linking a gene encoding antibiotic resistance with a native plasmid (autonomously replicating circular extra-chromosomal DNA) of Salmonella typhimurium.
• Stanley Cohen and Herbert Boyer accomplished this in 1972 by isolating the antibiotic resistance gene by cutting out a piece of DNA from a plasmid which was responsible for conferring antibiotic resistance.
• These plasmid DNA molecules act as vectors to transfer the piece of DNA attached to it.
• As mosquito acts as an insect vector to transfer the malarial parasite into human body, in the same way, a plasmid can be used as a vector to deliver an alien piece of DNA into the host organism.
• The linking of antibiotic resistance gene with the plasmid vector became possible with enzyme DNA ligase, which acts on cut DNA molecules and joins their ends.
• This makes a new combination of circular autonomously replicating DNA created in vitro known as recombinant DNA.
• When this DNA is transferred into Escherichia coli, a bacterium closely related to Salmonella, it replicates using the new host’s DNA polymerase enzyme and makes multiple copies.
• The ability to multiply copies of antibiotic resistance gene in E. coli was called cloning of antibiotic resistance gene in E. coli.
• Therefore, there are three basic steps in genetically modifying an organism:
  • Identification of DNA with desirable genes.
  • Introduction of the identified DNA into the host.
  • Maintenance of introduced DNA in the host and transfer of the DNA to its progeny.

Tools Of Recombinant DNA Technology

The technology or genetic engineering involves restriction enzymes, ligase enzymes, polymerase enzymes, vectors, and the host organism.

Restriction Enzymes

• In the late 1960’s, scientists Stewart Linn and Werner Arber isolated samples of two types of enzymes responsible for phage growth restriction in E. coli bacteria.
• One of these enzymes was methylated DNA while the other was cleaved unmethylated DNA at a wide variety of locations along the length of the molecule. The first type of enzyme was called methylase while the other was called restriction nuclease.
• These enzymatic tools were important for scientists who were gathering the tools needed to “cut and paste” DNA molecules.
• What was needed now was a tool that would cut DNA at specific sites, rather than at random sites along the length of the molecule, so that scientists can cut DNA- molecules in a predictable and reproducible way.

Site-Specific Nuclease

• This important development came when H.O. Smith, K.W. Wilcox, and T.J. Kelley isolated and characterized the first restriction nuclease whose functioning depended on a specific DNA nucleotide sequence.
• Working with Haemophilus influenzae bacteria, this group isolated an enzyme called Hind II that always cut DNA molecules at a particular point within a spe- cific sequence of six base pairs.
• This sequence is
  • 5′ GT (pyrimidine: T or C) (purine: A or G) AC 3′
  • 3′ CA (purine: A or G) (pyrimidine: T or C) TG 5′
• They found that Hind II enzyme always cuts directly in the center of this sequence.
• Wherever this particular sequence of six base pairs occurs unmodified in a DNA molecule, Hind II will cleave both DNA strands or backbones between the third and the fourth base pairs of the sequence.
• Moreover, Hind II will cleave both DNA strands or backbones between the third and the fourth base pairs of the sequence will only cleave a DNA molecule at this particular site. For this reason, this specific base sequence is known as the “recognition sequence” for Hind II.
• Hind II is just one example of the class of enzymes known as restriction nucleases.
• In fact, more than 900 restriction enzymes, some sequences specific and some not, have been isolated from over 230 strains of bacteria since the initial discovery of Hind II.
• These restriction enzymes generally have names that reflect their origin.
• The first letter (in italics) of the name comes from the genus and the second two letters (in italics) come from the species of the prokaryotic cell from which they were isolated.
• Next is the strain of the organism and last is the Roman numeral indicating the order of discovery (the order in which the enzymes were isolated from single strains of bacteria).
• For example, Eco RI comes from Escherichia coli RY strain (and was the first endonuclease isolated from bacteria) while Hind II comes from Haemophilus in- fluenzae strain Rd.
• Nucleases are further described by the addition of the prefix “endo” or “exo” to the name. The term “endonuclease” applies to sequence-specific nucleases that break nucleic acid chains somewhere in the interior, rather than at the ends of the molecule.
• Nucleases that function by removing nucleotides from the ends of the molecules are called exonucleases.
• Three main classes of restriction endonucleases: type 1, type 2, and type 3, have been described, each distinguished by a slightly different mode of action.
• Out of these three types, type 1 and type 3 restriction enzymes are not used in recombinant DNA technology.
• Type 2 restriction enzymes are used in recombinant DNA technology, because they can be used in vitro to recognize and cut within the specific DNA sequence typically consisting of 4-8 nucleotides.
• Type 1 enzymes recognize specific sites within the DNA but do not cut at these sites.
• Hence, heterogeneous population of DNA fragments is produced. Therefore, type 1 enzymes do not take part in the technology. Type 3 enzymes recognize a specific sequence of DNA molecule. Thus, the products of type 3 enzymes are homogeneous population of DNA fragments; so, they cannot be used for genetic engineering experiments.
• The DNA segments cut by restriction enzymes are palindromic, i.e., the nucleotide sequences of these DNA pieces read the same both backwards and forward when the orientation of reading is kept same, e.g., madam.
• Blunt or flush ends are produced by many restriction enzymes which cleave both strands of DNA at exactly the same nucleotide position-in the center of recognition site. For example, Small recognizes six-nucleotide palindromic sequence.
• It cuts both DNA strands producing blunt ends.
• Sticky or cohesive ends are produced when restriction enzymes do not cut DNA at the same nucleotide position but cut the recognition sequence unequally. This produces short, single-stranded overhangs at each end. These are known as sticky ends. For example, Eco RI recognizes 6-nucleotide palindromic sequence.

• This restriction endonuclease cuts both DNA strands unequally, producing 5′ overhangs of four nucleotides.
• The stickiness helps enzyme ligase to make the DNA pieces join.

Other Enzymes Used in Recombinant DNA Technology

• In addition to restriction enzymes, there are several other enzymes that play an important role in DNA technology.
• Three of the important ones are DNA ligase, alkaline phosphatase, and DNA polymerase.
  • DNA ligase: This enzyme forms phosphodiester bonds between adjacent nucleotides and covalently links two individual fragments of double-stranded DNA. The action of ligase enzyme requires a phosphate group at the 5′ carbon of one nucleotide and a hydroxyl group at the 3′ carbon of the adjacent nucleotide to form phosphodiester bond between these two nucleotides. The enzyme used most often in the rDNA technology is T4 DNA ligase, which is encoded by phage T4.
  • Alkaline phosphatase (AP): As mentioned above, ligation absolutely requires the presence of 5′ phosphate group at the DNA site to be ligated. If this phosphate group is removed, this DNA can- not be ligated. The enzyme alkaline phosphatase is used to remove the phosphate group from the 5′ end of a DNA molecule, leaving a free 5′ hy- droxyl group. This enzyme can be isolated from bacteria (BAP) or calf intestine (CAP). It is used to prevent unwanted self-ligation of vector DNA molecules in the procedures of rDNA technology.
    However, the ligation of the vector to the insert can occur as the insert still has its 5′ phosphate.
  • DNA polymerase: DNA polymerase I (DNA Pol I) enzyme polymerizes DNA synthesis on DNA template or complementary DNA (cDNA). It also catalyzes 5′ 3′ and 3′ 5′ exonucleolytic degradation of DNA. The other two enzymes are DNA Pol II and DNA Pol III. These have almost similar catalytic activity. DNA Pol III is about several times more active than the other two. Where there is preformed DNA template, it pro- duces a parallel strand in the presence of ATP.

Separation and Isolation of DNA Fragments

• After the cutting of DNA by restriction enzymes, fragments of DNA are formed.
• These fragments can be separated by a technique called gel electrophoresis.
• Electrophoresis is a technique of separation of charged molecules under the influence of an electrical field so that they migrate in the direction of the electrode bearing opposite charge, i.e., positively charged molecules move towards cathode (-ve electrode) and negatively charged molecules travel towards anode (+ve electrode), through a medium/matrix.
• This technique was developed by A. Tiselius in 1937.
• Nowadays, the most commonly used matrix is agarose which is a polysaccharide extracted from sea weeds.
• DNA fragments separate according to size through the pores of agarose gel.
• Hence, the smaller the fragment size, the farther it moves.
• Agarose dissolves in hot water. When this solution is cooled, double helices form. These become arranged laterally and produce thick filaments.
• These filaments become cross-linked to form the gel.
• Pore size depends on agarose concentration.

• Separated DNA fragments can be seen only after staining the DNA with a compound ethidium bromide followed by exposure to UV radiations as bright orange colored bands. The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. This step is called elution. Several techniques are used for eluting the DNA from the gel piece. These purified DNA fragments are used in the formation of recombinant DNA by linking them with cloning vectors.

• Cloning vectors: Another important tool for genetic engineering is the vehicle for cloning, called vector. A vector carries a foreign DNA sequence into a given host cell. Bacterial plasmids and bacteriophages are considered the most useful. This is because of the following reasons:
  • These are independent of the control of chromosomal DNA.
  • Bacteriophage genomes occur in very large numbers in bacterial cells.
  • The copies of plasmids per cell range from only a few to hundred or even more.

• Certain essential features should be present in a DNA molecule to act as a cloning vector.
  • Origin of replication (ori): This is a DNA sequence which serves as a starting point for replication. When a DNA fragment gets associated with ori, foreign DNA into the vector would also replicate inside the host cell. Some vectors possess origin which favors the formation of high copy numbers and, hence, are preferred.
  • Selectable marker: A vector should also include a selectable marker. This is a gene which would permit the selection of host cells containing vector from amongst those which do not possess vector. Common selectable markers include genes encoding antibiotic resistance such as ampicillin resistance or enzymes such as ẞ-galactosidase (product of lac Z gene of lac operon). These genes can be identified by a color reaction.
  • Recognition sites: A vector should possess a unique restriction site that would allow a particular enzyme to cut the vector only once. This site would be recognized by the commonly used restriction enzymes. If there are more than one recognition sites in a vector, several fragments would be produced. Generally, the vectors used possess unique recognition sites for several restriction enzymes in a small region of DNA. This is known as polylinker or multiple cloning site (MCS). Such cloning site offers a choice of restriction enzymes. Unique restriction endonuclease recognition site enables the insertion of foreign DNA into the vector for the production of recombinant DNA. The foreign DNA is inserted and made to join (ligate) at a specific restriction site, generally, in antibiotic resistance gene.
  • pBR322 has genes for resistance against two antibiotics (tetracycline and ampicillin). An origin of replication and a variety of restriction sites for cloning of restriction fragments are obtained through cleavage with a specific enzyme. Foreign DNA is inserted at a site located in one of the two genes for resistance against antibiotics, so that it will inactivate one of the two resistance genes.
  • The insert bearing plasmids can be selected by their ability to grow in a medium containing only one of the two antibiotics and their failure to grow in a medium containing both antibiotics. The plasmids carrying no insert, on the other hand, will be able to grow in a media containing one or both antibiotics. In this way, the presence of resistance genes against ampicillin and tetracycline allows the selection of Escherichia coli colonies transformed with plasmids carrying the desired foreign cloned DNA fragment.
  • Size of the vector: The cloning vector should be small in size. Large molecules have a tendency to break down during purification. These are also difficult to manipulate.

Different Types Of Vectors

Several types of vectors satisfying the above characters have been developed. The following are some of the commonly used vectors.

Plasmids

• These are extra-chromosomal, non-essential self-replicating, usually circular, and double-stranded DNA molecules occurring in some bacteria and also a few yeasts.
• Some of the characters carried by plasmids may not be required for normal bacterial metabolism but may be of great advantage, e.g., antibiotic resistance.
• pBR322 is one of the standard cloning vectors widely used in gene cloning experiments.
• This vector has been restructured by inserting genes for antibiotic resistance.
• It is named after Boliver and Rodriguez who prepared this vector.

• PUC (named after the University of California) is another such reconstructed plasmid vector.
• The vectors mentioned above are able to replicate only in E. coli.
• Therefore, many vectors constructed for eukaryotic cells are also functional in E. coli.
• These vectors are called shuttle vectors.
• The vectors contain two types of origin of replication and selectable marker genes one for the eukaryotic cell and the other for E. coli.
• The common example of this type is yeast episomal plasmid (Yep).
• In plants, tumor-inducing (Ti) plasmid of bacterium Agrobacterium tumfaciens has been modified to function as a vector.

Vectors Based on Bacteriophages

Bacteriophages are viruses which infect bacterial cells, produce new phages inside the host bacterium, and are released from the host cell to again infect other bacterial cells. M13 and lambda (2) phages are in common use.

Cosmids

Cosmids combine some features of plasmid and cos (cohesive end sites) of phage lambda (cosmid = cos + plasmid).

Yeast Artificial Chromosome Vectors

Yeast artificial chromosome (YAC) contains telomeric sequence, centromere, and autonomously replicating sequence from yeast chromosomes. It also has suitable restriction enzyme sites and genes useful as selectable markers.

Bacterial Artificial Chromosome Vectors

• Bacterial artificial chromosome (BAC) is based on the F-plasmid (fertility) of E. coli. It contains genes for the replication and maintenance of F-factor, selectable marker, and cloning sites.
• Color reaction: Due to the inactivation of antibiotics, the selection of recombinants becomes a burdensome process because it requires simultaneous plating on two plates having different antibiotics. Thus, an alternative selectable marker is developed to differentiate recombinants and non-recombinants on the basis of their ability to produce color in the presence of a chromogenic substance. Now, a recombinant DNA is inserted in the coding sequence of enzyme ẞ-galac-tosidase. This causes the inactivation of the enzyme; it is called insertional inactivation. If the plasmid in the bacterium does not have an insert, the presence of a chromogenic substrate gives blue-colored colonies. The presence of insert results in the insertional inac- tivation of B-galactosidase. Therefore, the colonies do not produce any color. These colonies are marked as recombinant colonies.

Vectors for Cloning Genes in Plants and Animals

• We know the procedure of transferring genes into plants and animals from bacteria and viruses.
• The procedure to transfer genes to transform eukaryotic cells and force them to do what the bacteria or viruses require is also known.
• For example, Agrobacterium tumifaciens, a pathogen (disease causing agent) of several dicot plants, is able to transfer a piece of DNA known as T-DNA to convert normal plant cells into tumor and direct these tumor cells to secrete the chemicals required by the pathogen. Similarly, retroviruses (cause leukosis or sarcoma types of cancer) in animals including humans are able to change normal cells into cancerous cells.
• The Ti plasmid of Agrobacterium tumifaciens has been modified into a cloning vector which is not pathogenic to plants. However, it is still able to use the procedure to deliver genes of our interest into various plants.
• Similarly, retroviruses are used to carry desirable genes into animal cells.
• Thus, once a gene or DNA fragment is joined to a suitable vector, it is transferred into a bacterial plant or animal host where it undergoes multiplication.

Host Cell

• Competent host cell is required for transformation with recombinant DNA.
• After the formation of recombinant DNA, propagation of it must occur inside a living system or a host.
• Different types of available host cells are E. coli, yeast, and animal and plant cells.
• The type of host cell to be used depends on the aim of cloning experiment.
• Eukaryotic cells will be the preferred host for the expression of some eukaryotic proteins.
• Yeast cells are preferred because these are the simplest eukaryotic organisms and, like bacteria, are single celled, genetically well characterized, and easy to grow and manipulate.
• Plant and animal cells can be used for protein expression either in tissue culture or as cells in the whole organism to create genetically modified (GM) crops and animals.
• As DNA is a hydrophilic molecule, it cannot pass through cell membrane.
• Therefore, the bacterial cells should be capable of up- taking DNA.
• This is accomplished by treating them with specific concentration of a divalent cation, e.g., Ca2+, making them competent which causes an efficient entry of DNA into the bacterium through the pores in its cell wall.
• Recombinant DNA can be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 42°C (heat shock), and then putting them back on ice. As a result, bacteria get enabled to pick up recombinant DNA.
• There are other methods to introduce foreign DNA into host cells. These are briefly described in the following subsections.

Microinjection

• In the microinjection method, the recombinant DNA is directly injected into the nucleus of animal cell by using micro-needles or micro-pipettes. It is used in oocytes, eggs, and embryo. Jeffey S. Chamberlain et. al. (1993) of Human Genome Center, Michigan University, USA, have cured mice that inherited a neuromuscular disease which is like the muscular dystrophy of humans.

Direct DNA Injection

Direct injection of DNA into skeletal muscle led to the possibility of using gene as vaccines. Due to low level of expression, therapeutic benefits for the treatment of genetic disorder could not be derived. This method gave birth to the concept of DNA vaccine or genetic immunization.

Gene Gun or Biolistics

New technologies such as gene gun are also available for vector-less direct gene transfer. DNA coated onto microscopic pellets is literally shot into target cells. Although it is developed for plants, it is also used for animal cells for promoting tissue repair or reducing healing time. This method made great impact in the field of vaccine development.

Process Of Recombinant DNA Technology

Recombinant technology is a complicated process. Several steps lead to the desired goal. The major steps are as follows:

• Isolation of DNA
• Digestion of DNA by restriction endonuclease enzyme
• Gene amplification
• Introduction of recombinant DNA into host cells.
• Identification of recombinants
• Gene product manufacture
• Processing

Isolation of DNA: Isolation of the Genetic Material (DNA)

• Nucleic acid (DNA or RNA) is the genetic material of all organisms. It is DNA in majority of organisms.
• For cutting the DNA with restriction enzymes, it needs to be pure and free from other macromolecules.
• Because DNA is covered with membranes, it has to break the cell open to release DNA and other macro-molecules such as RNA, proteins, polysaccharides, and lipids.
• It is obtained by treating the bacterial cells/plant or animal tissues with enzymes such as lysozyme (bacteria), cellulase (plant cells), and chitinase (fungus).
• As we know that genes are present on long molecules of DNA intertwined with proteins such as histones, RNA can be removed by treating with ribonuclease while proteins can be removed by treating with protease.
• Other molecules are removed by proper treatments. Purified DNA finally precipitates out after the addition of chilled ethanol.
• This is seen as a collection of fine threads in suspension.

DNA Digestion by Restriction Enzymes

• The vector and the target DNA fragment can be separately digested with the same restriction enzyme.
• The digested vector and the target DNA fragment are then incubated together in the presence of DNA ligase enzyme.

• Incubation results in bonding of two types of DNA by phosphodiester bonds between them.
• Thus, the deoxyribose-phosphate backbones of vector molecule and the target DNA fragment are covalently linked, forming a recombinant DNA molecule.
• Another possibility in this experiment is the rejoining of the sticky ends of the vector molecule itself, forming a circular vector DNA molecule that is without foreign DNA molecule.
• This possibility is eliminated by treating digested vector with alkaline phosphatase or by using different restriction enzymes.

Gene Amplification

• Gene amplification is the process of selective multiplication of a specific region of DNA molecule.
• The process has also been used to produce DNA fragments for cloning.
• Amplification is achieved by a special method known as polymerase chain reaction (PCR) developed by Kary Mullis in 1985 for which he shared Nobel Prize in 1993.
• The principle underlying the technique is to heat double-stranded DNA molecule to a high temperature so that the two DNA strands separate into single-stranded DNA molecules.
• If these single-stranded molecules are copied by a DNA polymerase, it would lead to the duplication of the original DNA molecule; if these events are repeated many times, then multiple copies of the original DNA sequence can be generated.
• The basic requirements of a PCR reaction are as follows:
  • DNA template: Any source that contains one or more target DNA molecules to be amplified can be taken as a template.
  • Primers: Primers, which are oligo-nucleotides, usually 10-18 nucleotides long, hybridize to the target DNA region, one to each strand of the double helix. Two primers are required and these primers are oriented with their ends facing each other, allowing the synthesis of the DNA towards one another.
  • Enzyme: DNA polymerase which is stable at high temperatures (>90°) is required to carry out the synthesis of new DNA. The polymerase which is generally used in PCR reactions is Taq polymerase (isolated from bacterium Thermus aquaticus). Other thermostable polymerases can also be used.

Working Mechanism of PCR

• A single PCR amplification cycle involves three basic steps: denaturation, annealing, and extension (polymerization).
  • Denaturation: In the denaturation step, the tar- get DNA is heated to a high temperature (usually 94°C), resulting in the separation of the two strands. Each single strand of the target DNA then acts as a template for DNA synthesis.
  • Annealing: In this step, the two oligo-nucleotide primers anneal (hybridize) to each of the single- stranded template DNA since the sequence of primers is complementary to the 3′ ends of template DNA. This step is carried out at a lower temperature depending on the length and sequence of the primers.
  • Primer extension (polymerization): The final step is extension, wherein Taq DNA polymerase (of a thermophilic bacterium Thermus acquaticus) synthesizes the DNA region between the primers, using dNTPs (deoxynucleoside triphosphates) and Mg2+. It means the primers are extended towards each other so that the DNA segment lying between the two primers is copied. The optimum temperature for this polymerization step is 72°C. To begin the second cycle, the DNA is again heated to convert all newly synthesized DNA into single strands, each of which can now serve as a template for the synthesis of more new DNA. Thus, the extension product of one cycle can serve as a template for subsequent cycles and each cycle essentially doubles the amount of DNA from the previous cycle. As a result, from a single template molecule, it is possible to generate 2″ molecules after n number of cycles.

Application of PCR

Some of the areas of application of PCR are briefly mentioned here.

• Diagnosis of pathogens: Pathologists use techniques based on detecting specific enzymes or antibodies against disease-related proteins. But these techniques cannot be used for detecting infectious agents that are difficult to culture or that persist at very low levels in infected cells. To overcome these problems, PCR-based assays have been developed that detect the presence of gene sequences of infectious agents.
• Diagnosis of specific mutation: PCR can be used to detect the presence of a specific mutation that is r sponsible for causing a particular genetic disease be- fore the actual onset of the disease. By using PCR, phenylketonuria, muscular dystrophy, sickle-cell anemia, AIDS, hepatitis, Chlamydia, and tuberculosis can be diagnosed.
• DNA fingerprinting: PCR is of immense value in generating abundant amount of DNA for analysis in the DNA fingerprinting technique used in forensic science to link a suspect’s DNA to the DNA recovered at a crime scene.
• Detection of specific microorganisms: PCR is also used for detecting specific microorganisms from the environment samples of soil, sediments, and water.
• In prenatal diagnosis: It is useful to detect a genetic disease in fetus before birth. If the disease is not curable, abortion is recommended.
• Diagnosis of plant pathogens: Many diseases of plants can be detected by using PCR. For example, viroids (associated with apple, grape, citrus, pear, etc.), viruses (such as TMV and bean yellow mosaic virus), bacteria, mycoplasmas, etc.
• In paleontology: PCR is used to clone the DNA fragments from the mummified remains of humans and extinct animals such as wooly mammoth and dinosaurs.

Introduction of Recombinant DNA into Host Cells

• Once the recombinant DNA molecule has been multiplied, it needs to be inserted into host cells.
• Many methods for introduction are available.
• The selection of a method depends upon the type of vector and the host cell along with other things.
• Some common methods are as follows:
  • Transformation: This is a method where cells take up DNA from their surroundings. Since many cells such as those of E. coli, yeast, and mammals do not naturally absorb DNA, they need to be made competent. Mandel and Higa (1970) observed that E. coli cells can be made competent to take up external DNA by suspending them in cold calcium chloride.

• • Transfection: In this method, DNA is mixed with charged substances such as calcium phosphate and cationic liposomes. These are spread on the recipient host cells. Calcium ions carry foreign DNA and release it inside the cell since calcium gets precipitated in the form of calcium phosphate, thus, transferring the DNA by endocytosis.
  • Microinjection and macroinjection: Specially designed micromanipulator is used to inject DNA into cytoplasm or the nucleus of a recipient cell or protoplast. The method is used for the direct introduction of DNA into plant or animal cells without using special eukaryotic vectors.

• • Microprojection (biolistics or particle gun): Tungsten or gold particles (microparticles) coated with DNA are accelerated to a very high initial velocity. These microprojectiles are carried by other (nylon) microprojectiles or the bullet, causing them to penetrate the cell walls of intact target cells or tissues.

• • Electroporation: Short electrical impulses of high field strength are given. These increase the permeability of protoplast membrane by creating transient microscopic pores, thus, making the entry of DNA molecules into the cells much easier.
  • Ti plasmid based gene transfer:
    • A more common method of introducing foreign DNA into plant cells is to use the bacterium Agrobacterium tumefaciens and its Ti plasmid.
    • This Gram-negative soil bacterium is a plant pathogen and produces crown gall disease in many dicotyledons including grapes, stone fruits, roses, tomato, sunflower, cotton, soybean, etc.
    • Most strains of this bacterium carry Ti plasmid.
    • In nature, Agrobacterium attaches to the leaves of plants and Ti plasmid is transferred into plant cells.
    • The plasmid becomes incorporated into plant chromosomal DNA.
    • Therefore, Ti plasmid has been used as a vehicle for the introduction of recombinant DNA into plant cells.
    • Ti plasmids cause tumors in plants.
    • Strains of the bacterium have been developed which do not have tumor-inducing genes. However, the T-region of plasmid plays an important role in gene transfer.
    • This specific segment of bacterial plasmid DNA is called T-DNA (transferred DNA).
    • T-DNA has a cloning site into which foreign DNA (DNA insert) is inserted.
    • This recombinant plasmid is now introduced into bacterium Agrobacterium tumefaciens. It is then used to infect cultured cells.
    • The T-region of the plasmid with foreign DNA (or DNA insert) is transferred to plant cells.
    • It gets integrated with the chromosomal DNA of the cell.
    • Cultured cells are induced to grow into plantlets.
    • These are planted into the soil where mature plants are formed.

Identification of Recombinant

• After the insertion of recombinant DNA into the host cell, these need to be identified from those which do not possess it.
• The methods used to do so consider expression or non- expression of certain characters especially antibiotic resistance gene (e.g., ampicillin resistance gene) on plasmid vector.
• Selectable marker usually provides resistance against a substrate which when added to the culture medium inhibits the growth of normal cells or tissues in culture, so that only transformed tissues will grow.

• Thus, the simplest method for identification is to grow transformed host cells (with ampicillin resistance gene) on medium containing ampicillin.
• This would enable the cells containing this trans- formed plasmid to grow and form colonies.
• There are other methods for the detection of recombinants based on the fact that the cloned DNA fragment disturbs the coding sequence of gene.
• This is known as insertional inactivation.
• Let us consider a plasmid containing genes resistant for two different antibiotics: ampicillin and tetracycline.
• If the target DNA fragment is inserted in a site located in ampicillin resistance gene, this gene will then be in-activated.
• Thus, host cells with such a recombinant plasmid will be sensitive to ampicillin but resistant to tetracycline.
• These host cells will die when grown on ampicillin containing medium but would grow on medium containing tetracycline.
• Self-ligated or religated (non-recombinant) vectors would grow on medium containing both ampicillin and tetracycline, being resistant to them.
• Another, but similar, method involves insertional inactivation of the lac Z gene.
• It is known as blue-white selection, being color based.

Gene Product Manufacture

• When recombinant DNA is transferred into a bacterial, plant, or animal cell, the foreign DNA is multiplied.
• Most of the recombinant technologies are aimed to produce a desirable protein.
• So, there is a need for expression recombinant DNA. After the cloning of the gene of interest, one has to maintain the optimum conditions to induce the expression of the target protein and consider producing it on a large scale.
• If any protein encoding gene is expressed in a heterologous host, it is known as a recombinant protein.
• The cells having cloned genes of interest can be grown on a small scale in the laboratory.
• Cultures may be used for extracting and purifying the desired protein.
• The cells can also be multiplied in a continuous system where the used medium is passed out from one side and the fresh medium is added from the other side to maintain the cells in their physiologically most active lag exponential phase (lag phase: no significant increase of cells; exponential phase: rapid multiplication of cells).
• This type of culturing method produces a larger biomass to get higher yields of the desired protein.
• Small volume cultures cannot give large quantities of products.
• To produce large quantities of these products, the development of bioreactors is required where large volumes (100-1000 L) of culture can be processed. Hence, bioreactors are like vessels in which raw materials are biologically converted into specific products (individual enzymes) using microbial, plant, animal, or human cells.
• A bioreactor provides the optimal conditions for obtaining the desired product by providing optimum growth conditions such as substrate, temperature, pH, vitamins, oxygen, and salts.
• One of the most commonly used bioreactor is of stirring type.
• A stirred reactor is usually cylindrical with a curved base to allow mixing of the contents of the reactor.
• The presence of stirrer makes mixing possible and also makes oxygen available through the reactor.
• A bioreactor also has an agitatory system, an oxygen delivery system, a foam control system, a temperature control system, pH control system, and sampling ports so that small volumes of culture can be withdrawn periodically.

Downstream Processing

• Once the product is ready, it has to be processed for commercial use.
• This requires purification and strict quality control to maintain the efficacy.
• The products based on biotechnology must ensure that they satisfy the consumer needs and are not harmful.
• Therefore, a thorough checking of products at each level of manufacture is done.
• The manufacturing process and the quality control methods vary with each product.

Choose the correct answer:

Question 1. 3′-5′ exonucleolytic degradation of DNA is performed by which enzyme?

1. DNA polymerase
2. Alkaline phosphatase
3. DNA ligase
4. RNA polymerase

Answer. 1. DNA polymerase

Question 2. The technique of gel electrophoresis was developed by

1. Kary Mullis
2. J.S. Chamberlain
3. A. Tiselius
4. F. Sanger

Answer. 3. A. Tiselius

Question 3. Which of the following dyes can be used to visualize nucleic acid after electrophoresis?

1. Acridine orange
2. Ethidium bromide
3. Bromophenol blue
4. Both (1) and (2)

Answer. 4. Both (1) and (2)

Question 4. Which of the following bonds are formed by the action of DNA ligase?

1. Sugar-phosphate bond
2. Phosphodiester bond
3. Both (1) and (2)
4. Phosphate-phosphate bond

Answer. 3. Both (1) and (2)

Question 5. Who were responsible for the isolation of “methylase” kind of enzyme from E. coli in 1960’s?

1. Cohen and Boyer
2. Banting and Best
3. Linn and Arber
4. Smith and Wilcox

Answer. 3. Linn and Arber

Question 6. The specific sequence recognized by “molecular scissors” is called

1. Isomer
2. Isobar
3. Misnomer
4. Palindrome

Answer. 4. Palindrome

Question 7. When a piece of DNA is digested with Eco RI, what kind of ends are created?

1. Blunt ends
2. Flush ends
3. Cohesive ends
4. Non-staggered ends

Answer. 3. Cohesive ends

Question 8. The sticky ends generated by the action of Eco RI on insert DNA facilitate the action of which enzyme?

1. DNA polymerase
2. Taq polymerase
3. Alkaline phosphatase
4. DNA ligase

Answer. 4. DNA ligase

Question 9. Which is incorrect with respect to DNA polymerase III?

1. It requires ATP for polymerase action.
2. It is required for PCR.
3. It is more active than DNA polymerases I and II.
4. It requires a pre-formed DNA template to work on.

Answer. 2. It is required for PCR.

Question 10. Which is not an application of modern biotechnology?

1. Production of humulin
2. Developing a DNA vaccine
3. Gene therapy
4. Production of cheese and butter

Answer. 4. Production of cheese and butter

Question 11. Which of the following cannot be related to biotechnology?

1. Integration of natural science and organisms.
2. Techniques to alter the chemistry of DNA.
3. Introducing undesirable genes into the target organism.
4. Maintenance of sterile ambience to enable the growth of only the desired microbes.

Answer. 3. Introducing undesirable genes into the target organism.

Question 12. Which of the following specific DNA sequence is responsible for initiating replication?

1. Vector site
2. Restriction enzymes action site
3. Ori site
4. Palindromic site

Answer. 3. Ori site

Question 13. Autonomously replicating, circular, extra chromosomal DNA of prokaryotic cell is called

1. Satellite DNA
2. Plasmid
3. Recombinant DNA
4. Nucleoid

Answer. 2. Plasmid

Question 14. Key tools to be involved in recombinant DNA technology are

A. Restriction enzymes

B. Polymerase enzyme

C. Ligase enzymes

D. Vectors

1. (A) only
2. (A) and (C) only
3. (A), (B), and (C)
4. (A), (B), (C), and (D)

Answer. 4. (A), (B), (C), and (D)

Question 15. The first restriction endonuclease to be discovered was

1. Hind II
2. Eco RI
3. Bam HI
4. Pst I

Answer. 1. Hind II

Question 16. Approximately, how many restriction enzymes have been isolated from the different (over 230) strains of bacteria?

1. 300
2. 600
3. 750
4. 900

Answer. 4. 900

Question 17. The conventional method for naming restriction enzymes is followed. In case of Eco RI, the “R” indicates

1. Genus
2. Species
3. Name of the scientist
4. Strain

Answer. 4. Strain

Question 18. The restriction endonuclease enzyme binds to the DNA and cuts

1. Any one strand of the double helix
2. Each of the two strands at specific points in their base-sugar bonds
3. Each of the two strands at specific points in their base-phosphate bonds
4. Each of the two strands at specific points in their sugar-phosphate backbones

Answer. 4. Each of the two strands at specific points in their sugar-phosphate backbones

Question 19. During gel electrophoresis, for the separation of DNA fragment, the

1. Smallest fragment will move to the farthest point towards cathode
2. Smallest fragment will move to the farthest point towards anode
3. Largest fragment will move to the farthest point towards cathode
4. Largest fragment will move to the farthest point towards anode

Answer. 2. Smallest fragment will move to the farthest point towards anode

Question 20. After electrophoresis, the separated DNA fragment can be visualized in ethidium bromide gel exposed to UV light. These DNA fragments appear as _________ colored bands.

1. Orange
2. Blue
3. Silver
4. Green

Answer. 1. Orange

Question 21. The procedure through which a piece of DNA is introduced in a host bacterium is called

1. Cloning
2. Transformation
3. PCR
4. Clonal selection

Answer. 2. Transformation

Question 22. After completing the transformation experiment involving the coding sequence of enzyme a-galactosidase, the recombinant colonies should

1. Give blue color
2. Not give blue color
3. Have active α-galactosidase
4. Both (2) and (3)

Answer. 2. Not give blue color

Question 23. Which of the following has the ability to transform normal cells into cancerous cells in animals?

1. Agrobacterium tumifaciens
2. Retroviruses
3. DNA viruses
4. Plasmids

Answer. 2. Retroviruses

Question 24. Which of the following is not applicable to Agrobacterium tumifaciens?

1. Pathogen of several dicot plants.
2. Has the ability to transform normal plant cells.
3. Delivers gene of our interest.
4. Ti plasmid of it is always pathogenic to plants with out any exception.

Answer. 4. Ti plasmid of it is always pathogenic to plants with out any exception.

Question 25. Insertional inactivation is related to

1. Microinjection
2. Gene gun
3. Gel electrophoresis
4. Selection of recombinants

Answer. 4. Selection of recombinants

Question 26. For transformation with recombinant DNA, the bacterial cells must first be made competent, which means

1. Should increase their metabolic reactions
2. Should decrease their metabolic reactions
3. Increase efficiency with which DNA enters the bacterium
4. Ability to divide fast

Answer. 3. Increase efficiency with which DNA enters the bacterium

Question 27. Which of the following method can be used for making the bacterial cell competent?

1. Treating with specific concentration of divalent cation (Ca2+).
2. Treating with specific concentration of monovalent cation (K).
3. Heat shock.
4. Both (1) and (3).

Answer. 4. Both (1) and (3).

Question 28. Which of the following techniques can be used to introduce foreign DNA into cell?

1. Using disarmed pathogen
2. Microinjection
3. Gene gun
4. All of these

Answer. 4. All of these

Question 29. During heat shock, the temperature used for giving thermal shock to the bacterium is

1. 82°C
2. 100°C
3. Liquid nitrogen
4. 42°C

Answer. 4. 42°C

Question 30. Which of the following enzymes is used in case of fungus to cause the release of DNA along with other macromolecules?

1. Lysozyme
2. Cellulase
3. Chitinase
4. Amylase

Answer. 3. Chitinase

Question 31. During the isolation of DNA, the addition of which of the following causes the precipitation of purified DNA?

1. Chilled ethanol
2. Ribonuclease enzyme
3. DNA polymerase
4. Proteases

Answer. 1. Chilled ethanol

Question 32. Which of the following is the correct sequence of PCR (polymerase chain reaction)?

1. Denaturation → Annealing → Extension
2. Extension → Denaturation → Annealing
3. Annealing → Extension → Denaturation
4. Denaturation → Extension → Annealing

Answer. 1. Denaturation → Annealing → Extension

Question 33. The most commonly used bioreactor is of stirring type. The stirrer facilitates

1. Temperature control
2. pH control
3. Oxygen availability
4. Product removal

Answer. 3. Oxygen availability

Question 34. After the completion of biosynthetic stage, the separation and purification of product is called

1. Upstream processing
2. Downstream processing
3. Modern biotechnology
4. Gene amplification

Answer. 2. Downstream processing

Question 35. From isolated DNA from a cell culture with seven de- sired genes, DNA segment can be excised by molecular scissors or chemical scalpels what biotechnologists call as

1. Polymerase enzymes
2. DNA ligase
3. Restriction enzymes
4. Helicase

Answer. 3. Restriction enzymes

Question 36. All the following statements about Stanley Cohen and Herbert Boyer are correct but one is wrong. Which one is wrong?

1. They discovered recombinant DNA (rDNA) technology, and this marks the birth of modern biotechnology.
2. They first produced healthy sheep clone, a Finn Dorset lamb, Dolly, from the differentiated adult mammary cells.
3. They invented genetic engineering by combining a piece of foreign DNA containing a gene from a bacterium with a bacterial plasmid using the enzyme restriction endonuclease.
4. They isolated the antibiotic resistance gene by cutting out a piece of DNA from the plasmid which was responsible for conferring antibiotic resistance.

Answer. 2. They first produced healthy sheep clone, a Finn Dorset lamb, Dolly, from the differentiated adult mammary cells.

Question 37. What is the fate of a piece of DNA which is somehow transferred into an alien organism?

1. This piece of DNA would not be able to multiply itself in the progeny cells of the organism if not integrated into the genome of the organism.
2. If the alien piece of DNA has become a part of the chromosome, it will replicate.
3. If the alien piece of DNA is linked with the origin of replication in chromosome, it will replicate.
4. All of these.

Answer. 4. All of these.

Question 38. In the year 1963, the two enzymes responsible for restricting the growth of bacteriophage in Escherichia coli were isolated. These were and, respectively.

1. Ligase, restriction endonuclease
2. Helicase, restriction endonuclease
3. Methylase, restriction endonuclease
4. DNA polymerase, restriction endonuclease

Answer. 3. Methylase, restriction endonuclease

Question 39. The cutting of DNA by restriction endonucleases results in fragments of DNA. These fragments are generally separated by a technique known as

1. Gel-filtration chromatography
2. Centrifugation
3. Gel electrophoresis
4. Thin-layer chromatography

Answer. 3. Gel electrophoresis

Question 40. Which of the following bacteria are known as natural genetic engineers of plants, as gene transfer is happening in nature without human interference?

1. Azotobacter
2. Agrobacterium tumefaciens
3. Escherichia coli
4. Rhizobium

Answer. 2. Agrobacterium tumefaciens

Question 41. The technique in which a foreign DNA is precipitated on the surface of tungsten or gold particles and shot into the target cells is known as

1. Microinjection
2. Chemical-mediated genetic transformation
3. Electroporation
4. Biolistics

Answer. 4. Biolistics

Question 42. The isolation of the genetic material in pure form-free from other macromolecules can be achieved by treating the bacterial cells/plant or animal tissues with the following enzymes, except

1. Lysozyme
2. Cellulase
3. Chitinase
4. Ligase

Answer. 4. Ligase

Question 43. Which of the following is not a recombinant protein used in medical practice?

1. TPA (tissue plasminogen activator)
2. Interferon (α, B, and 7)
3. Vaccine (for hepatitis B)
4. Heparin

Answer. 4. Heparin

Question 44. cDNA is

1. Circular DNA in bacteria
2. Complementary DNA
3. Copy DNA
4. Both (2) and (3)

Answer. 4. Both (2) and (3)

Question 45. The Noble Prize of 1978 for restriction endonuclease technology was given to

1. Temin and Baltimore
2. Milstein and Kohler
3. Arber, Nathans, and Smith
4. Holley, Khorana, and Nirenberg

Answer. 3. Arber, Nathans, and Smith

Question 46. Plasmids are used in genetic engineering because they

1. Are easily available
2. Are able to integrate with host chromosome
3. Are able to replicate along with chromosomal DNA
4. Contain DNA sequence coding for drug resistance

Answer. 3. Are able to replicate along with chromosomal DNA

Question 47. Which of the following processes and techniques are included under biotechnology?

A. In vitro fertilization leading to a test-tube baby.

B. Synthesizing gene and using it.

C. Developing DNA vaccine.

D. Correcting a defective gene.

1. (B) and (D) only (3)
2. (B), (C), and (D)
3. (A) and (B)
4. (A), (B), (C), and (D)

Answer. 4. (A), (B), (C), and (D)

Question 48. The tumor-inducing (Ti) plasmid has now been modified to a cloning vector which is no more pathogenic to plants but is still able to use mechanisms to deliver genes of our interest into a variety of plants because Ti plasmid has been modified by

1. Adding tumor-forming genes
2. Deleting tumor-forming genes
3. Adding genes resistant to endonucleases
4. Deleting endonuclease

Answer. 2. Deleting tumor-forming genes

Question 49. Which of the following statements is incorrect?

1. Plasmids have the ability to replicate within the bacterial cells independent of the control of chromosomal DNA.
2. Some plasmids have only one or two copies per cell whereas others may have 15-100 copies per cell.
3. Bacteriophages have the ability to replicate within the bacterial cell independent of the control of chromosomal DNA.
4. Transformation is a procedure of separation and isolation of DNA fragments.

Answer. 4. Transformation is a procedure of separation and isolation of DNA fragments.

Question 50. Which of the following is the first artificial cloning vector that has two selectable markers-tetracycline (tetR) and antibiotic restriction enzymes (ampR)?

1. YAC
2. BAC
3. pBR322
4. Cosmid vectors

Answer. 3. pBR322

Question 51. Restriction endonucleases are most widely used in recombinant DNA technology. They are obtained from

1. Bacteriophage
2. Bacterial cells
3. Plasmids
4. All prokaryotic cells

Answer. 2. Bacterial cells

Question 52. All the following statements are correct about genetic engineering, but one is wrong. Which one is wrong?

1. It is a technique for artificially and deliberately modifying DNA (genes) to suit human needs.
2. It is often referred as gene splicing.
3. The organism carrying the foreign genes is termed as transgenic or GMO.
4. Alec Jeffrey is the father of genetic engineering.

Answer. 4. Alec Jeffrey is the father of genetic engineering.

Question 53. All the following are the properties of enzyme Taq polymerase, except

1. It is thermostable DNA polymerase
2. It is isolated from a bacterium, Thermus aquaticus
3. It is used for the amplification of gene of interest using PCR
4. It is thermostable RNA polymerase

Answer. 4. It is thermostable RNA polymerase

Question 54. Which of the following is incorrect match?

1. Gene therapy: An abnormal gene is replaced by normal gene
2. Cloning: Ability to multiply copies of antibiotic resistance gene in E. coli
3. Restriction enzymes: Molecular scissors
4. Exonucleases: Molecular glue

Answer. 4. Exonucleases: Molecular glue

Question 55. Appropriate techniques have been developed for large- scale cell culture using bioreactors for producing

1. Foreign gene product
2. Vaccines
3. Hormones
4. All of these

Answer. 4. All of these

Question 56. The uptake of genes by cells in microbes and plants is termed as

1. Insertional inactivation
2. Transformation
3. Selectable markers
4. Cloning vectors

Answer. 2. Transformation

Question 57. If we ligate a foreign DNA at the BamHI site of tetracycline resistance gene in pBR322, the recombinant plasmid will

1. Show ampicillin resistance only
2. Show tetracycline resistance
3. Will grow well on tetracycline-containing medium
4. Will not grow on ampicillin-containing medium

Answer. 1. Show ampicillin resistance only

Question 58. Polyethylene glycol can help in the uptake of foreign DNA into the host cell. This type of gene transfer is called

1. Electroporation
2. Chemical mediated genetic transformation
3. Microinjection
4. Particle gun

Answer. 2. Chemical mediated genetic transformation

Question 59. The normal E. coli cells carry resistance against which of the following antibiotics?

1. Ampicillin
2. Chloramphenicol
3. Tetracycline or kanamycin
4. None of these

Answer. 4. None of these

Question 60. The isolation of genetic material from fungal cells does not involve the use of

1. Agarose
2. Chitinase
3. Ethanol
4. Water

Answer. 1. Agarose

Question 61. In a restriction digestion experiment, the sticky ends of vector rejoined forming a circular vector without insert. Which enzyme can be used to eliminate this possibility?

1. DNA ligase
2. Alkaline phosphatase
3. DNA polymerase
4. RNA polymerase

Answer. 2. Alkaline phosphatase

Question 62. Denaturation can be achieved at which temperature during PCR?

1. 72°C
2. 95°C
3. 40°C
4. 25°C

Answer. 2. 95°C

Question 63. Choose the incorrect statement with respect to Agrobacterium tumefaciens.

1. It is a Gram-negative soil bacterium.
2. It produces crown gall disease in dicot plants.
3. The foreign DNA is inserted at the ori site of Ti plasmid.
4. Ti plasmid becomes incorporated into the plant chromosomal DNA.

Answer. 3. The foreign DNA is inserted at the ori site of Ti plasmid.

Question 64. Which is not a method for the introduction of recombinant DNA into host cells?

1. Electroporation
2. Biolistics
3. Transfection
4. Restriction digestion

Answer. 4. Restriction digestion

Question 65. The essential requirements for a gene amplification reaction are

1. 20 mg of DNA template
2. Forward and reverse primers
3. Mg2+
4. All of these

Answer. 4. All of these

Question 66. Choose the incorrect statement with respect to PCR reaction:

1. It requires Taq polymerase.
2. It requires dNTP’s.
3. It generates 2n molecules after n number of cycles.
4. The optimum temperature for polymerization step is greater than or equal to 90°C.

Answer. 4. The optimum temperature for polymerization step is greater than or equal to 90°C.

Question 67. Which is not an application of PCR?

1. DNA fingerprinting
2. DNA foot-printing
3. Detection of mutation
4. Prenatal diagnosis

Answer. 2. DNA foot-printing

Question 68. Rejoining of vector molecule after restriction enzyme digestion can be avoided by

1. Using different enzymes for insert and vector
2. Using same enzyme for insert and vector
3. Using DNA ligase immediately after digestion
4. Using alkaline phosphatase on only vector

Answer. 4. Using alkaline phosphatase on only vector

Question 69. If the target gene is inserted at Sal 1 site of the recombinant, plasmid will show resistance for pBR322

1. Ampicillin
2. Tetracyline
3. Both (1) and (2)
4. Kanamycin

Answer. 1. Ampicillin

Question 70. It is theoretically possible for a gene from any organism to function in any other organism. Why is this possible?

1. All organisms have ribosomes.
2. All organisms have the same genetic code.
3. All organisms are made up of cells.
4. All organisms have similar nuclei.

Answer. 2. All organisms have the same genetic code.

Question 71. If you discovered a bacterial cell that contained no restriction enzymes, which of the following would you except to happen?

1. The cell would create incomplete plasmids.
2. The cell would be unable to replicate its DNA.
3. The cell would become an obligate parasite.
4. The cell would be easily infected by bacteriophages.

Answer. 4. The cell would be easily infected by bacteriophages.

Question 72. Assume that you are trying to insert a gene into a plasmid and someone gives you a preparation of DNA cut with restriction enzyme X. The gene you wish to insert has sites on both ends for cutting by restriction enzyme Y. You have a plasmid with a single site for Y, but not for X. Your strategy should be to

1. Cut the plasmid with restriction enzyme X and insert the fragments cut with Y into the plasmid
2. Cut the plasmid with restriction enzyme X and insert the gene into the plasmid
3. Cut the plasmid twice with restriction enzyme Y and ligate the two fragments into the plasmid cut with the same enzyme
4. Cut the plasmid twice with restriction enzyme Y and ligate the two fragments onto the ends of the human DNA fragments cut with restriction enzyme X

Answer. 3. Cut the plasmid twice with restriction enzyme Y and ligate the two fragments into the plasmid cut with the same enzyme

Question 73. 1. Transform bacteria with recombinant DNA molecule.

2. Cut the plasmid DNA using restriction enzymes.

3. Extract plasmid DNA from bacterial cells.

4. Hydrogen-bond the plasmid DNA to non-plasmid DNA fragments.

5. Use ligase to seal plasmid DNA to non-plasmid DNA.

From the given list, which of the following is the most logical sequence of steps for splicing foreign DNA into a plasmid and inserting the plasmid into a bacterium?

1. 4, 5, 1, 2, 3
2. 3, 2, 4, 5, 1
3. 3, 4, 5, 1, 2
4. 2, 3, 5, 4, 1

Answer. 2. 3, 2, 4, 5, 1

Question 74. A eukaryotic gene has sticky ends produced by restriction endonuclease Eco RI. The gene is added to a mixture containing Eco RI and a bacterial plasmid that carries two genes, which make it resistant to ampicillin and tetracyline. The plasmid has one recognition site for Eco RI located in the tetracycline resistance gene. This mixture is incubated for several hours and then added to bacteria growing in nutrient broth. The bacteria are allowed to grow overnight and are streaked on a plate using a technique which produces isolated colonies that are clones of the original. Samples of these colonies are then grown in four different media: nutrient broth plus ampicillin, nutrient broth plus tetracycline, nutrient broth plus ampicillin and tetracycline, and nutrient broth containing no antibiotics.

The bacteria containing the engineered plasmid would grow in

1. The ampicillin and tetracycline broth only
2. The nutrient broth, the ampicillin broth, and the tetracycline broth
3. The nutrient broth and the ampicillin broth only
4. The nutrient broth only

Answer. 3. The nutrient broth and the ampicillin broth only

Question 75. Agrobacterium tumefaciens is used in genetic engineering for

1. DNA mapping
2. DNA modification
3. Vector
4. DNA fingerprinting

Answer. 3. Vector

Question 76. A genetically engineered bacteria used for clearing oil spills is

1. Escherischia coli
2. Bacillus subtilis
3. Agrobacterium tumefaciens
4. Pseudomonas putida

Answer. 4. Pseudomonas putida

Question 77. Who isolated the first restriction endonucleases?

1. Temin and Baltimore
2. Sanger
3. Nathans and Smith
4. Paul Berg

Answer. 3. Nathans and Smith

Question 78. Genetic engineering is

1. Study of extra-nuclear gene
2. Manipulation of genes by artificial method
3. Manipulation of RNA
4. Manipulation of enzymes

Answer. 2. Manipulation of genes by artificial method

Question 79. Which of the following enzymes cut the DNA molecule at specific nucleotide sequence?

1. Restriction endonuclease
2. DNA ligase
3. RNA polymerase
4. Exonuclease

Answer. 1. Restriction endonuclease

Question 80. DNA fingerprinting was invented by

1. Karl Mullis
2. Alec Jeffery
3. Dr. Paul Berg
4. Francis Collins

Answer. 2. Alec Jeffery

Question 81. Which structure is involved in genetic engineering?

1. Plastid
2. Plasmid
3. Codon
4. None

Answer. 2. Plasmid

Question 82. Which of the following is the example of chemical scissors?

1. Eco RI
2. HindIII
3. Bam I
4. All of the above

Answer. 4. All of the above

Question 83. Restriction endonucleases are used in genetic engineering because

1. They can degrade harmful proteins
2. They can join DNA fragments
3. They can cut DNA at variable sites
4. They can cut DNA at specific base sequences

Answer. 4. They can cut DNA at specific base sequences

Question 84. Chimeric DNA is

1. DNA which contains uracil
2. DNA synthesized from RNA
3. Recombinant DNA
4. DNA which contains single strand

Answer. 3. Recombinant DNA

Question 85. A piece of nucleic acid used to find out a gene by forming hybrid with it is called

1. cDNA
2. DNA probe
3. Sticky end
4. Blunt end

Answer. 2. DNA probe

Question 86. Which of the following is the example of direct gene transfer?

1. Microinjection
2. Electroporation
3. Particle gun
4. All the above

Answer. 4. All the above

Question 87. How many copies of DNA sample are produced in PCR technique after 6 cycles?

1. 4
2. 32
3. 16
4. 64

Answer. 3. 16

Question 88. The basic procedure involved in the synthesis of recombinant DNA molecule is depicted. The mistake in the cedure is procedure is

1. Enzyme polymerase is not included
2. The mammalian DNA is shown double stranded
3. Only one fragment is inserted
4. Two different restriction enzymes are used

Answer. 4. Two different restriction enzymes are used

Question 89. Western blotting is used for the identification of

1. DNA
2. RNA
3. Protein
4. All the above

Answer. 3. Protein

Question 90. In rDNA technique, which of the following technique is not used in introducing DNA into host cell?

1. Transduction
2. Conjugation
3. Transformation
4. Electroporation

Answer. 2. Conjugation

Question 91. Which of the following techniques are used in analyzing restriction fragment length polymorphism (RFLP)?

(a) Electrophoresis

(b) Electroporation

(c) Methylation

(d) Restriction digestion

1. (a) and (c)
2. (c) and (d)
3. (a) and (d)
4. (b) and (d)

Answer. 3. (a) and (d)

Question 92. Restriction enzymes are

1. Not always required in genetic engineering
2. Essential tool in genetic engineering
3. Nucleases that cleave DNA at specific sites
4. (2) and (3) both

Answer. 4. (2) and (3) both

Question 93. The function of restriction endonuclease enzyme is

1. It is useful in genetic engineering
2. It protects the bacterial DNA against foreign DNA
3. It is helpful in transcription
4. It is helpful in protein synthesis

Answer. 2. It protects the bacterial DNA against foreign DNA

Question 94. A bacterium modifies its DNA by adding methyl groups to the DNA. It does so to

1. Clone its DNA
2. Be able to transcribe many genes simultaneously
3. Turn its gene on
4. Protect its DNA from its own restriction enzyme

Answer. 4. Protect its DNA from its own restriction enzyme

Question 95. Plasmid has been used as vector because

1. It is circular DNA which has capacity to join eukaryotic DNA
2. It can move between prokaryotic and eukaryotic cells
3. Both ends show replication
4. It has antibiotic resistance gene

Answer. 1. It is circular DNA which has capacity to join eukaryotic DNA

Question 96. Which of the following cuts the DNA from specific places?

1. Restriction endonuclease (Eco RI)
2. Ligase
3. Exonuclease
4. Alkaline phosphate

Answer. 1. Restriction endonuclease (Eco RI)

Question 97. The manipulation of DNA in genetic engineering becomes possible due to the discovery of

1. Restriction endonuclease
2. DNA ligase
3. Transcriptase
4. Primase

Answer. 1. Restriction endonuclease

Question 98. Restriction enzymes

1. Are endonucleases which cleave DNA at specific sites
2. Make DNA complementary to an existing DNA or RNA
3. Cut or join DNA fragments
4. Are required in vector-less direct gene transfer

Answer. 1. Are endonucleases which cleave DNA at specific sites

Question 99. DNA fingerprinting refers to

1. Techniques used for the identification of fingerprints of individuals
2. Molecular analysis of profiles of DNA samples
3. Analysis of DNA samples using imprinting devices
4. Techniques used for molecular analysis of different specimens of DNA

Answer. 2. Molecular analysis of profiles of DNA samples

Question 100. Restriction endonucleases

1. Are synthesized by bacteria as part of their defense compound
2. Are present in mammalian cells for degradation of DNA when the cell dies
3. Are used in genetic engineering for ligating two DNA molecules
4. Are used for in vitro DNA synthesis

Answer. 1. Are synthesized by bacteria as part of their defense compound

Question 101. What is the first step in the Southern blot technique?

1. Denaturation of DNA on the gel for hybridization with specific probe.
2. Production of a group of genetically identical cells.
3. Digestion of DNA by restriction enzyme.
4. Isolation of DNA from a nucleated cell such as the one from the scene of crime.

Answer. 1. Denaturation of DNA on the gel for hybridization with specific probe.

Question 102. Which of the following is not produced by E. coli in lactose?

1. B-galactosidase
2. Thiogalactoside transacetylase
3. Lactose dehydrogenase
4. Lactose permease

Answer. 3. Lactose dehydrogenase

Question 103. The technique of transferring DNA fragment separated on agarose gel to a synthetic membrane such as nitrocellulose is known as

1. Northern blotting
2. Southern blotting
3. Western blotting
4. Dot blotting

Answer. 2. Southern blotting

Question 104. The production of a human protein in bacteria in genetic engineering is possible because

1. Bacterial cell can carry out RNA splicing reactions
2. The mechanism of gene regulation is identical in humans and bacteria
3. Human chromosome can replicate in bacterial cell
4. Genetic code is universal

Answer. 4. Genetic code is universal

Question 105. Electroporation procedure involves

1. Fast passage of food through sieve pores in phloem elements with the help of electric stimulation
2. Opening of stomatal pores during night by artificial light
3. Making transient pores in the cell membrane to introduce gene constructs
4. Purification of saline water with the help of a membrane system

Answer. 3. Making transient pores in the cell membrane to introduce gene constructs

Question 106. The total number of nitrogenous bases in human genome is estimated to be about

1. 3.5 million
2. 35 thousand
3. 35 million
4. 3.1 billion

Answer. 4. 3.1 billion

Question 107. Two microbes found to be very useful in genetic engineering are

1. Escherichia coli and Agrobacterium tumefaciens
2. Vibro cholerae and a tailed bacteriophage
3. Diplococcus sp. and Pseudomonas sp.
4. Crown gall bacterium and Caenorhabdits elegans

Answer. 1. Escherichia coli and Agrobacterium tumefaciens

Question 108. Restriction endonuclease

1. Cuts the DNA molecule randomly
2. Cuts the DNA molecule at specific sites
3. Restricts the synthesis of DNA inside the nucleus
4. Synthesizes DNA

Answer. 2. Cuts the DNA molecule at specific sites

Question 109. The restriction enzyme Eco RI has the property of

1. Endonuclease activity
2. Exonuclease activity
3. Ligation activity
4. Correcting the topology of replicating DNA

Answer. 1. Endonuclease activity

Question 110. DNA ligase is an enzyme that catalyzes the

1. Splitting of DNA threads into small bits
2. Joining of the fragments of DNA
3. Denaturation of DNA
4. Synthesis of DNA

Answer. 2. Joining of the fragments of DNA

Question 111. More advancement in genetic engineering is due to

1. Restriction endonuclease
2. Reverse transcriptase
3. Protease
4. Zymase

Answer. 1. Restriction endonuclease

Question 112. The function of PCR is

1. Translation
2. Transcription
3. DNA amplification
4. None of these

Answer. 3. DNA amplification

Question 113. Which of the following is used as the best genetic vector?

1. Bacillus thuriengenesis
2. Agrobacterium tumefaciens
3. Pseudomonas putida
4. All of these

Answer. 2. Agrobacterium tumefaciens

Question 114. The transfer of protein from electrophoretic gel to nitrocellulose membrane is known as

1. Transferase
2. Northern blotting
3. Western blotting
4. Southern blotting

Answer. 3. Western blotting

Question 115. DNA fingerprinting was first discovered by

1. Alec Jeffery
2. Cark Mullis
3. C. Milstein
4. Dr. Paul Berg

Answer. 1. Alec Jeffery

Question 116. Which of the following enzyme is used to join DNA fragments?

1. Terminase
2. Endonuclease
3. Ligase
4. DNA polymerase

Answer. 3. Ligase

Question 117. Restriction endonucleases are enzymes which

1. Make cuts at specific positions within the DNA molecule
2. Recognize a specific nucleotide sequence for binding of DNA ligase
3. Restrict the action of enzyme DNA polymerase
4. Remove nucleotides from the ends of the DNA molecule

Answer. 1. Make cuts at specific positions within the DNA molecule

Question 118. Satellite DNA is a useful tool in

1. Organ transplantation
2. Sex determination
3. Forensic science
4. Genetic engineering

Answer. 3. Forensic science

Question 119. PCR and restriction fragment length polymorphism are the methods for

1. Genetic transformation
2. DNA sequencing
3. Genetic fingerprinting
4. Study of enzymes

Answer. 3. Genetic fingerprinting

Question 120. Which one is a true statement regarding DNA polymerase used in PCR?

1. It serves as a selectable marker.
2. It is isolated from a virus.
3. It remains active at high temperature.
4. It is used to ligate introduced DNA in recipient cells.

Answer. 3. It remains active at high temperature.

Question 121. For transformation, microparticles coated with DNA to be bombarded with gene gun are made up of

1. Platinum or zinc
2. Silicon or platinum
3. Gold or tungsten
4. Silver or platinum

Answer. 3. Gold or tungsten

Question 122. A single strand of nucleic acid tagged with a radioactive molecule is called

1. Selectable marker
2. Plasmid
3. Probe
4. Vector

Answer. 3. Probe

Question 123. The following figure is the diagrammatic representation of the E. coli vector PBR 322. Which one of the given options correctly identifies its certain component(s)? 

1. rop-reduced osmotic pressure
2. Hind III, Eco RI-selectable markers
3. ampR, tetR-antibiotic resistance genes
4. ori-original restriction enzyme

Answer. 3. ampR, tetR-antibiotic resistance genes

Question 124. Which one of the following is a case of wrong matching?

1. Vector DNA: Site for tRNA synthesis
2. Micropropagation: In vitro production of plants in large numbers
3. Callus: Unorganized mass of cells produced in tissue culture
4. Somatic hybridization: Fusion of two diverse cells

Answer. 1. Vector DNA: Site for tRNA synthesis

Question 125. Biolistics (gene gun) is suitable for

1. Disarming pathogen vectors
2. Transformation of plant cells
3. Constructing recombinant DNA by joining with vectors
4. DNA fingerprinting

Answer. 3. Constructing recombinant DNA by joining with vectors

Question 126. In genetic engineering, the antibiotics are used

1. As selectable markers
2. To select healthy vectors
3. As sequences from where replication starts
4. To keep the cultures free of infection

Answer. 1. As selectable markers

Question 127. What is it that forms the basis of DNA fingerprinting?

1. The relative proportions of purines and pyrimidines in DNA.
2. The relative difference in the DNA occurrence in blood, skin, and saliva.
3. The relative amount of DNA in the ridges and grooves of fingerprints.
4. Satellite DNA occurring as highly repeated short DNA segments.

Answer. 4. Satellite DNA occurring as highly repeated short DNA segments.

Question 128. The following figure shows three steps (A)-(C) of PCR. Select the option giving correct identification together with what it represents?

Options:

1. B-Denaturation at a temperature of about 98°C separating the two DNA strands
2. A-Denaturation at a temperature of about 50°C
3. C-Extension in the presence of heat stable DNA polymerase
4. A-Annealing with two sets of primers

Answer. 3. C-Extension in the presence of heat stable DNA polymerase

Question 129. Which one of the following represents a palindromic sequence in DNA?

1. 5′-GAATTC-3′; 3′- CTTAAG-5′
2. 5′-CCATCC-3′; 3′-GAATCC-5′
3. 5′-CATTAG-3′; 3′-GATAAC-5′
4. 5′-GATACC-3′; 3′-CCTAAG-5′

Answer. 1. 5′-GAATTC-3′; 3′- CTTAAG-5′

Question 130. DNA fragments generated by restriction endonucleases in a chemical reaction can be separated by

1. Polymerase chain reaction
2. Electrophoresis
3. Restriction mapping
4. Centrifugation

Answer. 2. Electrophoresis

Question 131. The colonies of recombinant bacteria appear white in contrast to the blue colonies of non-recombinant bacteria because of

1. Insertional inactivation of alpha-galactosidase in non-recombinant bacteria
2. Insertional inactivation of alpha-galactosidase in recombinant bacteria
3. Inactivation of glycosidase enzyme in recombinant bacteria
4. Non-recombinant bacteria containing beta-galactosidase

Answer. 4. Non-recombinant bacteria containing beta-galactosidase

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: DNA ligase plays important role in recombinant DNA technology.

Reason: The linking of antibiotic resistance gene with plasmid vector became possible by enzyme DNA ligase.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark(1).

Question 2. Assertion: Restriction enzymes belong to a larger class of enzymes called nucleases.

Reason: Each restriction enzyme recognizes a specific palindromic nucleotide sequence in the DNA.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 3. Assertion: During gel electrophoresis, DNA fragments move towards the anode.

Reason: DNA fragments are negatively charged molecules.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark(1).

Question 4. Assertion: The selection of recombinants due to inacti- vation of antibiotics is a cumbersome procedure.

Reason: It requires simultaneous plating on two plates having different antibiotics.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark(1).

Question 5. Assertion: Taq polymerase is involved in PCR technique.

Reason: This enzyme remains active during high temperature including denaturation of double-stranded DNA.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark(1).

Question 6. Assertion: Small DNA fragments will arrange towards the positive end after gel electrophoresis in DNA test.

Reason: DNA is negatively charged.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark(1).

Question 7. Assertion: PCR technique is used in the amplification of a specific gene.

Reason: In PCR technique, Taq polymerase enzyme is used, and this enzyme is thermosensitive.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Microbes In Human Welfare

Microbes In Household Products

Dairy Products

• Lactic acid bacteria (LAB) such as Lactobacillus are added to milk. Lactobacillus converts the lactose sugar of milk into lactic acid.
• Milk can be changed into curd, yoghurt, and cheese. The starter used in the preparation of milk products actually contains millions of LAB.
  • Curd: Indian curd is prepared by inoculating cream and skimmed milk with Lactobacillus acidophilus at a temperature of about 40°C or less. Curd is more nutritious than milk as it contains a number of vitamins, especially Vitamin B12 and organic acids.
  • Yoghurt: It is produced by curdling milk with the help of Streptococcus thermophilus and Lactobacillus bulgaricus. It has the flavor of lactic acid and acetaldehyde.
  • Butter milk: It is an acidulated product which is formed by inoculating skimmed milk with the starter culture of Streptococcus cremoris, S. lactis, Lactobacillus acidophilus, and Leuconostoc species at 22°C for 18 h.
  • Sour cream: It is inoculated with Streptococcus lactis for producing lactic acid and with Leuconostoc cremoris for imparting the characteristic flavor.
  • Cheese: It is a partially degraded concentrate of milk fat and casein manufactured by the activity of microorganisms. There are several hundred varieties of cheese which are prepared by selected types of microorganisms. The quality and characteristic taste of cheese are is determined by the biochemical activities of specific microorganisms. Cheese consists of milk curd that has separated from whey or liquid part. Cheese is of three types: (i) soft (50-80% water), (ii) semi-hard (about 45% water), and (iii) hard (less than 40% water). The method of preparing cheese with the help of microbes was known in Asia and Europe long before Christ. Large-holed Swiss cheese is ripened with the help of CO, producing bacterium called Propionibacterium sharmanii; Roquefort cheese or blue cheese uses Penicillium roquefortii: Camembert cheese employs Penicillium camembertii for ripening.

Bread

• Selected strains of Saccharomyces cerevisiae (baker’s yeast) grown on molasses are used for this purpose.
• The kneaded flour is kept at a warm temperature for a few hours. It swells up. The phenomenon is called leavening.
• Leavening is caused by the secretion of three types of enzymes by yeast. They are amylase, maltase, and zymase.
• The leavened dough is baked. Both carbon dioxide and ethyl alcohol evaporate, making the bread porous and soft.

Dosa, Uppma, and Idli

Dosa, uppma, and idli are fermented preparations of rice and black gram. The two are allowed to ferment for 3-12 h with Leuconostoc and Streptococcus species of bacteria.

• Other Foods Tempeh (Indonesia), tofu (Japanese), and sufu (Chinese) are fermented foods obtained from soya saucebrown flavored salty sauce fermented from soybean and wheat.
• Tender bamboo shoots can be used as vegetable directly as well as after fermentation. Several types of sausages are prepared by fermentation and curing of fish and meat.

Read and Learn More NEET Biology Notes

Toddy (Toddy palm or Caryota urens)

The unopened spadices of palm are tapped to obtain toddy. It is a refreshing drink which can be heated to produce jaggery or palm sugar. Toddy left for a few hours undergoes fermentation with the help of naturally occurring yeast to form beverage containing about 6% alcohol.

Microbes In Industrial Products

Fermentative activity of microbes is used industrially to obtain a number of products. Production on an industrial scale requires growing microbes in very large vessels called fermentors. The two common ones are alcoholic fermentation and antibiotics.

Fermented Beverages/Alcoholic Fermentation

• Yeast species used in alcoholic fermentation are Saccharomyces cerevisiae (brewer’s yeast), S. ellipsoidens (wine yeast), S. sake (sake yeast), and S. pireformis (ginger beer/ale yeast).
• The nutrient media are barley malt for beer, fermented rye malt for gin, fermented rice for sake, cashew-apple for fenny, potato for vodka, fermented cereals for whisky, fermented molasses for rum, and fermented juices for wines and brandy.
• Wine and beer are produced without distillation, whereas whisky (50% alcohol), brandy (65-70% alcohol), rum (40% alcohol), and gin (about 40% al- cohol) are produced by the distillation of fermented broth.

Antibiotics

• An antibiotic (Greek: against life) is a substance produced by a microorganism which in low concentration inhibits the growth and metabolic activity of pathogenic organisms without harming the host.
• This is among the most significant discoveries of the 20th century.
• The first antibiotic is generally associated with the name of Alexander Fleming (1928), when he discovered penicillin from Penicillium notatum.
• The antibiotic was, however, commercially extracted by the efforts of Ernst Chain and Howard Florey. The chemical was extensively used in treating wounded American soldiers in World War II. Fleming, Chain, and Florey were awarded Nobel Prize in 1945. A bulk of antibiotics is obtained from three groups of micro- organisms: Eubacteria, actinomycetes, and fungi.
• Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough, diphtheria, and leprosy. So, with reference to human beings, these are pro-life.

Chemicals, Enzymes, and Other Bioactive Molecules

Bioactive molecules are those molecules which are functional in living systems or can interact with their components. A number of them are obtained from microbes such as organic acids, enzymes, cyclosporin A, and statins.

Organic Acids

Certain microbes have the ability to convert carbohydrates into organic acids. This capability of microorganisms is applied in the industrial production of some commercially important organic acids. A few very-important organic acids are as follows:

• Acetic acid: It is prepared from fermented alcohols with the help of acetic acid bacteria, Acetobacter aceti. Alcoholic fermentation by yeast is an anaerobic process, but the conversion of alcohol to acetic acid is aerobic one. It is used for the preparation of vinegar. It is also used in pharmaceuticals, coloring agents, insecticides, and plastic industries.
• Citric acid: It is obtained through fermentation carried out by fungi Aspergillus niger and Mucor species on sugary syrups. Yeast Candida lipolytica can also be employed, provided its nutrient medium is made deficient of iron and manganese. Citric acid is employed in dyeing, engraving, medicines, inks, flavoring, and preservation of food and candies.
• Gluconic acid: The acid is prepared by the activity of Aspergillus niger and Penicillium chtysogenum. Gluconate is used widely as a source of calcium for infants, cows, and lactating mothers.
• Lactic acid: It was the first acid to be produced by industrial fermentation. It is commercially produced from fermentable carbohydrates such as corn and potato starch, molasses, and whey by using bacteria Lactobacillus bulgaricus and L. delbrueckii.

Enzymes

Hardly 1.0-1.5% of the total known enzymes are employed in industry and medicine.

• Pectinases: These enzymes are obtained from fungi grown on pectin-containing medium. Examples are Aspergillus niget and Byssochlamys fulvo. These enzymes are used in enhancing juice extraction and clearing of juices.
• Proteases: Proteases are obtained from Mortierella renispora, Aspergillus, and Bacillus species. These enzymes are used in detergents to remove proteinaceous spots. Bottled juices are also clarified using protease and pectinase.
• Amylases: Amylases degrade starch. These enzymes are obtained from Aspergillus, Rhizopus, and Bacillus species. Amylases, glucoamylases, and glucoisomerases are employed in the conversion of corn starch into fructose-rich corn syrup.
• Streptokinase (tissue plasminogen activator or TPA): It is an enzyme obtained from the cultures of some hemolytic streptococci. It has fibrinolytic effect; it is used to dissolve blood clots in heart patients.

Cyclosporin A

• It is an 11-membered cyclic oligopeptide obtained through the fermentative activity of fungus Trichoderma polysporum.
• It has antifungal and anti-inflammatory properties. It is used as an immunosuppressive agent in organ transplant patients.

Statins

• Statins are the products of fermentation activity of yeast Monascus purpureus which resembles melonate and is the competitive inhibitor of B-hydroxy-ẞ-meth-ylglutaryl-CoA reductase (or HMG-CoA reductase).
• This competitively inhibits cholesterol synthesis. It is used as cholesterol lowering agent.

Microbes In Sewage Treatment

• Sewage is a collective noun used to represent municipal waste (both liquid and solid waste) generated in cities and towns which is carried off in sewerage.
• It contains large amount of domestic water and waste including human and animal excreta, microbes, and everything that enters sewerage system.
• Sewage or municipal waste should not be passed into rivers, streams, and other water bodies, because it not only contains human excreta and other organic wastes but a number of pathogenic microbes.
• It is made less polluted by passing it through STPs.
• The treatment of waste water is done by the hetero- trophic microbes naturally present in the sewage.
• The various steps in sewage treatment are as follows:
  • Primary treatment
    • It is the physical process of removal of large and small particles from sewage through sequential filtration and sedimentation.
    • Initially, floating debris is removed by sequential filtration. Then the grit (soil and small pebbles) is removed by sedimentation.
    • The sewage is first shredded and churned. It is then passed through many screens or skimmers to remove large pieces of organic matter. Now it is passed into a large primary settling tank having a gentle slope.
    • Grit, sand, and other heavy particles settle down.
    • All solids that undergo sedimentation of screened organic matter collectively consti- tute primary sludge.
    • Primary sludge can be used for preparing compost or manure directly. It can also be burnt.
    • The waste water (primary effluent) after removing the primary sludge contains fine organic matter. It is passed for secondary treatment.
  • Secondary treatment or biological treatment
    • It involves biological process of microbial degradation of organic matter.
    • There are three main methods: use of oxidation tanks, trickling filter method, and activated sludge method.
    • In activated sludge method, the effluent from primary settling tank is passed into an aeration tank. It is agitated mechanically.

• • • Air is pumped into the effluent. It contains a large population of aerobic heterotrophic microbes, including bacteria and fungi.
    • The microbes form flocs (masses of bacteria associated with fungal filaments).
    • The BOD (biological oxygen demand) of the effluent rises initially and the treatment continues till the BOD decreases to a certain level.
    • It is taken to secondary settling tank where the flocs undergo sedimentation.
    • The sediment is called activated sludge. (This can be the inoculant for the next sec- ondary treatment.)
    • The supernatant is allowed to pass into rivers and streams.
    • The activated sludge is taken to anaerobic sludge digesters along with the primary sludge.

• • • Here, anaerobic microbes act upon organic matter to first produce monomers and then organic acids.
    • This converts the latter into a mixture of gases such as methane, hydrogen sulfide, and carbon dioxide.
    • The gaseous mixture is called biogas. It is inflammable and can be used as a source of energy.
    • The spent sludge is used as manure and land fill or can be burnt. Pathogens present in the original sewage get killed during anaerobic digestion.
  • Tertiary treatment
    It is a physiochemical process in which chlorine gas, zirconium, ozone gas, perchlorate salts, UV rays, and reverse osmosis are used to remove DDT, pesticides, pathogens, and turbidity from waste water. It is preferred when water is to be used for domestic use.

River Action Plans

• Prior to 1985, very few cities and towns had STPs.
• Municipal waste water was discharged directly into rivers resulting in their pollution and high incidence of water borne diseases.
• In order to protect the major rivers of India from sewage pollution, the Ministry of Environment and Forests has initiated the development of STPs under the National River Conservation Authority. Examples are Ganga Action Plan (GAP), Yamuna Action Plan, etc.

Microbes In Production Of Biogas

• Biogas is a mixture of gases produced from degradable organic matter by the activity of various anaerobic bacteria.
• The microorganisms involved in biogas production are mainly facultative and strict anaerobic bacteria.
• The most important among them are methanogenic archaebacteria, represented by Methanobacterium.
• The other bacteria involved are Bacillus, Cellulomonas, Clostridium, and Ruminococcus.
• These bacteria are commonly found in anaerobic sludge formed during sewage treatment. Methanogens occur in the rumen of cattle where they act upon cellulose.

Composition of Biogas

• The major component of biogas is methane (about 50-70%), which is highly inflammable. The second major component is carbon dioxide (30-40%). The mixture of other gases (viz., H2, H2S, etc.) constitutes 10%.
• The calorific value of biogas is 4429 kcal/m3 at 50% methane content.

Commercial Production of Biogas

• The technology for biogas production was developed in India by IARI (Indian Agriculture Research Institute) and KVIC (Khadi and Village Industries Commission).
• A biogas plant has a large (10-15 ft. deep) concrete-or brick-lined air-tight cylindrical tank called digester.
• It has a charge pit for the passage of slurry into the digester, a floating gas holder of metal with an outlet for gas, and a pit for the removal of sludge or manure. The raw materials used in biogas plants are cattle dung, night soil, farm refuse, water weeds (e.g., Eichhornia), and other organic wastes.
• It is converted into slurry with 90% water content and fed into the digester.

• Cattle dung contains Methanobacterium and other methanogens which are normally present in the rumen of cattle for aiding the digestion of cellulose.
• An inoculum can also be provided when a gobar gas plant is to be initiated.
• The formation of biogas is a three-step anaerobic process:
  • Solubilization (decomposition)
    • Organic wastes are composed of lipids, proteins, cellulose, hemicelluloses, and lignin. In the first stage of biogas generation, facultative anaerobic decomposers are active.
    • They secrete hydrolytic enzymes, e.g., lipases, cellulases, proteases, and peptidases.
    • The enzymes break down the complex organic components into simpler and soluble substances. The latter are commonly called monomers.
  • Acidogenesis
    • Monomers are changed into organic acids with the help of fermentating microbes. The most common organic acid produced during acidogenesis is acetic acid.
    • Hydrogen and carbon dioxide are produced as by-products.
  • Methanogenesis
    • Methanogens or methane-producing bacteria become active.
    • They act on various components of microbial digestion and fermentation. Some important basic reactions are as follows:

Microbes As Biocontrol Agents

Biological Pest Control or Biopesticide

• Biopesticides are the organisms which are applied to destroy pests. These are used to destroy the weeds as well as the insect pests. Two basic types of biopesticides are bioherbicides and bioinsecticides.
• Transgenic plants are genetically engineered plants to develop resistance against pests. Examples are transgenic tobacco and transgenic cotton.
• Smoother crops are those crops which do not allow the weeds to grow nearby, e.g., barley, rye, Sorghum, millet, sunflower, alfalfa, soybean, marigold, etc. Smoother crops eliminate weeds through chemicals. Crop rotation with these crops will naturally reduce the incidence of weeds.
• Catch/trap crops: Around the major crop in the field, some early growing crop is sown in strips which is termed as catch or trap crop. The pests get attracted towards the early grown trap crop and then can be easily killed by cutting and destroying the trap crop. A good example of trap crop is bhindi (okra) which is sown around the cotton field to attract the jassid and spotted bollworm. Sesame is also a good trap crop to attract the red hairy caterpillar from the cotton field. Bioherbicides: These involve the biological control of weeds by some living organisms. For example, the use of insects feeding on a specific weed or the use of microorganisms which will cause diseases in weeds. Some common examples are as follows:
  • In India and Australia, the overgrowth of Opuntia (prickly pear cactus) was checked by the introduction of cochineal insect (Cactoblastis cactorum).
  • The first bioherbicide was a mycoherbicide called Devine. It was derived from a fungus Phytophthora palmivora which controls the growth of milk weed vines in Citrus orchards.
  • Another mycoherbicide called Collego has been derived from the conidia of fungus Colletotrichum gloeosporioides. It controls the growth of northern jointvetch (Aeschynomene virginica; family: Leguminosae) growing in rice fields.
  • The extensive growth of Hypericum perforatum or kalmath weed was checked in the USA by the introduction of Chrysolina beetles.
  • Water hyacinth has been successfully controlled in Florida using the indigenous fungus Cercospora rodmanii.
• Bioinsecticides: These are non-persistent, non-toxic, and biodegradable. These include the following:
  • Pathogens, parasites, and predators:
    • A well known example of biological control of an insect pest is the destruction of large populations of aphids (a pest on crucifers) by an insect called lady bug or praying mantis which feeds on aphids.
    • Hoverfly larvae (syrphid larvae) are very effective in keeping the aphids (plant bugs) under check as they feed on aphids only. Dragon flies are useful to get rid of aphids and mosquitoes.
    • Mosquito larvae are easily controlled by rearing the larvicidal fish Gambusia (mosquito fish).
    • Sugarcane scale insects are controlled by the coccinellid predators (Cailochorus negriti and Pharoscymnus homi); the fluted scale insect (Leerya purchasi), a common pest on Citrus trees, by the lady bird beetles (Rodolia cardinalis); and Nephantis serinopa, a dangerous pest on coconut palms, by Perisicrola nephanticdis and Trichospilus pupivora.
    • Baculoviruses are pathogens that attack insects and other arthopods. NPV (Nuclearpolyhedrovirus) based insecticide has been found to eliminate bollworms which cause extensive damage to cotton. It is species specific and has narrow spectrum.
    • Trichoderma species are effective biocontrol agents of several plant pathogens. Trichoderma species are free-living fungi that are very common in root ecosystems.
  • Sterilization strategy
    Screw worm (Cochliomyia hominivorax) was eradicated by releasing sterile males.
  • Insect hormone or pheromones
    • Pheromones are those chemical messengers which help in communication, sending alarm signals, marking trails, or attracting males.
    • These are secreted by females. Traps containing pheromones are placed in infected fields. Males attracted by the trap become unavailable for reproduction.
    • In confusion technique, the pheromone-containing papers are spread all over the field; so, males can no longer locate the females.
    • Introduction of molting hormone ecdysone or juvenile hormones at inappropriate times results in the early death of insect pests.
  • Natural insecticides
    • These are obtained from living organisms (plants). Examples are rotenones obtained from the roots of Derris elliptica; nicotine obtained from tobacco; pyrethrum and cinerin (pyrethroids) obtained from Chrysanthemum cinerarifolium); azadirachtin obtained from margosa (Azadirachta indica) leaves; and thurioside obtained from mutant strains of a bacterium called Bacillus thuringiensis (Bt).
    • Thurioside is a proteinaceous toxin and is ef fective against several insects such as moths, flies, mosquitoes, and beetles which accumulate as crystals inside the bacteria during sporulation.

Integrated Pest Management

• Sustainable pest management is otherwise known as integrated pest management (IPM), i.e., the integration of tactics for the control of a single pest on one or more crops.
• The overall objective of IPM is to create and maintain situations in which insects are prevented from causing significant damage to crops.

Microbes As Biofertilizers

• Organic farming is the raising of unpolluted crops through the use of biofertilizers that provide optimum nutrients to crop plants.
• Organisms that can be used to improve the nutrient quality of soil through biological activity are known as biofertilizers.
• The main sources are bacteria, cyanobacteria, and fungi. In paddy fields, cyanobacteria serve as an important biofertilizer.
  • Symbiotic N2 fixing bacteria such as Rhizobium leguminosarum fix atmospheric N2 in the root nodules of legumes.
  • Frankia (actinomycetes) fixes N2 in the root nodules of non-legume plants (e.g., Casuarina and Alnus).
  • Symbiotic cyanobacteria (blue green algae) such as Anabaena azollae fix atmospheric N2 in the leaves of Azolla (water fern). Azolla pinnata (a pteridophyte) is used as an excellent fertilizer in rice field.
  • Anabaena cycadae lives in the coralloid root of Cycas (a gymnosperm).
  • Aulosira is the most active, non-symbiotic nitrogen fixer in rice fields in India.
  • Free living nitrogen fixers such as Azospirillum and Azotobacter enrich the nitrogen content in soil.
  • Mycorrhiza: It is symbiotic association between the fungus and roots of higher plants (seed plants). Many members of genus Glomus form mycorrhiza. The fungal partner absorbs phosphorus from the soil and passes it to the plant. Plants having mycorrhizal associations show resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in growth and development. It is of two types:
    • Ectomycorrhizae (ectotrophic or ectophytic): Hyphae of fungus only form mantle on the outer surface of the root, increasing the absorption of water and minerals, e.g., Pinus, oak, etc. Mycorrhiza absorbs and stores nitrogen, phosphorus, potassium, and calcium.
    • Endomycorrhizae (endotrophic or endophytic): Fungal hyphae penetrate into cortex and cells of root, e.g., orchids, coffee, and woody plants. These are also called vesicular arbuscular mycorrhizae or VAM, because cortical cells swell and form vesicles or arbuscles. They play a significant role in providing phosphorus nutrition in plants.

 

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: Curd is more nutritious than milk.

Reason: LAB present in curd checks the growth of disease-causing microbes.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 2. Assertion: After 24 h, toddy becomes unpalatable.

Reason: Toddy left for a few hours undergoes fermentation.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 3. Assertion: Newer antibiotics are required to be produced regularly.

Reason: Pathogens often develop resistance to existing antibiotics.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 4. Assertion: Cyclosporin A is antifungal and immunosuppressive medicine.

Reason: It stimulates the activation of T-cells and prevents rejections.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 5. Assertion: Barley, sorghum, and millet are smoother crops.

Reason: They favor the growth of some common weeds.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 6. Assertion: Agricultural output increased several times after the introduction of DDT.

Reason: DDT was the first insecticide used on a wide scale.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 7. Assertion: The disadvantages of chemical pesticides can be overcome by the use of biopesticides.

Reason: Biopesticides are the harmless pesticides of biological origin which are used to control weeds and pests without causing any significant damage.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Strategies For Enhancement In Food Production

Animal Breeding

A group of animals related by descent and similar in most characters such as general appearance, features, size, and configuration are said to belong to a “breed.” Animal breeding is producing improved breeds of domesticated animals by improving their genotypes through selective mating.

Objectives of Animal Breeding

The main objectives of animal breeding are as follows:

• Improved growth rate.
• Increased production of milk, meat, egg, wool, etc.
• Superior quality of milk, meat, eggs, wool, etc.
• Improved resistance to various diseases.
• Increased productive life.
• Increased or, at least, acceptable reproduction rate, etc.

Methods of Animal Breeding

Two methods of animal breeding are inbreeding and outbreeding (based mainly on the breeding work done with cattle).

Inbreeding

• When breeding is done between animals of the same breed for 4-6 generations, it is called inbreeding, e.g., between the breeds of cows, buffaloes, poultry, etc.
• Inbreeding may be explained by taking an example of cows and bulls.
• Superior cows and superior bulls of the same breed are identified and mated.
• The progeny obtained from such mating are evaluated and superior males and females are identified for fur- ther mating.
• A superior female, in the case of cattle, is a cow that produces more milk per lactation.
• On the other hand, a superior male is a bull that gives rise to superior progeny as compared to that of other males.
• Inbreeding, as a rule, increases homozygosity.
• Thus, inbreeding is necessary if we want to develop a pure-line in any animal.
• Inbreeding exposes harmful recessive genes that are eliminated by selection.
• It also helps in the accumulation of superior genes and the elimination of less desirable genes.
• But continued inbreeding reduces fertility and even productivity.
• This is called inbreeding depression.
• In this condition, the selected animals of the breeding population should be mated with superior animals of the same breed but those which are unrelated to the breeding population.

Read and Learn More NEET Biology Notes

Outbreeding

• Outbreeding is breeding between unrelated animals. It may be between the individuals of the same breed (but not having common ancestors) or between different breeds (cross-breeding) or different species (interspecific hybridization).
  • Outcrossing: It is the mating of animals within the same breed but not having common ancestors on either side of their pedigree up to 4-6 generations. The offspring of such a cross is called an outcross. Outcrossing is the best breeding method for animals that are below average in productivity and milk production, growth rate in beef in cattle, etc. Sometimes only one outcross helps to over-come inbreeding depression.
  • Cross-breeding. In cross-breeding, the superior males of one breed are mated with the superior females of another breed. Many new animal breeds have been developed by this strategy. It gives better breeds. The cows of an inferior breed may be mated with the bulls of a superior breed to get better progeny. Hisardale is a new breed of sheep developed in Punjab by crossing Bikaneri ewes and Marino rams.
  • Interspecific hybridization: In this approach, the male and female animals of two different spe- cies are mated. The progeny obtained from such a mating are usually different from both parental species. But in some cases, the progeny may combine the desirable characters of both the parents. A mule is produced from a cross between female horse (mare) and male donkey. Mules are sturdier than their parents and are well-suited for hard work in mountainous regions.
• Animal husbandry is the science of rearing, improvement, and caring of domesticated animals.
• Although the word “animal” includes any of the various organisms belonging to kingdom Animalia, when we use it in animal husbandry, we mean only those domesticated animals which are reared mostly for economic or for recreation purposes, such as cattle, buffalo, sheep, goat, camel, pig, horse, etc.
• It also includes poultry farming and fisheries.
• Since a long time, animals such as bees and silkworm have been used by humans.
• All the above-mentioned livestock (animals kept for use or profit) has been used by humans for products such as milk, eggs, meat, wool, silk, and honey.
• The word “husbandry” means the management of do- mestic affair.
• The term used in connection with animal husbandry includes proper feeding, breeding, healthcare, hous- ing, etc.
• Domestication of animals probably began during the “hunting and gathering” phase of human civilization.
• As humans realized the importance of domesticating animals for use as beasts of burden and as sources of milk, meat, leather, and fur, the methods of improvement through selective breeding were used.
• Curiously, Old World agriculture employed animals while there is little evidence of the use of animals in the primitive agriculture of the New World.
• Most of the useful animals raised today have evolved from their wild ancestors.
• One of the earliest animals to be domesticated was the dog.
• Starting from a few basic types the wild dog, the wolf, and the jackal-man has produced an amazing variety of breeds. The Eskimos still use huskies to draw sledges.

Cattle Livestock

• Buffalo in India, termed “water-buffalo” in the Western literature, constitutes the most important species of livestock in India.
• It serves as the primary source of milk-the only dietary animal protein for a majority of Indians.
• Compared to cows, buffaloes (Bubalus bubalus) generally yield more milk of high fat content.
• They also have greater disease resistance and longevity.
• The milk yielding capacity of buffaloes is three times more than cows. Buffalo’s milk is superior to cow’s milk in fat content as well as minerals.
• The cattle are used to draw water from wells.
• Their dung is used as fuel and for the generation of biogas.
• India happens to be one of the largest exporters of leather goods made from cattle hide.
• Horns, hooves, and bones are used to prepare cattle feed and fertilizers.
• Indian cattle are hardy and highly resistant to major diseases.
• Bulls from India are used for cross-breeding with Eu- ropean and American varieties.
• The best Indian cattle breeds are found in the drier parts of the country.
• There are 26 breeds of cattle and 7 breeds of buffaloes which differ in their body colors, horns, and shape of forehead.
• The family of domestic cattle is Bovidae.
• There are two main groups of Bovidae (domestic cattle):
  • Bos indicus: It is found in India and Africa. It is also called zebu cattle or humped cattle.
  • Bos Taurus: It is found in Europe and North America. It is non-humped cattle.
• The zebu is characterized by the following:
  • Presence of prominent hump.
  • Upright horns.
  • A long face.
  • Drooping cars.
  • Large and slender legs.
• In the US, zebus are called Brahman cattle.

• The cattle breeds are classified into three groups.
  • Milch breeds: The cows of these breeds are good milk producers. However, bullocks are of poor quality.
  • Draught breeds: The bullocks of these breeds are good for working but cows are poor milk producers.
  • General utility breeds (dual-purpose breeds): The cows of these breeds are good milk producers and the bullocks are good draught animals. They are intermediate between milch and draught breeds.

Cross Breeds

• Karan Swiss: This breed has been evolved at the National Dairy Research Institute, Karnal, in Haryana, by breeding the Sahiwal cows with the semen of Brown Swiss bulls imported from the USA.
• Sunandini: This breed originated in Kerala by crossing the local non-descript cattle with Jersey, Brown Swiss, and Holstein-Friesian breeds.
• Karan Fries: This breed originated at the National Dairy Research Institute, Karnal, out of crossing between Tharparkar and Holstein-Friesian.

Cattle of Higher Altitudes

Mithun is found in the north-eastern India at an altitude of 700-1700 m. It is used for meat. Yak is found in Tibet, Ladakh, Lahaul, Spiti, Garhwal, and Sikkim. Yak gives meat, hide, and wool. It is also used for tilling land. The transport of people and goods across the desolate transHimalayan region would be impossible without the yak.

Cattle Management And Feeding

• India has about 227 million cattle and buffaloes. In terms of sheer numbers, India ranks fifth in the world. However, in milk production, India figures very poorly. Cattle management practices vary in different parts of the country depending upon climatic conditions. India is the lowest in milk yield per cow.
• Feeding: Ninety percent livestock subsists on grazing in public and government-owned lands and forests.
• The prepared feed given to them is classified into the following:
  • Roughages: These include fodder, silage, hag, and straw. This feed has a high fiber content.
  • Concentrates: These include cereals, millets, forage crops with high leaf protein and oil cake, oil seeds, and animal by-products. Although low in fiber content, the concentrates have high nutrient value and digestibility. Minerals and vitamins are added to the feed of high yielders. The proportion of balanced feed differs for the young and the adult animals.

Cattle-Breeding

• In villages, a few good pedigree bulls are selected on the basis of draught ability and permitted to graze with the cows to bring about random breeding. Bulls not selected for breeding are castrated when young and converted to bullocks. They are the main source of animal draught power in India.
• Mature cattle more than 3 years of age should be used for breeding. The best local cows with a good milk yield should be mated with a pure breed exotic bull which should have high genetic potential. One bull is usually enough for 60 to 70 cows.
• About 10-60% cows are artificially inseminated by semen collected from high-quality bulls. Artificial in- semination ensures good quality progeny and is also economical as semen from a single bull can inseminate several thousand cows. Average gestation period of the cow is 280 days. The length of gestation of buffaloes varies, influenced by breed and environment, between 276 and 340 days, but on an average, it lasts for 310 days (or 10 months), in contrast to the cow with an average gestation of 280 days (or 9 months).
• An average cow or buffalo produces 8-10 calves during its productive lifetime. Generally, only one ovum is fertilized at a time. Selective breeding and progeny testing and improvement take longer time in the live-stock than in annual food crops. With the exception of certain Indian breeds which have been maintained for good yield, the majority of Indian cattle has been on marginal inputs and is infertile and a poor milk yielder. Reasearch on the cause of infertility led to the use of pregnant mare serum gonadotropin to augment fertility in sterile cows and to induce lactation immature females by implantation of stilbesterol tablets.
• Artificial insemination (AI): It involves the insemination of the semen of superior bulls of exotic or indigenous breeds into native cows. The semen should be deposited either deep in the cervix or at the beginning of the body of the uterus. When insemination is performed deep in the cervix, the spermatozoa are likely to live longer in the cervix than in the uterus. The deposition of semen in the vagina results in dilution, contamination, and lowered conception rate. When a bull inseminates a cow naturally, approximately 5-10 billion spermatozoa are deposited in the vagina.
• However, when semen is deposited artificially into the cervix, considerably fewer sperms are required to achieve conception. Therefore, artificial insemination is very economical. Semen collected from a single superior bull can be used for fertilizing many cows. Semen from a desired bull located at a distant place can be used. The spread of certain diseases can be controlled by this method. Artificial insemination was first introduced in India at the Indian Veterinary Research Institute, Izatnagar, near Bareilly, Uttar Pradesh.
• To increase the milk yield, Indian cows are cross-bred with European breeds such as Holstein, Brown Swiss, Jersey, Red Dane, and others. Karan Swiss and Sunandini are the breeds developed through cross-breeding at the National Dairy Research Institute, Karnal, and in Kerala, respectively.
• Super ovulation and embryo transplantation: It is also called MOET (multiple ovulation and embryo transfer). A pedigreed bull and a high-production cow are chosen to produce super milch cows. Super ovulation is induced by hormone injection. After artifical insemination, 4 to 10 embryos are collected at a time. Each embryo is then transplanted into a “carrier” cow (surrogate mother).
• Such embryo transplants can also be carried out in sheep, goats, and other livestock. By deep freezing (-196 ̊C), it is possible to preserve seven days old fetuses for several years to be used when needed. An embryo can be cut into two, to obtain homozygotic twins. The most beneficial outcome of embryo transplantation is the selection of high-quality bulls for genetic upgrading. India has launched research using the above-mentioned techniques.

Use of Buffaloes

Buffaloes provide milk with all the essential nutrients. The milk has big-sized fat globules. It is rich in calcium and phosphorus and is low in sodium and potassium. Buffalo milk is almost free from carotenoids (golden yellow in color) due to the conversion of all carotenoid materials into vitamin A (colorless by the liver cells). Buffalo milk and ghee are white whereas ghee made from cow milk is golden yellow in color because of incomplete conversion of carotenoids into vitamin A inside the liver cells which ultimately appears in cow’s milk.

Cattle Diseases

• Most zebu cattle (domesticated cattle, Bos indicus) are resistant to diseases such as rinderpest or cattle plague and foot and mouth and other bacterial and viral diseases.
• Rinderpest has been controlled through a National Program.
• Vaccination is given to highly productive herds.
• Domesticated animals suffer from a variety of diseases.
• In animals, a disease may be defined as a state of discomfort associated with an abnormal function of the animals’ body.
• Diseases may be caused by mutant genes (genetic diseases), due to improper nutrition, or by pathogens.
• Genetic diseases are strictly selected against animal breeding.
• Generally, animals are raised on properly balanced diets to avoid nutritional disorders and to ensure optimum performance.
• Domesticated animals suffer from diseases caused by (a) viruses, (b) bacteria, (c) protozoa, (d) fungi, and (e) animals such as worms.
• Such diseases are commonly known as infectious dis- eases because these are caused by pathogenic infections.
• Many infectious diseases are known as contagious dis- eases since these spread to healthy animals by contact with diseased animals or with materials that were in direct contact with the diseased animals.
• Some infectious diseases may spread to humans from animals, e.g., anthrax.
• Infections can occur through skin, digestive tract, respiratory tract, conjunctiva, urogenital tract, placenta, umbilicus, udder, teats, and egg.
• It is a good policy to implement measures for the prevention of infectious diseases, some of which are as follows.
  • Isolation of animals suffering from or suspected to be infected with an infectious disease.
  • Proper disposal of the carcass and all materials that were in contact with the diseased animal(s).
  • Proper cleaning and disinfection of the animal house and other materials that were in contact with diseased animal(s).
  • Transfer of healthy animals to a pasture other than that used by diseased animal(s).
  • Vaccination of animals.
  • Injection of antiserum into healthy animals when- ever an epidemic is expected.
  • The authorities of the veterinary department should be immediately informed of cases of in- fectious diseases. This will allow them to initiate measures to prevent the spread of these diseases.

Bacterial Diseases

Animals suffer from several bacterial diseases. For example, cattle suffer from anthrax, mastitis, pneumonia, etc.

Anthrax

• Anthrax is caused by the bacterium, Bacillus anthracis.
• This disease is contagious and affects cattle, buffaloes, horse, sheep, and goats; it can also spread to human beings.
• In animals, anthrax spreads through contaminated food, water, and pastures.

Symptoms and Diagnosis

• In very acute cases, there is increased respiration and blood-mixed foamy discharge from mouth, nose, and anus.
• In such cases, the infected animals may die within minutes.
• But in subacute and chronic cases, the infected animals have high fever (up to 41.1°C) and increased pulse and respiration rates.
• There is discharge of black, shiny, and foamy material from the natural openings of animals.
• The infected animals die within 2 to 3 days.
• The anthrax bacterium uses up the oxygen carried by the animal blood.
• As a result, the animals die due to lack of oxygen.
• Disease diagnosis can be confirmed by microscopic observation of the bacterium in the blood of patients or by culturing the bacterium present in the blood on a suitable medium.

Treatment

• In case of human beings, a suitable antibiotic such as ciprofloxacin is quite effective, particularly if used in the initial stages of the disease.
• But in cattle, ciprofloxacin may be effective only in chronic cases.
• Anthrax antiserum can also be used with good results. In any case, antiserum should be given to all healthy animals to protect them from the disease.

Prevention and Control

• The general measures for the prevention of infectious diseases should be followed.
• Healthy animals should be vaccinated.
• Animals that have come in contact with diseased animals should be given anthrax antiserum to protect them from the disease.

Mastitis

Mastitis is the inflammation of udder that often occurs in dry cows due to the infection of bacterium Corynebacterium pyogenes.

Viral Diseases

Animals suffer from a variety of viral diseases. For example, cattle suffer from rinderpest, foot and mouth disease, cowpox, etc. In this section, rinderpest is discussed in detail.

Rinderpest

Rinderpest is caused by a virus. It is highly contagious. The virus is present in all the fluids and secretions of the body of the diseased animal. The disease spreads rapidly by direct contact with the diseased animal, through contaminated food and water, workers and their clothes, and by flies.

Symptoms

• Initially, the infected animal develops fever (40.0-42.2°C), loses appetite, develops constipation, and passes hard feces that are often covered with blood. In the final stages of the disease, the animal suffers from loose motions which give off offensive odor. The body temperature declines and may go down be- low normal. The animal usually dies in about 7 days.

Treatment

Treatment is effective only when it is started in the initial stages of the disease. The injection of sulfamethazine sodium is often effective. The injection of rinderpest antiserum is highly effec- tive, especially when combined with the injection of sulfamethazine sodium.

Prevention

All the measures for the prevention of infectious diseases should be implemented. It is highly desirable to vaccinate the animals against rinderpest. In 1954, a massive vaccination program was initiated in India. This project has been highly successful and rinderpest is no longer a dreaded disease.

Foot and Mouth Disease

• Foot and mouth disease affects cattle, sheep, goats, pigs, and other ruminants. It is caused by ssRNA Aphthovirus and is characterized by the eruption of vesicles over the lips; inside buccal cavity; and over legs, feet, udder, and even teats.
• There is a loss of appetite but dribbling of saliva is present. Lameness occurs.
• The infected animals should be separated immediately and the animal house should be thoroughly disinfected.

Cowpox

• Cowpox is a mild self-limiting eruptive skin disease of cows caused by cowpox virus. The infection is confined to udder and teats.
• It spreads to humans accidently while milking infected animals.
• Inoculum from cowpox lesions was used by Edward Jenner in 1798 as vaccine against smallpox.

Poultry

• Poultry-farming deals with the rearing of fowls (chicken), ducks, turkeys, and pheasants for their eggs and meat. India and the neighboring countries are recognized as the original home of the red jungle fowl (Gallus gallus). There is evidence that Aseel or Malay fowl were carried to Europe through the Middle East about 2,000 years ago. These have given rise to the present-day European breeds.
• Poultry and poultry products are a rich source of animal protein and other nutrients such as fats, vitamins, and minerals. The consumption of eggs would pave the way for overcoming protein malnutrition prevalent especially among the children in India.
• Poultry-farming has definite advantages over live- stock-rearing. Poultry birds are easy to raise, can be acclimatized to a wide range of climatic conditions, have short lifespan, and are prolific breeders. Hens have an average yield of 60 eggs per year (up to 240 eggs in high-yielding varieties). Poultry-farming requires less space, is easier to manage and maintain, and brings fast returns within a span of 6 months. In a poultry-farm, comfortable, well-ventilated, and illuminated dry houses are built. Birds of different ages are kept in separate houses. In regions with moderate climate, they are kept in cages (coops).
• The floor is littered with chopped straw, paddy husk, dry leaves, or groundnut hulls. It is made rat-proof and is provided with water channels with proper drainage. Minerals that are important for poultry diets are calcium, phos- phorous, sodium, copper, iodine, iron, manganese, and zinc. The vitamins required are vitamin A, B, E, pyridoxine, riboflavin, pantothenic acid, niacin, folic acid, B12, and choline. The male breeder’s diet should contain extra calcium, manganese, and vitamin E to ensure proper fertility. Thus, a balanced diet is the re- quirement so that utilization for the building of tissues and egg production is maximized. Clean and fresh water is very essential for birds.
• Light management: Light is essential for high egg production. 14 to 16 h of light including daylight is required for optimum production. When the pullets (young hens, especially at the time they begin to lay eggs) come into production, start giving additional light if the daylight is less than 12 h. Gradually increase the light 20 min every week till 16 h of total light is there. One tube-light of 40 W is sufficient for 36 m2 area while 40-W-bulb is sufficient for 18 m2 floor area. Light should spread uniformly. It should not be provided for the whole night.
• Fowls are widely distributed as domestic animals. The most common species of jungle fowls are Gallus gallus, G. lafayetti, and G. sonneratti
• Poultry feed includes all the nutrients. It is made of cereals and millets, oil cake, protein concentrates, fish and meat meal, minerals, and green vegetables. The domestic fowl (Gallus domesticus) population of our country can be roughly classified into two types:
  • Indigenous (desi type)
  • Exotic (improved type)
• Some indigenous breeds such as Aseel, Karaknath, Ghagus, Brahma, and Busra are the best table birds. The Aseel fowls are used in cock-fighting. The exotic breeds are classified, according to their source of origin, into American class, English class, Mediterranean class, and Asiatic class. Some examples are White Leghorn, Rhode Island Red, Plymouth Rock, and New Hampshire. These are now completely acclimatized to Indian conditions. Some of them are excellent egg- layers whereas others give good meat.

The indigenous breeds are crossed with the exotic breeds for improving egg production. Heterosis has been utilized for producing better egg layers and broilers (birds grown for meat) with high nutritive value.

Some diseases such as fowlpox, Ranikhet, coryza, fowl cholera, and aspergillosis take a heavy toll on poultry. But with better management, proper housing and nutrition, and timely vaccination of the chicks, these diseases can be controlled.

Ducks comprise 6% of the total poultry population in In- dia. They are abundant in the southern and eastern parts of India. There are 20 breeds of duck of which Muscori, Pekin, Aylesbury, and Campbell are popular exotic breeds; indigenous breeds include Indian Runner, Syhelt Meta, etc. Brown and white geese are common in India. Turkeys which are in demand during Christmas time belong to breeds Narfold, British White, Broad Breasted Bronze, and Beltsville Small White.

Poultry Diseases

• Encephalomalacia: Deficiency of vitamin E causes softening of brain tissue in young poultry.
• Coccidiosis: Protozoan Eimeria causes coccidiosis in fowls. It causes bloody diarrhea.
• Bacterial diseases: These are listed in Table 9.4.

Apiculture

• Apiculture is the care and management of honey bees. Honey bees give us honey and wax. They are good pollinators.
• The common breeds of honey bee are as follows:
  • Apis dorsata (rock bee)
  • Apis indica (Indian bee)
  • Apis florea (little bee)
  • Apis mellifera (Italian bee)
• Honey produced by the honey bee Apis species is probably the oldest sweetening agent in our civilization. Honey contains two sugars-dextrose and levulose and a mixture of several other substances. It is tasty, health-giving, and also medicinally useful. Honey bees also yield wax, which has multiple uses. A large quantity of honey is still collected from wild sources. However, bee-keeping (apiculture) using domesticated bees has been practiced in many parts of the world, including India (using 4. dorsata, A. florae, and A. indica).
• Social organization (castes) of honey bee: The nest of honey bee is known as bee-hive. The hive consists of 32 to 60 thousand individuals, showing a highly organized division of labor in the colony. Bees are polymorphic, consisting of three types of individuals (castes) viz. queen, drone, and worker.

• From its mandibular gland, the developing queen secretes antiqueen substances or antiqueen pheromones which inhibit the worker bees from building brood chambers and developing ovaries.
• Drones are male honey bees. They develop from unfertilized eggs. The phenomenon is called arrhenotoky. Drones and virgin queens take part in nuptial flight. After copulation, the drones are not allowed to come back into hive.
• The queen stores the sperm in her spermatheca. The material is sufficient to fertilize all the eggs that are laid by her.
• Females develop from fertilized eggs. Workers are sterile females. Scout bees search for food and intimate the same to worker bees by dances-round dance for less than 75 m and tail wagging dance for longer distances (Frisch).
• Workers have a pollen collecting apparatus in hind legs called corbicula and nectar storing mechanism in crop and wax secreting glands in abdomen.
• Young workers secrete royal jelly and are called nurse bees. Royal jelly is given to queen or potential queens. Apiculture is the rearing of bees or bee-keeping for collecting honey and wax.
• Honey is a near neutral sugary syrup with 6.8 pH, hav- ing 17-25% water, 3.3% minerals, abundant vitamins (B1, B6, C, D), L-fructose (laevulose, 41%), glucose (35%), sucrose (1.9%), and dextrin (1.5%). It is a tonic, a laxative, and a sweetening agent. Bee wax is secreted by the abdominal wax glands of the worker bees. It possesses a hardening substance from cephalic gland and a resin called propolis from pollen grains.

Fishery

• A large section of the Indian population uses fish as food. Fish is an easily available source of protein. It is highly nutritious and easily digestible. In India, edible fishes are abundantly available from sea, rivers, lakes, ponds, and marshes. Fish is also an item of ex- port trade.
• Fishes are reared in small rivers, lakes, and canals.
• Fish eggs are introduced into nurseries (hatcheries).
• The young ones hatched from the eggs are fed, tended, nursed, and harvested when full grown.
• Aquaculture techniques of induced breeding by the administration of pituitary hormones have helped in the production of seed fish in pure form.
• Hatcheries with circulating water have ensured almost 100% hatching of fertilized eggs.
• Culturing fish in fresh water is known as Inland fisheries.
• Fish industry also includes trapping and capturing fishes from estuaries, sea coast, and even from within the sea by using sophisticated electronic locaters, baits, nets, and trawlers.
• A large number of fishermen living in the coastal re- gions of India still use catamarans and various traditionally built boats.
• Mechanized fishing boats have now made deep-sea fishing possible.
• Catching, processing, and packaging of marine fishes have been developed on a scientific footing in our country.
• India exports marine food to several countries.
• Besides serving as table food, fishes are of medicinal value.
• Shark liver oil and cod liver oil are the natural sources of vitamins A, C, and D.
• Oils from sardines, herrings, and salmon are used in the manufacture of soaps and paints.
• Pisciculture is rearing, catching, and management of fishes.
• Culture fishery is the raising of fishes in tanks and ponds while capture fishery is the management of catching of fish without actually raising them.
• India has 1.6 million hectares of inland water (annual yield 2.242 million ton, 1996 data) and over 2.59 km2 of continental shelf for fishing (annual yield 2.7 million ton, 1996 data).

• Culture fishery: In this method, the pituitary hormone extract is injected into the male and female breeder fishes.
• Two males and one female are then kept in a breeding hapa a bamboo and cloth container.
• Spawning takes place in 3-6 h.
• Fertilized eggs are removed and kept in hatchery, where they hatch in 15-18 h.
• The hatchlings are kept in glass-jar hatcheries.
• A mouth is formed on the third day; the young fishes are now called fry.
• They are kept in rearing ponds for about 3 months where they grow into 4″-6″ long fingerlings.
• The fingerlings are then released into stocking ponds where they grow to the required size.
• In composite fish culture, different species of fish such as catla, rohu, and mrigal are cultured together.
• Types of ponds: Three types of ponds are required for the culture of the Indian major carps: nursery, rearing, and stocking ponds.
  • Nursery ponds: Efficient pond fish culture requires special preparation of nurseries to receive tender hatchlings at spawn. Small and seasonal nurseries are preferred as they facilitate effective control of the environmental conditions. The steps adopted towards the preparation of nurseries are the control of predatory fishes and weeds. There should be the production of zooplankton to serve as food for spawn and control of algal blooms.
  • Rearing ponds: The fries (sing. fry: young one of fish) are collected from the nursery ponds and are released in rearing ponds where they develop into fingerlings.
  • Stocking ponds: The fingerlings are netted out from the rearing ponds to the stocking ponds where they change to fishes. In the stocking ponds, the fishes are kept for stocking.
• Marine fisheries: Marine fisheries are divided into coastal fisheries (about 3 miles from the coast line) and deep sea fisheries (which have different fauna of fish). In India, about 75% of the marine fish catch is from the Western coast.
• The main marine fisheries are sardines (26%), mackerel (9.7%), and the Bombay duck (11%).
• Crustacean fisheries, i.e., prawns, lobsters, crabs, and Penaeus sp. are dominant on the West coast. Mollusc fisheries include oysters, clams, mussels, squids, cuttlefish, and octopus.
• Estuarine fisheries: The place where the fresh water of rivers meets the salt water of the sea is called an estuary. It contains brackish water.
• At estuary, only those fishes of fresh water and sea can survive that can tolerate a change of salinity.
• Estuary also forms the nursery ground for several marine and fresh water species.
• Fishing on large scale from such places results in the death of a number of young and immature fishes.
• Bag nets are most commonly used in estuarine fishery.
• The major estuarine systems in India are (a) Hooghly estuary in West Bengal, (b) Mahanadi estuary in Orissa, (c) Cauvery estuary in Tamil Nadu, (d) Narmada and Tapti estuary in Gujarat, and (e) Godavari-Krishna estuary in Andhra Pradesh.
• Carp fishes such as catla (theila), Labeo rohita (rohu), Cirrhinus mrigala (mrigal), and Labeo calbasu (kalbasu) are commonly cultured together in our country.
• Such a practice of culturing together of fishes is called polyculture or composite culture.
• Important edible fishes are as follows:
  • Fresh water fishes: Rohu (Labeo rohita), Calbasu (Labeo calbasu), Catla (Catla catla), Singhara (Mystus singhala), Magur (Clarias batrachus), and Singhi (Heteropneustes).
  • Marine fishes: Bombay duck (Harpodon sp.), Hilsa (Hilsa sp.), Eel (Anguilla sp.), Pomphret (Stromatetis sp.), Salmon (Aluitheronema sp.), and Sardine (Sardinella sp.).

Plant Breeding

• There are 12 mega-diversity centers in the world including India, having more than 65% global diversity. India has 7.7% genetic resources of the world.
• Agriculture originated in the Mesolithic age in New World and Old World.
• N.I. Vavilov, a Russian scientist, proposed eight cent- ers of origin of agriculture (now-a-days 12) called natural homes.
• India is the center of origin of 167 cultivated species and about 320 wild relatives of crop plants. A primary crop is a crop which came under domestication from the very beginning, e.g., wheat. Secondary crop was originally a wild relative of primary crop which was domesticated when primary crops failed.
• Monkombu Sambasivan Swaminathan (father of Green Revolution in India) initiated collaboration with Dr. Borlaug (father of Green Revolution) which reached the highest point (into the “Green Revolution”) through the introduction of Mexican varieties of wheat in India.
• Plant breeding is defined as the genetic improvement of a crop in order to create desired plant types that are better suited for cultivation, give better yields, and are disease resistant. Conventional plant breeding has been in practice since 9,000-11,000 years.

Main Steps in Plant Breeding

Following are the main steps in breeding a new genetic variety of a crop:

• Collection of variability: Collection and preservation of all distinct wild varieties, species, and relatives of cultivated species is a pre-requisite for the effective exploitation of natural genes available in the population. Germplasm is the sum total of all alleles of the genes present in a crop and its related species.
  The entire collection (of plants/seeds) having all diverse alleles of all genes in a given crop is called germplasm collection. A good germplasm collection is essential for a successful breeding program. Therefore, germplasm collection is the most practical and effective answer to problems such as loss of germplasm due to expansion of agriculture, industries, and other hu- man activities.
• Evaluation and selection of parents: The germplasm is evaluated to identify plants with desirable combination of characters. The selection of parents is done by picking up the seeds of only those plants for multiplication which have the desired traits.
• Common methods of crop improvement
  • Selection: It is of three types:
    • Mass selection: It is the simplest and the oldest method mainly for cross-pollinated crops and is based on phenotypic characters. The varieties produced by this method loose desirable qualities.
    • Pure line/inbred selection: It involves isolating desirable homozygous individuals and is done for self-pollinating crops, e.g., wheat varieties PV-18, HUW-468, and Kalyan Sona.
    • Clonal selection: It is used for vegetatively reproducing crops, e.g., Kufri Safed potato.
  • Hybridization: It may be of the following five types:
    • Intravarietal (useful for self-pollinated crops)
    • Intervarictal (intra-specific), e.g., Ganga and Ranjit varieties of maize
    • Interspecific: Rice variety ADT-37 (Oryza ja- ponica Oryza indices)
    • Intergeneric, e.g., triticale, Raphanobrassica
    • No new characters are created by hybridiza- tion.
  • Mutation breeding: Various chemicals such as HNO2, base analogs, alkylating agents, acridine dyes, X rays, UV rays, and gamma rays are used to induce mutations which produce desirable qualities. It has been used commonly in self- pollinating crops. A number of new varieties have been developed such as the following:
    • Sharbati Sonora and Pusa Lerma varieties of wheat (formed the basis of Green Revolution in India).
    • Reimei and Atomita-2 varieties of rice.
    • Erectiferum and Erectoids varieties of barley.
    • Aruna variety of castor.
    • Thick shell in ground nut (TGI).
    • Wheat-NP 836
    • Rice-Jagannath
    • Cotton-Indore-2
    • In mung bean, resistance to yellow mosaic virus and powdery mildew.
    • Peppermint (Menthe piperita); Todd’s Mitcham variety (high oil content and disease resistant)
  • Polyploid breeding: Induced polyploidy is used by plant breeders for improving the yield of for- age and other crops. Many modern day crops such as wheat, rice, sugarcane, and cotton are natural polyploids. Allopolyploids have been used for obtaining fertile hybrid between different species and genera. Allopolyploidy leads to the immediate formation of new species. For example, durum wheat, bread wheat, and triticale.
• Selection and testing of superior recombinations: The selection process yields plants that are superior to both the parents. These plants are self-pollinated for several generations till they come to a state of uniformity (homozygosity), so that the characters will not separate in the progeny.

• Test, release, and commercialization of new cultivars: The newly selected lines are evaluated for their yield and other agronomic traits of quality, disease resistance, etc. This evaluation is done by growing these in the research field and recording their performance in ideal fertilizer, irrigation, etc. The testing of materials is done in the farmer’s fields, for at least three growing seasons at different locations in the country, representing all agroclimatic zones.
  India is an agricultural country. Agriculture contributes about 33% of India’s GDP and gives employment to about 62% of the population. The development of several high yielding varieties of wheat and rice in 1960 increased the yields per unit area. This phase is often called Green Revolution.
  • Wheat and rice: From 1960 to 2000, wheat pro- duction increased from 11 million ton to 75 million ton while rice production increased from 35 million ton to 89.5 million ton. This was due to the development of semi-dwarf varieties of wheat and rice.
    • Dwarf wheat: A dwarfing gene, Norin-10, was reported in Japan. American plant breeders produced single dwarf wheat. N. Borlaug of Mexico produced triple dwarf wheats, popularly known as Mexican wheats. These had high yield, resistance for lodging and common pathogens and pests, and smaller growth period. Sonora-64 and Lerma Rojo-64 were brought to India and modified through gamma mutations to make them the part of Indian agriculture. In 1963, many lines like Sonalika and Kalyan Sona were also selected as high yielding and disease resistant varieties.
    • Dwarf rice: A dwarfing gene, dee-geo- woo-gen, was reported in Taiwan. It was introduced in the rice varieties by IRRI, Philippines, in varieties IR-8 and IR-24. Taichung Native-1 developed from Taiwan Jaya and Ratna were developed in India.
  • Sugarcane: Saccharum barberi was originally grown in North India, but had poor sugar content and yield. Saccharum officinarum had higher sugar content and thicker stems but did not grow well in North India. These two species were crossed to obtain sugarcane varieties combining the desirable qualities of high sugar, high yield, thick stems, and ability to grow in the sugarcane belt of North India.
  • Millets: Hybrid bajara, jowar, and maize have been developed in India. From hybrid varieties, the development of several high yielding varieties resistant to water stress has been possible.

Plant Breeding For Disease Resistance

Fungal, bacterial, viral, and nematode pathogens attack cultivated crops. Due to this, there is 20-30% loss in crop yield. In such situation, if the crops are made disease resistant, food pro- duction will increase and the use of fungicides and bactericides would be reduced.

Some Important Fungal Diseases of Economically Important Plants

• Phycomycetes
  • Peronospora – Downy mildew
  • Pythium aphanidermatum – Damping off of seed- lings
  • Phytophthora infestans – Late blight of potato
  • Sclerospora graminicola – Green ear disease of bajra
• Ascomycetes
  • Claviceps purpurea – Ergot of bajra
  • Erysiphe Powdery mildew
• Basidiomycetes
  • Puccinia graminis tritici – Stem rust or black rust of wheat
  • Puccinia recondite – Leaf rust or brown rust of wheat
  • Ustilago hordei – Covered smut of barley
• Deuteromycetes
  • Alternaria solani – Early blight of potato
  • Cercospora personata – Tikka disease of groundnut
  • Colletotrichum falcatum – Red rot of sugarcane 14. Fusarium udum – Wilt of arhar
  • Helminthosporium oryzae – Sesame leaf spot or brown leaf spot of rice

Methods of Breeding for Disease Resistance

Breeding is carried out either by conventional breeding techniques described earlier or by mutation breeding. The conventional method of breeding for disease resistance is hybridization and selection. The various sequential steps are as follows:

• Screening germplasm for resistance sources
• Hybridization of selected parents
• Selection and evaluation of hybrids
• Testing and release of new varieties

New varieties having these desirable characters can either be multiplied directly or can be used in breeding. Other breeding methods that are used are mutation, selection among soma- clonal variants, and genetic engineering.

Plant Breeding for Developing Resistance to Insect Pests

Insect and pest infections are two major causes of destruction of crop plants and crops. Insect resistance in host crop plants is due to morphological, biochemical, or physiological characters. For example, solid stem in wheat leads to non-preference by the stem sawfly; smooth leaved and nectarless cotton varieties do not attract bollworms; and low nitrogen, sugar, and high aspartic acid in maize develops resistance to maize stem.

The sources of resistance genes may be cultivated varieties, germplasm collections of the crop, or wild relatives of the crop.

Plant Breeding for Improved Food Quality

It is estimated that more than 840 million people in the world do not have adequate food to meet their daily requirements. Three billion people suffer from proteins, vitamins, and micronutrient deficiencies because they cannot afford to buy adequate vegetables, fruits, legumes, fish, and meat. Breeding of crops with higher levels of vitamins and minerals or higher protein and healthier fats is called biofortification.

Plant breeding is undertaken for improving the nutritional quality of plants. The objectives are as follows:

• Protein content and quality
• Oil content and quality
• Vitamin content
• Micronutrient and mineral content

Wheat variety with high protein content (Atlas 66) has been used as a donor for improving cultivated wheat.

Indian Agricultural Research Institute (TARO), New Delhi, has developed many vegetable crops that are rich in minerals and vitamins. For example, vitamin A enriched carrots, pump- kin, and spinach; vitamin C enriched bitter gourd, bathua, to- mato, mustard, and calcium; iron enriched spinach and bathua; and protein enriched beans (broad lablab and French and gar- den peas).

Breeding for Anti-Nutritional Factors

Anti-nutritional factors are compounds present in foods that have adverse effect on animal and human growth. Some exam- ples are as follows:

• Glucosinolates are present in oils obtained from Brassica napus and are not liked by animals. Similarly, crude acid (long-chain saturated fatty acids) produces heart ailments.
• A neurotoxin, cyanoalanine, present in khesari (Lathyrus sativus) produces muscular cramps and causes lathyrism (a type of paralysis).

Crops should be free from such anti-nutritional factors. Canola is a variety of rapeseed in which genes for glucosinolates and erucic acid have been deleted.

Single-Cell Proteins

Some microorganisms such as bacteria, blue green algae, yeasts, and filamentous algae are used as food. These are called single- cell proteins (SCP). These are processed to remove excess nu- cleic acid, e.g., Spirulina, Fusarium graminearum, Chldella, Methylophilus methylotropus (source of Pruteen; 250 g of this microorganism can be expected to produce 25 ton of protein), Scenedesmus.

Tissue Culture

Plant cells and organs can be cultured in vitro on a suitable medium. Haberlandt started the technique of plant tissue culture in 1902.

The culture medium can be liquid, semi-solid, or solid. It contains source of carbon and energy (sucrose), minerals, glycine, vitamins, and growth regulators (auxin such as 2-4 D and cytokinin such as BAP).

The plant part used for tissue culture is called explant. The explant and media are sterilized before culturing. Explants are sterilized by specific antimicrobial chemicals (surface sterilization) and vessels, and media instrument with steam, dry heat, or alcohol.

Callus Culture

A small piece of parenchymatous tissue is introduced over cul-ture medium in a tube or flask in dark at 200-25°C. Within 4-6 weeks, it forms actively growing irregular and undifferentiated mass called callus. It is divided into several small sections and is sub-cultured. Each piece is then allowed to “differentiate into plantlets by providing light and morphogenetic growth hormones.

Multiple Shoot Production

It is used for raising numerous pathogen-free copies of rare plants, hybrids, and sterile plants. A shoot tip or bud with 1-4 leaf primordia is sterilized and introduced over the cul- ture medium with high salt content and naphthalene acetic acid (NAA). At an interval of 4-6 weeks, the shoot tip is given cuts or shaken to form more buds. When new plants are required, the buds are transferred to low-salt culture medium devoid of NAA. Each bud gives rise to a small plantlet.

Suspension Culture

In this technique, an explant is suspended into liquid medium containing growth regulator and is constantly agitated at the speed of 100-250 rpm (revolutions per minute). Agitation serves the following three purposes:

• Aeration of culture
• Constant mixing of medium
• Breakage of cell aggregates into smaller groups

Suspension cultures grow much faster than callus cultures. In both types of tissue cultures, with passage of time, cell/tis- sue dry matter increases and the level of nutrient decreases. To prevent the damage of newly-formed cells, parts of the cultures are regularly transferred to new culture vessels containing fresh media. This process is termed as sub-culturing.

Shoot Tip Culture or Production of Disease-Free Plants

Pathogen-free clones of plants can be obtained through shoot- tip culture because shoot apical meristem is usually free of pathogens (including virus) due to high concentration of auxins and rapid rate of cell division.. Apical meristem accompanied by 1-2 leaf primordia is taken. For this, the apical bud is steri- lized. The shoot tip is now placed over the culture medium-un- der aseptic conditions.

Somatic Embryo Regeneration

Somatic embryos are those that arise from somatic cells in tissue culture. The pattern of development of a somatic embryo proceeds through globular, heart-shaped, and torpedshaped stages and mimics the development of sexually produced embryos. Somatic embryo regeneration is induced by high con- centration of auxin. These embryos are also used to produce synthetic/artificial seeds by encapsulating them in alginate.

Embryo Culture

Embryo culture involves the exclusion of young embryo from seeds and their cultivation through tissue culture. Embryo culture has the following applications:

• In embryo rescue: Interspecific hybrids are often sterile because of embryo mortality and seed collapse. In such cases, the hybrid embryo is excised from the female parent in early stage and is cultured, e.g., common bean (Phaseolus vulpris) and wild bean (P. augustissimus).
• Embryo culture allows seeding development in plants whose seeds lack stored nutrients required for seedling growth, e.g., orchid.
• It is also used in some rare plants such as makapunonuts.

Haploid Culture/Androgenic Haploid Culture/Pollen Grain Culture

Haploid culture technique was developed by Guha and Maheshwari (1964) in Datura innoxia. Floral buds which are very young and unopened are first sterilized in Clorox for 20-40 min. These are then opened to remove anthers. Anthers are introduced over culture medium. Within 4-6 weeks, each anther gives rise to a number of haploid embryoids. Normally haploid culture produces sterile haploid plants. Colchicine treatment results in chromosome doubling and produces homozygous diploids for each and every trait. Gynogenic haploids are also possible by using unfertilized ovules.

Winter wheat Jinghua-1 and rice Guan-18 are two important varieties that are produced by this and are now under cultivation.

Uses of Androgenic Haploid

• It is useful in mutation breeding.
• Androgenic haploid is pure for its characters.
• Every gene can express in the plant.

Protoplast Fusion/Somatic Hybridization/Parasexual Hybridization

Protoplast fusion is the fusion of cells of two plants belonging to different varieties, species, and even genera. The cells are first treated with enzymes pectinase and cellulase.

These enzymes dissolve the cell walls and, as a result, naked protoplasts are produced. These protoplasts are fused by electrofusion (high-frequency alternating electric field with short current pulses) and chemofusion [through sodium nitrate or PEG (polyethyleneglycol)]. This results in hybrid protoplasts. The hybrid cell may have a synkaryon (single fused nucleus) or a heterokaryon (having two unfused nuclei).

The hybrid protoplast is called cytoplasmic hybrid or cybrid if one of its two nuclei gets degenerated. The first somatic hybrid was obtained by Carlson et. al. (1972) between Nicotiana glauca and N. langsdorfi species of tobacco. The intergeneric somatic hybrids are pomato (potato x tomato) and bomato (brinjal x tomato).

Applications of Tissue Culture

• Tissue culture can be applied for crop improvement.
• It can be applied for the rapid multiplication of desirable and rare plants.
• It can be applied to obtain indefinite number of plants.
• It can be applied to obtain virus-free plants from shoot арех.
• Somaclonal variations: These variations are produced during tissue culture. Some of these may be useful and stable, e.g., better yield and quality, male sterility, early maturation, resistance to diseases and pests, etc. Significant variations that have been taken up in plant breeding are high protein content and resistance to late blight in potato, increased shelf life in tomato, resist- ance to rust and high temperature tolerance in wheat, resistance to tungro virus and leaf hopper in rice, short duration in sugarcane, etc.

 

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: Bulls not selected for breeding are castrated when young and converted to bullocks.

Reason: They are the main source of animal drought power in India.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 2. Assertion: Anthrax is caused by a bacterium.

Reason: Anthrax develops only in buffaloes and cannot be transferred to humans.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 3. Assertion: In anthrax, the animal dies due to lack of oxygen.

Reason: The anthrax bacterium uses up the oxygen carried by the animal blood.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 4. Assertion: Cattle breeds can be improved by super ovulation and embryo transplantation.

Reason: Super ovulation in high milk yielding cows is induced by hormonal injection.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 5. Assertion: Honey is an animal product produced by honey bee.

Reason: Honey contains only sugar, nothing else.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 6. Assertion: India ranks fifth in the world in catile population but figures poorly in milk production.

Reason: Buffaloes give more milk with higher fat and mineral contents than cows.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 7. Assertion: Poultry farming has definite advantage over livestock rearing.

Reason: Poultry birds are easy to raise, can be acclimatized to a wide range of climatic conditions, have short lifespan, and are prolific breeders.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 8. Assertion: Encephalomalacia, a disease of poultry, is caused by the protozoan Eimeria.

Reason: Encephalomalacia causes bloody diarrhea in poultry.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 9. Assertion: Fish meal is a rich source of protein for cattle and poultry.

Reason: Fish meal is prepared from the non-edible parts of fishes such as tails, fins, and bones.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 10. Assertion: Somatic hybrids may be used for the production of useful plants.

Reason: Genetic manipulation can be carried out more rapidly when plant cells are in protoplast state.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 11. Assertion: Callus is obtained within 2-3 weeks.

Reason: Suspension culture grows much faster than callus culture.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 12. Assertion: Genetic improvement of the crop is plant breeding.

Reason: It creates desired plant types that are better suited for cultivation.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 13. Assertion: The phase between 1960-1970 is often called the Green Revolution.

Reason: The development of several high yielding varieties of wheat and rice in 1960’s increased yields per unit area.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 14. Assertion: The maize having high nitrogen, sugar, and aspartic acid is resistant to pest.

Reason: It develops resistance to maize root borers.

Answer. 4. If both Assertion and Reason are false, then mark (4).

NEET Biology Notes – Evolution Introduction

• The theory of evolution maintains that the different kinds of organisms that we see today have evolved from common ancestors over millions of years.
• This theory is one of the most important concepts in biology.
• The distinguished scientist Theodosius Dobzhansky has said, “Nothing in biology makes sense except in the light of evolution.”
• For more than a century, the theory of evolution has exerted a very strong influence not only on our thinking about biology, but also on developments in other disciplines such as sociology, politics, economics, and religion.
• Life originated on the earth between 3000 and 4000 million years ago in the form of unicellular organisms.
• How did these simple cells lead to (or evolve into) organisms as large as a whale or a Sequoia (redwood) tree and structures as complex and delicate as the eye and the brain?
• The theory of evolution by natural selection was put forward by Charles Darwin and Alfred Russel Wallace towards the middle of the 19th century.
• It has provided us with a scientific framework for understanding the evolutionary changes that have occurred and continue to take place in the biological world.

From Origin Of Earth To Origin Of Life

• Evolution is a slow, continuous, and irreversible process of change.
• Origin of earth: The big bang theory proposes that the universe had an explosive beginning. The universe originated about 20 billion years ago by a big bang (thermonuclear explosion) of a dense entity. About 4.6 billion years ago, our solar system was probably created when the gaseous cloud called solar nebula started to collapse under the force of its own gravity, until it became a flattened spinning disc of atoms and particles. Its central region heated up and became a star.
• The earth is about 4.6 billion years old, and the oldest rocks that have persisted in recognizable form are about 3.8 billion years old. For many years, scientists believed that such ancient rocks did not contain any fossils, but they knew that fossils were simply too small to be seen clearly without an electron microscope.
• The oldest microfossils discovered so far are that of cyanobacteria that appeared 3.3-3.5 billion years ago.
• Massive limestone deposits called stromatolites became frequent in the fossil record about 2.8 billion years ago. Produced by cyanobacteria, stromatolites were abundant in virtually all freshwater and marine communities until about 1.6 billion years ago.
• The fossil records indicate that unicellular protists the first eukaryotes-appeared about 1.5 billion years ago.
• The basic unit of evolution is population.
• According to recent literature, the first non-cellular forms of life could have originated 3 billion years ago. These were giant molecules (RNA, protein, polysac- charides, etc.). These capsules reproduced their molecules perhaps. The first cellular form of life did not possibly originate till about 2000 million years ago.

Read and Learn More NEET Biology Notes

Theories On The Origin Of Life

• Theory of special creation: It states that life was created by supernatural power in the form that has not undergone any change. It was given by Father Suarez. God created life in six days from materia prima and man was created by Him on the sixth day. According to this theory, the earth is about 4000 years old.
• Theory of catastrophism: It was given by Cuvier. According to him, after a gap of certain period (called age), the world undergoes a catastrophe (sudden calamity) that kills almost all living organisms and then God creates a new generation or new life from inorganic matter.
• Theory of biogenesis (i.e., life from life, omnis vivum ex vivo): This theory was proved by Redi, Spallanzani, and Pasteur independently. They disproved (refuted) the theory of spontaneous generation (abiogenesis). Francesco Redi (1668) proved that flies could not arise from putrefying meat without their eggs. Spallanzani (1767) demonstrated that the putrefaction of meat is due to microbes in the air and it can be prevented by boiling and sealing the meat in air-tight containers. Pasteur gave a definite proof of life arising from pre- existing life using microbes and sterilization methods. He performed “swan neck flask” experiment.
• Cosmozoic theory (theory of panspermia): This theory was given by Richter (1865) and Helmholtz (1884) and supported by Arrhenius (1908). They suggested that life reached the earth from some heavenly body through meteorites. According to this theory, panspermia (primitive form of life, as suggested by Arrhenius) consisted of spores or seeds (sperms) and microbes that existed throughout the universe and produced different forms of life on this earth.
• Abiogenic or Chemical Origin of Life
  Majority of scientists are of the opinion that life originated from inanimate matter. Since the theory of abiogenic origin or chemi- cal evolution of life is the only one that provides an explanation that can be tested, most scientists have tentatively accepted it.

Oparin-Haldane Hypothesis

• Alexander I. Oparin (1894-1980), a Russian bio- chemist, and J.B.S. Haldane (1892-1964), a British scientist, put forward the concept that the first living organism evolved from non-living material. They also suggested the sequence of events that might have oc- curred. In 1923, Oparin postulated that life originated on the earth at some point of time in the remote past and under the conditions no longer observed. In his book, The Origin of Life (1938), Oparin submitted “abiogenesis first, but biogenesis ever since.” Oparin’s theory is known as primary abiogenesis.
• According to Oparin and Haldane (1929), the sponta- neous generation of early molecules might have taken place if the earth once had more reducing atmosphere compared to the present oxidizing atmosphere. Oparin and Haldane agreed that the primeyal earth contained little, if at all, oxygen. Perhaps in the primitive atmos- phere, oxygen in the free gaseous state was virtually absent. Therefore, no degradation of any organic com- pound arising in the primeval earth could have taken place.
• As there was no ozone layer in the atmosphere, any absorption of UV radiations, which is lethal to our pre- sent lives, was not possible in the primeval earth.
• The early gas cloud was rich in hydrogen, being pre- sent in the combined form in methane (CH), ammonia (NH3), and water vapor (H2O).
• Moreover, the atmospheric water vapor along with early gas cloud condensed into drops of water and fell as rain that rolled down the rock surfaces and accumu- lated to form liquid pools and oceans. In the process, the erosion of rocks and the washing of minerals (e.g., chlorides and phosphates) into the oceans were inevi- table. Thus, Haldane’s hot dilute soup was produced and the stage was set for the combination of various chemical elements.
• Atmospheric chemicals and those in water produced small precursor molecules such as amino acids, sugars, and nitrogenous bases. These precursor molecules then combined resulting in the appearance of proteins, polysaccharides, and nucleic acids.
• The energy sources for such reactions of organic synthesis were the UV radiations (solar radiation), cosmic rays, electrical discharges (lightning), intense dry heat (volcanic eruption), and radioactive decay of various elements on the earth’s surface. Once formed, the organic molecules accumulated in water because their degradation was extremely slow in the absence of any life or enzyme catalysts. Such transformation is not possible in the present oxidizing atmosphere because oxygen or microorganisms will decompose or destroy the living particle that may arise by mere chance.

Experimental Evidence for Abiogenic Molecular Evolution of Life

• Harold C. Urey (1893-1981), an astronomer, accorded the first adequate recognition of Oparin-Haldane’s view on the origin of life in 1952.
• Urey asked his student Stanley L. Miller, a biochemist, to replicate the primordial atmosphere as propounded by Oparin and Haldane.
• Miller (1953) made the first successful simulated experiment to assess the validity of the claim for the origin of organic molecules in the primeval earth’s conditions.

• The abiotic synthesis of biomolecules is studied under the following headings:
  • Chemogeny: It is the synthesis of organic molecules by chemical reactions.
  • Biogeny: It is the formation of self-replicating biomolecules in broth (primordial hot soup or warm little pond).
  • Cognogeny: It is the evolution of various forms of life or the diversification of existing groups.

Enclosing the Prebiotic Systems

• The experiments of Miller and other scientists demonstrate that prebiotic molecules could have been formed under the conditions which most likely existed on the early earth.
• Still, the formation of prebiotic soup of small molecules does not necessarily lead to the origin of life.
• For the origin of life, at least three conditions needed to have been fulfilled:
  • There must have been a supply of self-replicators, i.e., self-producing molecules.
  • Copying of these replicators must have been subject to error via mutation.
  • The system of replicators must have required a perpetual supply of free energy and partial isolation from the general environment.
• The high temperature prevailing in the early earth would have easily fulfilled the second condition, that is, the requirement of mutation. The thermal motion would have continually altered the prebiotic molecules.

Evidences Of Evolution

Evidences from Anatomy

• Homologous organs
  • These organs have similar basic structure and developmental origin.
  • The organisms that possess such organs are said to have originated from common ancestor.
  • Consider, for example, the seal’s flipper, the bat’s wing, the horse’s foot, the cat’s paw, and the human’s hand.
  • In plants, a thorn of Bougainvillea differs from a tendril of Cucurbita in its function; both are located in a similar (auxiliary) position and have similar origin.
  • Thorns and tendrils are considered homologous.

• • Homologous organs show divergent evolution. It means that similar structures developed along different directions due to adaptions to different needs or adaptive radiation (which is the development of dissimilar functional structures in closely related group of organisms).

• Analogous organs
  • These are organs that are not anatomically similar though they perform similar functions.
  • For example, the wings of birds and butterfly look alike; they perform the similar function of flying but are not anatomically or structurally similar.
  • Even the wings of birds and bats are also analogous structures which have different origins.
  • Other examples are the flippers of penguin and dolphin (the former is a bird and the latter is a mammal), and the eyes of octopus and mammals (both differ in retinal position; still the function is the same).
  • In plants, sweet potato (root modification) and potato (stem modification) is another example of analogy. Both are meant for the storage of food but are modifications of different parts of plant.
  • Now, what is the reason of the development of analogous structures?
  • The possible explanation may be that it is the similar habitat that has resulted in the selection of similar adaptive features in different (distantly related) groups of organisms put toward the same function.
  • This phenomenon is termed as adaptive convergence or convergent evolution. It is the opposite of adaptive radiation as seen in homologous structures.
• Vestigial organs
  • These are believed to be the remnants of organs that were complete and functional in the ancestors.
  • The study of vestigial organs offers an evolutionary explanation of such rudimentary vestiges by stating that adaptations to the new environment of the organism have made these structures redundant.
  • Such structures are called vestigial organs.

• • The rudiment of the reptilian jaw apparatus and the rudiments of the hind limbs of python and Greenland whales are some examples of vestigial organs.
  • In humans, many vestigial structures indicate a relationship with other mammals, including the primates.
  • For instance, the muscles of the external ear and scalp are rudimentary and often non-functional.
  • But these are common to many mammals where they are functional.
  • The reduced tailbone and nictitating membrane of the eye, the appendix of cecum, rudimentary body hair, and wisdom teeth are examples of vestigial organs.
  • The appendix of man is thought to be a remnant of the large cecum-the storage organ for cellulose digestion in herbivorous mammals.
  • Similarly, the non-functional vestiges of the pelvic girdle in python and porpoise show, for instance, that they originally evolved from four-footed ancestors.
• Atavism
  • The sudden reappearance of an ancestral character is called atavism.
  • For example, tail in new born human baby.
  • The winged petiole of Citrus represents that the unifoliate condition is derived from the trifoliate leaf.

Biogeographical Evidences

• The study of the patterns of distribution of animals and plants in different parts of the earth is called biogeography.
• Alfred Russel Wallace (1823-1913) divided the whole world into six major biogeographical regions or realms.

• • Palaearctic: Europe and Asia, north of the tropics, north-western corner of Africa, including the Atlas Mountains.
  • Nearctic: North America exclusive of the tropics, Alaska, Canada, United States, and Mexico.
  • Neotropical: Central America including low lands of Mexico, islands of the Caribbean, and all of South America.
  • Ethiopian: Africa (with exception of the Atlas Mountains) and Madagascar and adjacent islands.
  • Oriental: Tropical part of Asia (including India); south of the Himalaya Mountains; and eastward through Sumatra, Java, Borneo, and Philippines.
  • Australian: Australia; Tasmania; New Guinea; and all islands of the Indonesian archipelago that lie to the east of Borneo; beginning with Celebes.
• Biogeographic map of the world is that in which the six major biogeographic realms are present.
• Geologists believe that millions of years ago, all continents we demarcate today were in the form of a single land mass.
• On account of geological changes, especially the movements of crustal plates below the surface of the earth, huge land masses broke off and drifted apart from one another.
• As these land masses (continents) moved away, the seas separated them and acted as barriers to the free movement of organisms among the continents.
• Because of variable environmental conditions prevailing on the different continents, over centuries, plants and animals evolved independently in each biogeographical region.
• Consider, for example, two instances that show similarities in the pattern of distribution of plants and animals between two land masses which were once the part of a larger land mass.
  • The flora and fauna on each of the Galapagos Islands a chain of 22 islands in the Pacific Ocean on the west coast of South America-resemble those of the South American mainland with which the Galapagos Islands were once connected.
  • Magnolias, tulips, and sassafras are found naturally growing in the eastern USA and in China. Hence, these show disjunct distribution. This means that these floras have different groups that are related but widely separated geographically.
• The distribution patterns of the present-day animals and plants as well as fossils are best explained on the basis of the theory of evolution.
• The birds on Galapagos Islands show differences in bills and feeding habits.
• The bills of several of these species resemble those of different, distinct families of birds on the mainland.
• All these birds are thought to have evolved from a single common ancestor.

What is Adaptive Radiation?

• During his journey, Darwin went to Galapagos Islands. There he observed an amazing diversity among creatures.
• Of particular interest were small black birds, later called Darwin’s finches, which amazed him.
• He realized that there were many varieties of finches on the same island.
• All the varieties, he conjectured, evolved on the island itself.
• From the original seed-eating features, many other forms with different sizes of beaks arose, enabling them to become insectivorous and vegetarian finches.
• These birds on the Galapagos Islands show difference in bills and feeding habits, but still resemble the birds present on the original mainland.
• Hence, we have seen that different species have evolved from single common ancestor.

• This process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation, of which Larwin’s finches represent one of the best example.
• The clusters of species that have been formed on the Galapagos Islands (Tasmanian wolf) are clear examples of species formation arising by microevolutionary divergence from an ancestral form occupying different habitats of microevolution leading to macroevolution.
• Another example is Australian marsupials.

• A number of marsupials, each different from the other, evolved from an ancestral stock but within the Australian continent.
• When more than one adaptive radiation appears to have occurred in isolated geographical areas (representing different habitats), one can call this convergent evolution.
• Placental mammals in Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals each of which appears to be similar to a corresponding marsupial (e.g., placental wolf and Tasmanian wolf marsupial)

Embryological Evidences

• The sequence of embryonic development in different vertebrates shows striking similarities.
• Gill clefts and notochord appear in the embryonic development of all vertebrates from fishes to mammals.
• The notochord is replaced by the vertebral column in all adult vertebrates.
• Similarly, gills are replaced by lungs in adult amphibians, reptiles, and mammals.
• Such similarities in embryonic development once again reinforce the idea of evolution from common ancestors.
• Occasionally, embryonic features such as tail and gill slits persist in adults.

• According to Ernst Haeckel, ontogeny (development of embryo) is the recapitulation of phylogeny (the ancestral sequence).
• This view was summarized by his biogenetic law: Ontogeny recapitulates phylogeny.
• Developmental evidence for evolution is also available from plants.
• It is generally believed that mosses and ferns are more evolved than algae.
• Protonema of mosses resembles certain green algae.
• This provides a clue to their evolutionary relationship.
• Both bryophytes and pteridophytes have ciliated sperms and require water for fertilization.
• Gymnosperms do not need water for fertilization.
• But Cycads and Gingko, the primitive gymnosperms, have ciliated sperms like pteridophytes.
• This suggests that gymnosperms have descended from pteridophyte-like ancestors.
• The occurrence of ancestral traits in embryo is called palaeogenesis.

Palaeontological Evidences

• Fossils are the remains and/or impressions of organisms that lived in the past few centuries. Palacontologists have painstakingly built up extensive collections of fossils from all over the world.
• Fossil record has helped in building the broad historical sequence of biological evolution.
• Phylogeny, the evolutionary history of the organism, can sometimes be reconstructed with the help of fossils.
• Horse, elephant, and man are good examples of relatively complete reconstructions of phylogeny.
• Besides form and structure, the habits and behavior of extinct species can be inferred from well-preserved fossils.
• It is also possible to reconstruct the entire habitat of an organism from fossils.
• Fossils also indicate the connecting links between two groups of organisms.
• Archaeopteryx shows the features of both reptiles and birds.

• The reptilian characters of Archaeopteryx are as follows:
  • The body axis is more or less lizard-like.
  • A long tail is present.
  • The bones are not pneumatic.
  • The jaws are provided with similar teeth.
  • A weak sternum is present.
  • Free caudal vertebrae are present as found in lizards.
  • The hand bears typical reptilian plan and each finger terminates in a claw.
• The avian characters of Archaeopteryx are as follows:
  • Feathers are present on the body.
  • The two jaws are modified into a beak.
  • The forelimbs are modified into wings.
  • The hindlimbs are built on the typical avian plan.
  • There is an intimate fusion of the skull bones as seen in the birds.
• By careful analysis of the distribution of fossils in different strata of rocks, the time in history when different species were formed or became extinct can be inferred.

Timeline of Evolution

• When scientists first began to study and date fossils, they had to find some way to organize the different time periods from which the fossils came.
• They divided the earth’s past into large blocks of time called eras.
• Eras were further subdivided into smaller blocks of time called periods, and some periods, in turn, were subdivided into epochs.
• The major geological eras, with their approximate dates in millions of years.

Fossil Parks

• Our country has rich deposits of fossil plants spanning a gap of 3500 million years.
• 20 million years old fossil forests have been discovered and studied by the Birbal Sahni Institute of Palaeobot any, Lucknow. These forests need to be systematically studied and conserved for scientific understanding and enlightenment. Some excellent localities that can be raised to the status of national fossil parks are as follows:
  • 50 million years old fossil forests preserved in the sediments between the streaming lava flow that poured out into the Deccan country at Mandla district, Madhya Pradesh.
  • 100 million years old fossil forest located in Raj-mahal Hills, Bihar.
  • 260 million years old coal-forming forests in Orissa.

Microfossils and Fossil Fuel Exploration

1. Paleobiological study helps in understanding and locating coal and hydrocarbon sources.
2. Palynofossils-tiny microscopic spores, pollen, and other vegetal remains of the past-assist us in inter- preting ancient environmental conditions favorable for organic matter accumulation and its conversion to fossil fuels by transformation and subsequent thermal alteration.
3. By the quantitative analysis of microfossils, it is possible to determine the approximate location and con- figuration of nearshore marine deposits, which are in turn responsible for the formation and accumulation of hydrocarbons.
4. The main sources of hydrocarbons are phytoplankton, marine, and terrestrial algae as well as lipid-rich plant remains.
5. Thus, the study of fossil plants offers an effective tool in stratigraphic geology and can be exploited in tapping organic fuel resources.

Evolution Of Modern Horse

Eohippus (Hyracotherium)

• The evolution of modern horse began in Eocene epoch.
• The first fossil named Eohippus (dawn horse) was in North America.
• This horse was about the size of a fox or terrier dog (a type of small dog for unearthing foxes), only 40 cm high at the shoulders.
• It had short head and neck.
• The forelimbs were with four complete fingers (2, 3, 4, and 5) and one splint of the first finger and the hindlimbs with three functional toes (2, 3, and 4) and one splint of the fifth toe. (Splints are non-functional reduced fingers and toes of horse.)
• Teeth were with incomplete cement.
• Molar teeth had no serrations.
• Low-crowned molar teeth were adapted to browse soft lush vegetation.

Mesohippus

• Mesohippus, the intermediate horse, evolved from Hyracotherium about three crore years ago during Oligocene epoch.
• It was of the size of modern sheep, about 60 cm high at the shoulders.
• Forefeet had three fingers and one splint of the fifth finger and hind feet possessed three toes, but the middle one was longer than the others and supported most of the body weight.
• Molar teeth had some serrations.

Merychippus

• Merychippus, the ruminating horse, arose from Mesohippus in Miocene epoch about two crore years ago.
• It was of the size of a small pony, about 100 cm high at the shoulders.
• It had a longer neck.
• Its forelimbs and hindlimbs had three fingers and three toes, the middle finger and toe being longer than the others and supported the entire body weight.
• There was no splint.
• Teeth were longer with cement.
• Molar teeth had well-developed serrations.

Pliohippus

• Pliohippus, the Pliocene horse, evolved from Merychippus in Pliocene epoch about one crore years ago. It was the size of modern pony, about 120 cm high at the shoulders.
• Its every forelimb and hindlimb had one complete finger and one complete toe and two splints hidden beneath the skin.
• Pliohippus is, therefore, referred to be the first one toed horse.
• The molar teeth were long with well-developed cement and serrations.
• Teeth were adapted for eating grass.

Equus

• Equus is the modern horse that arose from Pliohippus in Pleistocene epoch about nine to ten lakh years ago in North America and later spread throughout the world except Australia.
• It is about 150 cm high at the shoulders.
• It has a long head and a long neck.
• Each forelimb and hindlimb of the modern horse has one finger and one toe and two splints.
• The crowns of molar teeth are elongated with enameled ridges and are highly suitable for grinding.
• During the evolution of horse, there was
  • General increase (with occasional decrease) in size,
  • Progressive loss of toes,
  • Lengthening of toes that were retained,
  • Lengthening of limbs in general,
  • Enlargement of brain, especially cerebral hemi- spheres,
  • Increase in height, and
  • Increase in the complexity of molar teeth and an enlargement of the last three premolars until they came to resemble molars.

Evolution of Vertebrates and Major Groups of Plants

• The patterns of evolution of vertebrates and major groups of plants are conspicuously different.
• The major groups of vascular plants have left relatively small number of fossils which even show gaps (fossil-less dark periods).
• There are relatively a few major lineages, and all lineages are very distinct from one another.
• Instead of showing gradual and continuous change through time, the major lineages appeared suddenly in the fossil record.
• After that, they persisted with little fundamental change for hundreds of millions of years.
• The existence of many major subdivisions of vascular plants living today can be recognized about 345 mil- lion years ago on the basis of their distinctive reproductive structure.
• All primitive land plants reproduce via tiny spores contained in the sporangia. The major taxonomic groups are distinguished by the position of sporangia on the plant.
• The sporangia are terminal, located at the tip of the plant in the most primitive Psilopsida.
• These are placed at the base of the leaves in Lycopsida (represented in the modern flora by Lycopodium and Selaginella).

• The sporangia are arranged in whorls at the top of the plant in Sphenopsida (horsetails).
• Fossil evidences document that these basic patterns have been maintained for more than 350 million years. A few, if any, intermediates are known between these patterns.
• The origin of seeds in the land plants was achieved about 345 million years ago in lineages recognized as ancestral to all more advanced vascular plants.
• The last major evolutionary advancement among vascular plants was the emergence of flowering plants (the angiosperms) about 140 million years ago.
• But the fossils left no clue as to their ancestors.
• The fossil records also indicate that nearly all living orders of angiosperms and most of the characters of their modern-day representatives evolved from them.
• The continuous change of a character within an evolying lineage is termed as evolutionary trend.
• A lineage is an evolutionary sequence arranged in linear order from an ancestral group to a descendant group.
• The number of trends in any lineage is, therefore, the same as the number of characters evolving.
• A trend may be progressive (simple to complex, from unicellular to multicellular) or retrogressive (complex to simple from bacteria to virus).

Brief Accout Of Evolution

• About 2000 million years ago (mya), the first cellular forms of life appeared on earth.
• The mechanism of how non-cellular aggregates of giant macromolecules could evolve into cells with membranous envelop is not known.
• Some of these cells had the ability to release O2.
• The reaction could have been similar to the light re- action in photosynthesis where water is split with the help of solar energy captured and channelized by appropriate light harvesting pigments.
• Slowly, single-celled organisms became multi-cellular life forms.
• By about 500 mya, invertebrates were formed and active.
• Jawless fishes probably evolved around 350 mya.
• Sea weeds and a few plants were existent probably around 320 mya.
• We are told that the first organisms that invaded land were plants.
• They were widespread on land when animals invaded land.
• Fishes with stout and strong fins could move on land and go back to water.
• There are no specimens of these left with us.
• However, these were ancestors of modern day frogs and salamanders.
• The amphibians evolved into reptiles.
• These lay thick-shelled eggs that do not dry up in the sun unlike those of amphibians.
• Again, we only see their modern day descendentsturtles, tortoises, and crocodiles.
• This was about 350 mya.
• In 1938, a fish caught in South Africa happened to be a Coelacanth which was earlier thought to be extinct.

• These animals called lobefins evolved into the first amphibians that lived on both land and water.
• In the next 200 million years or so, reptiles of different shapes and sizes dominated the earth.
• Giant ferns (pteridophytes) were present but they all fell to form coal deposits slowly.
• Some of these land reptiles went back into water to evolve into fish-like reptiles probably 200 mya (e.g., Ichthyosaur).
• The land reptiles were, of course, the dinosaurs.
• The biggest of them-Tyrannosaurus rex-was about 20 ft in height and had huge fearsome dagger-like teeth.
• About 65 mya, dinosaurs suddenly disappeared from the earth.
• We do not know the true reason.
• Some say climatic changes killed them. Some say most of them evolved into birds.

• The truth may lie in between.
• Small-sized reptiles of that era still exist today.
• The first mammals were like shrews.
• Their fossils are small sized.
• Mammals were viviparous and protected their unborn young inside the mother’s body.
• Mammals were more intelligent in sensing and avoiding danger at least.
• When reptiles came down, mammals took over this earth.
• In South America, there were mammals resembling horse, hippopotamus, bear, rabbit, etc.
• Due to continental drift, when South America joined North America, these animals were overridden by North American fauna.
• Due to the same continental drift, the pouched mammals of Australia survived because of lack of competition from any other mammal.
• Lest we forget, some mammals live wholly in water. Whales, dolphins, seals, and sea cows are some examples.
• Evolutions of horse, elephant, dog, etc., are special stories of evolution.
• The most successful story is the evolution of man with language skills and self-consciousness.

Theories Of Evolution

Lamarck’s Theory of Evolution

• Lamarck’s theory is often called as the theory of inheritance of acquired characters or the theory of use and disuse of organs.
• The first attempt to explain the origin of species and their adaptation to the environment was done by Jean Baptiste Lamarck (1744-1829).
• He was the greatest French naturalist.
• Lamarck’s theory was published in 1809 (year of Darwin’s birth) in his book “Philosophie Zoologique.”
• According to this theory, organisms undergo changes to adapt themselves to the environment.
• The changes acquired by organisms during their lifetime are passed on to the next generation.
• He took the example of long neck of Giraffe. They continuously stretched their neck to reach the vegetation on trees.
• This acquired change was passed on to the next generation.
• He also gave the principle of use and disuse.
• The use of an organ will lead to strengthening of the organ, and disuse will lead to weakening of the organ.
• Lamarck arranged his theory in the form of four postulates.
  • Internal forces tend to increase the size of the body.
  • The formation of new organs is the result of the need or want continuously felt by organisms Doctrine of appetency/desires.
  • The development and power of action of an organ is directly proportional to its use.
  • All changes acquired by the organism during its life are transmitted to the offsprings by the process of inheritance.

Darwin’s Theory of Evolution

• Charles Robert Darwin put forward the concept of natural selection as the mechanism of evolution.
• The theory was put forward along with Alfred Russell Wallace.
• Darwin had written the book “Origin of Species.”
• Darwin was greatly influenced by “An Essay on Population” written by Thomas Rev Malthus. He was also influenced by Charles Lyell’s essays on “Principles of Geology.”
• Darwin was a British naturalist.
• In 1831, at the age of 22, he was appointed on a world survey ship of British government, HMS Beagle.
• For five years on this ship, Darwin explored the fauna and flora of continents and islands.
• Branching descent and natural selection are the two key concepts of the Darwinian theory of evolution.
• According to Wallace’s chart, the main points of Dar- win’s theory of natural selection were as follows:
  • High rate of reproduction
  • Total number almost constant
  • Struggle for existence
  • Variations
  • Survival of fittest
  • Natural selection
• All successful organisms have a high biotic potential or reproductive rate.
• The organisms produce a large number of offsprings that can possibly survive.
• For example, a mouse produces a dozen mice at a time. A rabbit produces six young ones in a litter (there are four litters in a year). A rabbit starts reproducing at the age of 6 months.
• Not all but only some individuals that survive reach adulthood, and those which reach adulthood, reproduce at different rates. This is called differential reproduction.
• The success in survival and reproduction depends on the characteristic traits of an organism. For example, only those rabbits will survive which are the fastest. There is “struggle for existence” and, in this, there will be “survival of the fittest.” The phrase “survival of the fittest” was first used by Herbert Spencer. The same context was asserted by Darwin as “natural selection.”
• So, evolution is the change in the genetic composition of the population which is brought about by natural selection (which acts upon the variability in population).

Causes of Variations

• Mutation is the ultimate source of variations.
• At the next level is recombination.
• Intermingling of two widely separated populations also causes variation.

Weakness of Darwinism

• He was not able to explain the cause of discontinuous variations observed by him in nature and the mode of transmission of variants to the next generation.
• In 1868, Darwin put forward the theory of pangenesis. According to this theory, every organ of the body pro- duces minute hereditary particles, called pangenes or gemmules, and these are carried through the blood into the gametes.
• Weismann’s theory of germplasm (1892) rejected Darwin’s theory of pangenesis.
• He established that the germ (sex) cells are set apart from other body (somatic) cells early in the embryonic development. So, only the changes in the germplasm affect the characteristics of future generations.
• Alfred Wallace (1823-1923), a naturalist from Dutch East Indies, was working on Malay Archipelago (present Indonesia).
• He had written the book “On the Tendencies of Varieties to Depart Indefinitely from the Original Type.”

Mutation Theory

• In 1901, Hugo de Vries proposed the mutation theory on the basis of his observation on a wild variety of evening primrose, Oenothera lamarckiana.
• According to this theory, new species originate as a result of large, discontinuous variations that appear suddenly.
• The main features of mutation theory are as follows:
  • Mutations arise from time to time amongst individuals of a naturally breeding population.
  • Mutations are heritable and establish new forms or species.
  • Mutations are large and sudden and are totally different from the fluctuating variations of Darwin, which are small and directional.
  • Mutations may occur in any direction.

Hardy-Weinberg Principle

• The five basic processes that affect the Hardy-Wein- berg equilibrium and cause variations at genetic level are as follows:
  • Mutation.
  • Gene migration
  • Genetic drift
  • Recombination
  • Natural selection
• The Hardy-Weinberg principle states that the proportions of different alleles will stay the same in a large population if mating occurs at random and the above mentioned forces are absent.
• In algebraic terms, the Hardy-Weinberg principle is written as an equation.
• Its form is what is known as a binomial expansion.
• For a gene with two alternative alleles, A and a, the frequency of allele A can be expressed as p and that of alternative allele a as q. Because these are the only two alleles, p + q must always be equal to one. The equation looks like this:
• For example, if q is the frequency of allele a, then the Hardy-Weinberg equation states that q2 is the percentage of individuals homozygous for allele a, say 16%. q2=0.16,q=0.4

Mutation

Replica Plate Experiment of Lederberg and Lederberg

• Mutations are random (indiscriminate) with the respect to the adapative needs of organisms.
• Most mutations are harmful or with no effect (neutral) on the bearer.
• Mutation rates are very slow.
• The Lederberg replica plating experiment, a beautiful example of the genetic basis of a particular adaptation, was demonstrated in bacteria by an ingenious method devised by Joshua Lederberg and Esther Lederberg.

• E. coli bacteria are usually grown in the laboratory by plating dilute suspensions of bacterial cells on semi-solid agar plates.
• After a period of growth, discrete colonies appear on the agar plates.
• Each of these colonies originates from a single bacterium through a large number of cell divisions.
• They then created several replicas of this master plate by a simple procedure.
• A sterile velvet disc, mounted on a wooden block, was gently pressed on the master plate.
• Some bacteria from each colony adhered to the velvet.
• By pressing this velvet on to new agar plates, they obtained exact replicas of the master plate, because the few bacteria transferred by the velvet formed colonies on the new agar plates.
• However, when they attempted to make replicas using plates containing an antibiotic such as penicillin, most colonies found on the master plate did not grow on the replica plates.
• The few colonies that did grow were obviously resistant to penicillin.
• How did the bacteria acquire the ability to grow in a new environment (here, agar medium, containing penicillin)? In other words, what was the origin of this adaptation?
• A Lamarckian interpretation of this adaptation would have been that penicillin somehow induced a change in one or more bacteria, enabling them to grow in the presence of penicillin.
• A Darwinian view is that there were, in the original suspension of bacteria from which the master plates were prepared, a few bacteria carrying mutant genes which conferred on them the ability to survive the action of penicillin and form colonies.
• These mutations, which had arisen by chance and not induced by penicillin, were present only in small numbers in the original suspension.
• Lederberg’s experiment provided evidence that mutations are actually preadaptive.
• These kinds of mutations are regarded as advantageous mutations.
• These appear without exposure to the environment.
• Actually, preadaptive mutations express themselves only after exposure to the new environment to which the organisms are to adapt themselves.
• The new environment does not induce the formation; it only selects the preadaptive mutations that occurred earlier.

Migration

• Migration, defined in genetic terms as the movement of individuals from one population into another, can be a powerful force in upsetting the genetic stability of natural populations.
• If the characteristics of the newly arrived animal differ from those already there, the genetic composition of the receiving population may be altered, if the newly arrived individual or individuals can adapt to survive in the new area and mate successfully.
• Gene pool: The total collection of all genes and their alleles in a population is called gene pool. Thus, gene pool will have all genotypes, i.e., genes of the organisms.
• Gene flow: If genes are exchanged between two different populations of a species, it is gene flow.

Genetic Drift/Sewall Wright Effect/Non-Directional Factor

• Natural selection is not the only force responsible to bring about changes in gene frequencies. There is the role of chance or genetic drift also.
• Genetic drift causes a change in gene frequency by chance in a small population.
• In a small population, the individual alleles of a gene are represented by a few individuals in the population.
• These alleles will be lost if these individuals fail to reproduce.
• Allele frequencies appear to change randomly, as if the frequencies were drifting genes. Thus, a random loss of alleles in small population is genetic drift.
• A series of small populations that are isolated from one another may come to differ strongly as a result of genetic drift.
• Genetic drift has following two ramifications:
  • Bottle-neck effect:
    • It is the decrease in genetic variability in a population, e.g., cheetah population in Africa decreased due to hunting.
    • Their decreased numbers have limited cheetahs’ genetic variability, with serious consequences.
    • The present cheetah population is susceptible to a number of fatal diseases.
    • If any of these diseases attacks the cheetah population, the path of extinction of cheetah cannot be reversed.
  • Founder’s effect:
    • When one or a few individuals are dispersed and become the founders of a new, isolated population at some distance from their place of origin, the alleles that they carry are of special significance.
    • Even if these alleles are rare in the source. population, they will be a significant fraction of the new population’s genetic endowment.
    • This effect by which rare alleles and combinations of alleles may be enhanced in new populations is called founder’s effect.
    • Founder’s effect is particularly important in the evolution of organisms on islands such as Galapagos Islands which Darwin visited. . Most of the kinds of organisms that occur in such areas are probably derived from one or a few initial founders.
    • Fixation of new mutations: Genetic drift fixes new alleles-genes that arise by mutation-from time to time and eliminates the original gene, thereby changing the genetic makeup of small population.

Recombination

• Gene recombination is also an important source of variation.
• It occurs during crossing-over at the time of meiosis [free assortment (selection) of genes at the time of gamete formation], random union of gametes at the time of fertilization, and even chromosomal aberrations.
• They cause reshuffling of gene recombinations which provide new combinations of existing genes and alleles.
• This is the entity of gene recombination.
• Gene recombination can occur not only between genes but also within genes resulting in the formation of a new allele.
• Since it adds new alleles and combination of alleles to the gene pool, it is an important process during evolution which causes variations.

Natural Selection

• Natural selection causes allele frequencies of a population to change. Depending upon which traits are favored, natural selection can produce different results.
• Forms of selection: There are three kinds of natural selections:
  • Stabilizing selection (normalizing selection): When selection acts to eliminate both extremes from an array of phenotypes, the frequency of the intermediate type which is already the most com- mon is increased.
  • Directional selection (progressive selection): When selection acts to eliminate one extreme from an array of phenotypes, the genes determining this extreme become less frequent in the population. Industrial melanism in peppered moth, Biston betularia, provides good example of directional selection from nature.
  • Disruptive selection (diversifying selection): In some situations, selection acts to eliminate, rather than favor, the intermediate type. Individuals at both extremes are favored.

Examples of Natural Selection

Industrial Melanism

• Industrial melanism was first studied by R.A. Fisher and E.B. Ford and, in recent time, by H.B.D. Kettlewell.
• One of the most striking example which demonstrates the action of natural selection is the industrial melanism in England.

• The peppered moth, Biston betulania, with a dull gray color or white color was abundant in England before the Industrial Revolution.
• A black-colored form of the same moth (melanic, a dominant mutant differing in a single gene), carbon- aria, was very rare.
• Within a couple of hundred years, however, the proportion of carbonaria increased to almost 90%.
• These moths rest on tree trunks.
• Before the Industrial Revolution, the tree trunks used to be covered with gray-colored lichen.
• The dull gray moth easily blended with this back-ground, while the black moth stood out conspicuously and was, therefore, more susceptible to predation by birds.
• With the advent of the Industrial Revolution, large-scale burning of coal became common.
• The enormous amount of smoke produced resulted in the deposition of particulate matter on tree trunks, turning them black.
• As a result, the gray moths now became more conspicuous than the black variety and, hence, more susceptible to predation.
• The frequency of black-colored moths in the population, therefore, increased.
• Gradual replacement of coal by oil and electricity as well as the improved methods of controlling soot production reduced the soot deposition on the trees.
• Conditions then became more suitable for the survival of gray moths. Consequently, their frequency once again increased.
• Thus, reduction in pollution is now correlated with reverse evolution.
• Industrial melanism, as this phenomenon is called, is thus a particularly interesting example which clearly brings out the action of natural selection.
• This has been observed in about 70 different species of moths, and in several other European countries as well.
• This understanding is supported by the fact that in areas where industrialization did not occur, e.g., in rural areas, the count of melanic moths was low.
• This showed that in a mixed population, those that can better-adapt, survive and increase in population size. Remember that no variant is completely wiped out. Similarly, excess use of herbicides, pesticides, etc., has only resulted in the selection of resistant varieties in a much lesser time scale.
• This is also true for microbes against which we employ antibiotics or drugs against eukaryotic organisms/cell.
• Hence, resistant organisms/cells are appearing in a time scale of months or years and not centuries.
• These are examples of evolution by anthropogenic action.
• This also tells us that evolution is not a direct process in the sense of determinism.
• It is a stochastic process based on chance events in nature and chance mutations in the organisms.

Change in Genotypic Frequencies

• If the alleles for gray and black colors are denoted by G and B, respectively, the genotypes of moths would be GG, GB, and BB.
• Since B is dominant, GB and BB will be black.
• Due to greater predation by birds on the black (melanic) phenotype, the proportion of B in the population was maintained at a much lower value than that of G.

Resistance of Mosquitoes to Pesticides

• Mosquitoes have always been a major health hazard, especially as they are responsible for the spread of diseases such as malaria and filaria.
• When DDT was first introduced to control mosquitoes, it was tremendously successful; most mosquitoes were sensitive to DDT and were, therefore, killed.
• However, DDT has now become ineffective against mosquitoes.
• This is explained as follows:
  • In the original population of mosquitoes, some individuals were resistant to DDT.
  • In the absence of DDT, such resistant individuals were few because they had no advantage over the DDT-sensitive mosquitoes.
  • However, when DDT was used on a large-scale, only resistant genotypes were able to survive and reproduce.
  • As a result, over a period of time, almost entire population came to consist of the resistant type, which made DDT quite ineffective.
• Evolution is, thus, a change in gene frequencies in a population in response to changes in the environment-in this case, the introduction of DDT.
• The principle of natural selection, thus, helps us to understand why such chemical insecticides would remain useful only for a limited time.

Artificial Selection

• Some genetic variability is always present in a population.
• Some alleles make organisms better adapted to the environment and, thus, make them more successful in survival and reproduction.
• As a result, the frequency of such alleles in a population gradually increases.
• This is called selection; these alleles are, thus, “selected” over the other alleles.
• This process operating in natural populations is, therefore, called natural selection.
• The process of natural selection, acting on variability inherent in the population, over millions of years, has given rise to the great diversity we see in the biological world.
• Ancestry of different breeds can be traced to wild rock pigeon (artificial selection).
• Man has been using a similar process for improving the qualities of domesticated plants and animals for centuries.

• Plant-breeding and animal-breeding are very similar to the action of natural selection, the difference being that the role of nature is played by man.
• The criteria for selection are based on human interests

• To obtain cows with high milk yield, the dairy scientists monitor milk production of a large number of cows.
• Only the calves produced by cows that are high-yielders are chosen to breed and form the next generation.
• When this process is repeated (i.e., artificial selection is applied) for many generations, a population of cows with high milk yield is obtained.
• Here, the task of selection is done by man.

Speciation And Isolation

• Speciation is the formation of one or more new species from an existing species.
• The crucial episode in the origin of species occurs when the gene pool of a population is severed from other populations of the parent species and gene flow no longer occurs.
• Speciation can take place in two modes based on the geographical relationship of the new species to its ancestral species.
• When a population, formerly continuous in range, splits into two or more geographically isolated populations and forms new species, the mode of speciation is called allopatric speciation.
  This can happen by subdivision of the original population when a geographical barrier such as a creeping glacier, a land bridge (e.g., Isthmus of Panama), an ocean, or a mountain cuts across a species range.
  Alternatively, a small number of individuals may colonize a new habitat which is geographically separated from the original range.
  Darwin’s finches that formed separate species in the Galapagos Islands and the Australian marsupials that radiated to form new species are its examples.
• In the second speciation mode, a subpopulation becomes reproductively isolated in the midst of its parent population; this is sympatric speciation. So, sympatric speciation is the formation of species within a single population without geographical isolation.
  The usually quoted example of sympatric speciation comes from polyploidy-the multiplication of the normal chromosome number.
  This can happen when chromosomes fail to segregate at meiosis or replicate without undergoing mitosis.

Species Concept

• Species is the basic unit of classification.
• The term was coined by John Ray (1693).
• Most taxonomists define species as morphologically distinct and reproductively isolated natural population or group of populations where individuals resemble one another more closely than the members of other species; have a similar anatomy, karyotype, and bio- chemicals; interbreed freely; and form a genetically closed system. There are three basic concepts about species.
  • Morphospecies concept
    • It is the earliest concept of species.
    • Davis and Heywood (1963) have defined it as the assemblage of individuals with morpho- logical features in common, and separable from other such assemblages by correlated morphological discontinuities in a number of features.
    • However, the number of morphological characters chosen for separating species varies from taxonomist to taxonomist.
    • “Lumpers” combine all populations with broadly similar traits into a single species while “splitters” separate various populations with even minor morphological differences into distinct species.
  • Biological species concept
    • Though first proposed by Buffon (1753), biological species concept was formulated by Mayr (1942).
    • According to it, a biospecies (biological species, biological species concept) is a sexually interbreeding or potentially interbreeding group of individuals which is reproductively isolated from other species and is, therefore, separated from others by the absence of genetic exchange.
    • Normally, species are distinct from one an- other by both morphological traits and reproductive isolation.
    • However, sibling species are those distinct species which are almost identical morphologically but are distinct from each other due to the absence of interbreeding, e.g., Drosophila pseudoobscura and D. persimilis.
    • Biological species concept is, therefore, mainly based on the absence of cross-fertilization between the members of two species.
    • Cross-fertilization tests carried out by taxonomists on the individuals of morphologically and geographically separated populations have resulted in the revision of species and the grouping of many of them into single species, e.g., several species of North American sparrows as subspecies and the races of a single song sparrow, Passarella melodia.
    • The only problem in using reproductive isolation is the absence of sexual reproduction in several organisms-prokaryotes, some protists, some fungi, and some plants (e.g., commercial banana) and animals.
    • Further, cross-fertilization experiments cannot be performed on such a large number of species that occurs in varied geographical areas.
    • Reproductive isolation cannot be used as a criterion in case of fossils.
    • Living organisms and fossils can be grouped only on the basis of their morphology and biochemistry.
    • Mayr (1987) has named morphologically grouped asexual species as paraspecies while Ghiselin (1987) has named them pseudospecies.
  • Evolutionary species concept
    • All evolutionary taxonomists have been in search of a proper definition of species which is the basic unit of classification.
    • One such definition has been given by Simpson.
    • According to Simpson (1961), “an evolutionary species is a lineage (an ancestor-descendent sequence of population) evolving separately from others and with its own unitary evolutionary role and tendencies.”
    • The concept stresses on evolutionary isolation with sexual isolation being its one aspect.
    • It is more dependent on differences, which can be morphological, genetic, behavioral, and ecological, to know evolutionary distance.
    • However, evolution does not occur simultaneously in all traits.
    • Neither its rate nor direction (in which it is occurring) are the same.
    • Reproductive isolation may be defined as the existence of intrinsic barrier to the in- terbreeding in natural populations. Each of these intrinsic barriers is called a reproductive isolating mechanism. According to Mayr (1942), reproductive isolating mechanisms are the biological properties of individuals which prevent the interbreeding of naturally sympatric populations.
    • Reproductive isolation in the form of hybrid sterility is known since long. In the labora- tory or in zoos, hybrids can be produced between species that do not interbreed in na- ture. Horses and donkeys are two different species; a hybrid, mule, is produced from the mating of a male donkey and a mare (female horse).
    • Similarly, mating between stallion (male horse) and female donkey results in a hybrid called hinny.
    • Both mule and hinny are sterile.
    • There are examples of species that can produce fertile hybrids in captivity. You might have heard about the famous “tigon”-a hybrid of African lioness (Panthera leo) and Asian tigers (Panthera tigris)-which is fertile. No barrier to hybridization between these species has evolved during their long isolation from each other. Natural selection has not favored a reduction in hybridization for the simple reason that no hybridization has been possible. Other examples of species that breed in captivity and produce fertile hybrids are the mallard (a duck) and the pintail duck, the polar bear and the Alaskan brown bear, and the platy and swordtail fish. But these species do not interbreed at all in natural condition.

Modern Synthetic Theory Of Evolution

• Evolution on the grand scale of geological time is called macroevolution.
• Evolution at the genetic level is called microevolution.
• Studies of how individual traits evolve within natural populations provide powerful evidence that natural selection can be a powerful agent of microevolutionary change within species. The progressive change in allele frequencies within the population is microevolution.
• The unit of evolution is population.
• The unit of natural selection is individual.
• The modern synthetic theory of evolution is the result of the work of a number of scientists, namely T. Dobzhansky, R.A. Fisher, J.B.S. Haldane, Sewall Wright, and Stebbins.
• The synthetic theory includes the following factors:
  • Gene mutations
  • Changes in chromosome structure and number
  • Genetic recombination
  • Natural selection
  • Reproductive isolation
  • Migration
  • Hybridization

Neutral Theory Of Evolution

• According to Kimura, most of the mutations are neutral and are not eliminated from the population.
• This is against natural selection.
• Kimura proposed that speciation is not due to the selection of advantageous genotypes but due to the elimination of deleterious alleles and random selection of neutral alleles.
• It emphasized that most mutations are of neutral value and genetic drift is responsible for divergence.
• It means that all mutations are alike in adaptive value. It is only chance or random drift which delineates a novel collection of mutants into a group divergent from the parental population.

Place of Humans in the Animal Kingdom

• Today human evolution is being studied due to the following reasons:
  • There is homology in the chromosomes of man and great apes. The banding patterns of human chromosomes number 3 and 6 are compared with those of particular autosomes in the chimpanzee. It shows a common origin for man and chimpanzee.
  • Today, besides autosomal chromosomes, V-chromosomes and mitochondrial DNA are being studied, as they are uniparental in origin and do not take part in recombination.
  • Evidence from blood proteins: It has been proved by the blood protein tests that man is the most closely related to great apes (chimpanzee and gorilla).
  • Evidence from blood groups: Blood groups A and B are found in apes and not in monkeys.
  • Evidence from hemoglobin: There is 99% homology in the hemoglobin of man and gorilla.
• Human beings are vertebrates and belong to class Mammalia.
• Mammals evolved from primitive reptiles in early Tri- assic period, about 210 million years ago.
• But for nearly 150 million years, mammals existed as relatively inconspicuous group of small rat-like creatures, completely dominated by the large number of gigantic reptiles of the Mesozoic age.
• It is only after the great extinction of dinosaurs and other large reptiles that mammals diversified and began to occupy earth’s many different habitats.
• Within class Mammalia, human beings belong to order Primate a group that originated about 65 mya and includes not only monkeys and apes but also lorises, lemurs, and tarsiers.
• Anthropoid apes, or the ancestors of monkeys, apes, and humans, evolved about 36 mya; and hominids, or the ancestors of apes and humans, evolved about 24 mya.
• Today, apes are represented by two families, namely, Pongidae (which includes chimpanzees, gorillas, and orangutans) and Hylobatidae (which includes gibbons).
• Chimpanzee and gorilla are restricted to Africa whereas orangutans and gibbons are found only in Asia.
• Humans belong to the family Hominidae in which Homo sapiens is the only living species.

Early Human Ancestors

• Tracing the evolution of human beings, both by fossil hunting and molecular methods, is one of the most exciting and active areas of research in biology.
• The fossil evidence cleatly indicated that genera such as Ramapithecus and Sivapithecus were the forerunners of hominids.
• A genus called Australopithecus appeared in Africa about 5 mya and ultimately gave rise to Homo about 2 mya.
• But even Australopithecus had a brain measuring only about 350-450 cm3.

• The most important change that must have occurred during the three million years or so between the appearance of Australopithecus and that of our genus must, therefore, have been a phenomenal increase in brain size, all the way up to 1400-1450 cm3-a characteristic of our species.
• A combination of molecular data and a modern interpretation of the fossil record suggests that gibbons probably diverged from the main line of hominid evolution about 10 mya, that the orangutan did so about 8 mya, and the ancestors of gorilla and chimpanzee, about 4 mya.
• Gorilla and chimpanzee separated from each other only 2.3 mya.

Place and Sequence of Human Evolution

• There is evidence that almost all of hominid evolution occurred in Africa and Asia and that the evolution of human species took place in Africa.
• Several species belonging to genus Homo can be rec- ognized from the fossil record. For example, Homo habilis lived in Africa about 2 mya and had a larger brain than Australopithecus; it used tools and was bipedal.
• Another species, Homo erectus, appeared about 1.7 mya, used fire, and is believed to have migrated to Asia and Europe.
• The fossils of the so called “Java man” and “Peking man” belong to Homo erectus. It was replaced by Homo sapiens.
• A primitive form of Homo sapiens, called Neanderthal man (Homo sapiens neanderthalensis), was common in Europe and Asia.
• Neanderthal men resembled us, though they were rela- tively short and stocky and more powerfully built.
• Neanderthals made tools and used animal hides as clothing.
• They built hut-like structures for dwelling and buried their dead.
• There is evidence that an abrupt transition occurred all over Europe whereby the Neanderthal man was wiped out. It gave way to the more efficient cousin the Cro- Magnon-about 34,000 years ago.
• The Cro-Magnon people left behind very elaborate cave paintings showing the attainment of a form of culture not unlike our own.
• After the last glacial period (about 10,000 years ago), modern Homo sapiens sapiens began to spread all over the globe. They cultivated plants, domesticated animals, and reached enormous population sizes.
• Homo sapiens appeared in Africa about 5,00,000 years ago and probably replaced Homo erectus there.
• But in Asia, Homo erectus appears to have survived for another 2,50,000 years when it was finally replaced by Homo sapiens migrating from Africa.

Human Evolution

Place or Origin of Man

• It has been established that Dryopithecus is one of the oldest fossil which in turn evolved into apes and man.
• The origin and evolution of man can be studied in the following three major headings: prior to ape man, ape-man including prehistoric man, and true man including the living modern man.

Prior to Ape Man

• Dryopithecus discovery
  • The fossil of Oryopithecus africanus was discovered from the Miocene rocks of Africa and Eu- горе.
  • It lived about 15 mya.
  • Dryopithecus and Ramapithecus were hairy and walked like gorillas and chimpanzees.
  • Ramapithecus was more man-like while Dryo-pithecus was more ape-like.
  • Dryopithecus is the direct ancestor of modern-day apes.
    Characteristics
    • It was ape-like, but had arms and legs of the same length.
    • Heels in its feet indicate its semi-erect pos- ture.
    • It had large brain, a large muzzle, and large canines.
    • It was without brow ridges.
    • It was arboreal, knuckle-walker, and ate soft fruits and leaves.
    • Oryopithecus africanus is regarded a com- mon ancestor of man and apes (gibbons, or- angutan, chimpanzee, and gorilla).
    • It is also called proconsul.
• Proconsul discovery
  • Proconsul africanus or o. africanus was discovered by Louis S.B. Leakey in 1948 from the rocks around Lake Victoria of Kenya, Africa.
  • It lived in early Miocene epoch.
    Characteristics
    • It was morphologically intermediate between apes and man in many features.
    • It had rounded man-like forehead and long, pointed, ape-like canines.
    • It moved on land on all the four limbs and, hence, is not considered amongst the direct ancestors of man.
    • Proconsul gave rise to the ancestors of chimpanzee and gorilla in the Pliocene, about 4 mya.
    • Chimpanzee and gorilla diverged from each other only about 2.3 mya, in Pleistocene epoch.
• Sivapithecus discovery
  • This fossil was discovered from the middle and late Pliocene rocks of Shivalik Hills of India. Hence, it is named Sivapithecus.
    Characteristics
    • It was like Dryopithecus.
    • Its forelimbs, skull, and brain were like those of monkeys, while the face, jaws, and teeth resembled those of apes.
• Ramapithecus discovery
• It has been established that in late Miocene epoch, Oryopithecus gave rise to Ramapithecus (Rama- the hero of Indian legend, pithecus-ape), which was on the direct line of human evolution.
• Ramapithecus survived from late Miocene to Pliocene.
• Thus, he appeared about 14-15 mya.
• The fossil of Ramapithecus was discovered by Edward Lewis (1932) from the Pliocene rocks of Shivalik Hills of India.
• Kenyapithecus wickeri was discovered by L.S.B. Leakey (1962) from the Pliocene rocks of Kenya (Africa).
• It was similar to Ramapithecus. But Ramapithecus was older than Kenyapithecus.

Ape-Man Including Prehistoric Man

• Australopithecus (first ape-man) discovery
  • The early human stock gave rise to Australopithecus.

• • It is the connecting link between apes and man.
  • Raymond Dart (1924), a South African anthropologist, discovered the fossil of Australopithecus africanus (African ape-man) from Pliocene rocks near Tuang in Africa.
  • A. africanus appeared about 5 mya.
  • Actually, the skull discovered by Dart was of a 5-6 year old baby. So, it is also called the Tuang baby.
  • Some fossils of A. africanus were also discovered from Pleistocene epoch.
  • Two mya, australopithecines probably lived in East African grasslands.
  • Evidence shows that they hunted with stone weapons but essentially ate fruits.
    Characteristics
    • Australopithecus africanus was about 1.5 m high and had human as well as ape characters.
    • It had bipedal style of locomotion, ate om- nivorous diet, and had erect posture.
    • It had human-like teeth, but had more of an ape brain than a human brain.
    • Its brain capacity was about 500 cc-similar to that of an ape.
    • He lived in caves.
    • Brow ridges projected over the eyes.
    • It did not have chin.
    • There was lumbar curve in the vertebral col- umn.
    • The pelvis was broad. Australopithecus afri- canus existed until about 1.5 mya and gave rise to Homo habilis about 2 mya.
    • Australopithecus africanus also gave rise to man-like apes called Australopithecus robus- tus and Australopithecus boisei along a sep- arate line that ended blindly. (They did not give rise to any other creatures.)
    • In 1981, Donald Johanson found a 3.2 mil- lion years old skeleton of a female human ancestor.
    • He nicknamed it Lucy.
    • Lucy’s scientific name is Australopithecus afarensis.
    • Six species of Australopithecus are known.
    • These are A. africanus (African ape-man and southern ape or Taung baby), A. afarensis (Lucy), A. ramidus, A. aethiopicus, A. robus- tus, and A. boisei. So we can say that Austra- lopithecus had two main types.
      • Gracile type: Australopithecus afarensis (Johanson) was represented by fossil Lucy with small brain, small molar teeth, pelvic girdles, and short fingers like humans.
      • Robust type: A. robustus (also originally called Paranthropus) had heavier body structure, massive check tooth, and cranial capacity of 600 cm2.
        (Other examples are Zinjanthropus/A. boisei of R. Leakey, Africa; and Megan- thropus from Java.)
• Homo habilis (able or skillful man, the toolmaker, or “handy man”) discovery
  • Louis S.B. Leakey and his wife Mary Leakey (1960) discovered the fossils of Homo habilis from the Pleistocene rocks of Olduvai Gorge in East Africa.
  • He lived in Africa about 2 mya.
  • The first human-like being-the hominid-was H. habilis. He probably did not eat meat.
    Characteristics
    • He was about 1.2-1.5 m tall.
    • He had bipedal locomotion and moved erect.
    • He had about 650-800 cc cranial capacity.
    • Teeth were like that of modern man. e. Homo habilis (habilis-mentally able or skillful) was the first toolmaker and used tools of chipped stones extensively.
    • He is also called handy man because heaps of tools found with these fossils included sharpened stones which indicate that Homo habilis was capable of “making tools.”
    • He also led community life in caves and greatly cared for the young ones.
• Homo erectus (erect man)
  • Homo erectus appeared about 1.5 million years ago, in middle Pleistocene.

• • He probably ate meat.
  • He is called middle Pleistocene man. H. erectus evolved from H. habilis.
  • He was about 1.5-1.8 m tall.
  • H. erectus males were probably larger than fe- males.
  • He had erect posture.
  • His skull was flatter than that of modern man.
  • He had protruding jaws, projecting brow ridges, small canines, and large molar teeth.
  • The cranial capacity was 900 cc.
  • Cranium was domed to accommodate the large brain.
  • He was omnivorous.
  • He made more elaborate tools of stones and bones, hunted big game animals, and perhaps knew the use of fire.
  • H. erectus includes three fossils: Java ape-man, Peking man, and Heidelberg man.
    • Java ape-man Discovery
      • In 1891, Eugene Dubois discovered a fossil from Pleistocene rocks in Central Java (Island of Indonesia).
      • He named it as Pithecanthropus erectus.
      • Pithecanthropus means “ape-man.”
      • Mayer, in 1950, named it as Homo erectus erectus.
        Characteristics
        • Body was 1.65-1.75 m tall and weight was about 70 kg.
        • Legs were long and erect, but body was slightly bent when moving.
        • Chin was inconspicuous and nose was somewhat broader.
        • Forehead was low and receding, but brow ridges were high, like those of apes.
        • Skull cap was thick and heavy and flat- tened in front.
        • Cranial capacity was 800-1000 cc (aver- age 950 cc).
        • Lower jaw was large and heavy.
        • Teeth were large, but quite like those of modem man, except larger canines of the lower jaw.
        • Lips were thick and protruding.
        • He was omnivorous and cannibal.
        • Perhaps, he was the first prehistoric man to make use of fire for hunting, defense, and cooking.
    • Peking man discovery
      • W.C. Pei (1924) discovered the fossils of Peking man from the limestone caves of Choukoutein near Peking (Beijing-capital of China was formerly known as Peking) and named them Sinanthropus.
      • Davidson Black (1927) named it Sinan- thropus pekinensis.
      • Mayer (1950) renamed it as Homo erec- tus pekinensis (a subspecies).
      • The Pleistocene rocks from which the fossils of the Peking man were excavated are about 6 lakh years old.
        Characteristics
        • Placing Java ape-man and Peking man as subspecies of H. erectus has a sound basis, because of close similarities between the two.
        • The body structure was quite similar in both.
        • Being about 1.55-1.60 m tall, the Pe- king man was slightly shorter and a little lighter and weaker.
        • The only noticeable difference of the Pe- king man from the Java ape-man was its large cranial capacity, which ranged from 850 cc to 1100 cc.
        • Like Java ape-man, the Peking man was omnivorous and cannibal.
        • There is a clear evidence of the use of fire by him.
        • It has been confirmed that both Java and Peking men used to live in caves in small groups or tribes.
        • The tools of Peking man were relatively more sophisticated.
  • Heidelberg man discovery
    • In 1908, one of the most perfect fossil jaw belonging to middle Pleistocene was found by workmen working near Heidelberg, Germany.
    • It was shown to Otto Schoetensack, who gets the credit for its discovery. It was named Homo erectus heidelbergensis.
      Characteristics
      • He had lower jaw with all the teeth.
      • Teeth were human-like.
      • The massive jaw was apelike.
      • He used tools and fire.
      • Cranial capacity is believed to be about 1300 cc, which is intermediate between that of erect man (H. erectus) and Neanderthal man (H. sapiens neanderthalensis).
      • Thus, it is regarded as intermediate between pithecanthropines and Neanderthals.

True Man Including the Living Modern Man

• Neanderthal man (Homo sapiens neanderthalensis) discovery
  • The fossils of Neanderthal man were first obtained from Neanderthal Valley in Germany in the late Pleistocene epoch by C. Fuhlrott (1856).
  • Later, many other fossils were excavated in various countries by different palaeontologists.

• • Characteristics
    • He had slightly prognathous face.
    • Neanderthal man walked upright, as we do, and had low brows, receding jaw, and high domed head.
    • If there was anything truly different about him, it was that he was much stockier than we are.
    • Cranial capacity was 1300-1600 cc.
    • Neanderthal man existed half-a-million years ago, but was most numerous from about 100,000 years ago.
    • He became extinct 30,000 years ago.
    • Neanderthal man was the legendary cave dweller, having heavy brow ridge and humped back.
    • He was adapted to a cold environment and encountered a succession of glaciers that passed over most of the northern temperate regions of the world.
    • He was not only a skilled hunter but also a true predator-a specialization that did not happen among hominids before or after him.
    • Neanderthal man was cannibal and fashioned the skin into clothing to protect himself against the harsh climate.
    • Natural caves became camp-sites that were illuminated and heated by fire.
    • It is believed that he buried his dead with flowers and tools. He may have had a religion.
    • It is usually considered that Homo sapiens neanderthalensis did not evolve into Homo sapiens.
• Cro-Magnon man (Homo sapiens fossilis) discovery
  • He has been known as Cro-Magnon man because his fossils were first discovered in 1868 from the Cro-Magnon rocks of France by MacGregor.
  • Cro-Magnon man emerged about 34,000 years ago in Holocene epoch.
  • Thus, he is regarded as the most recent ancestor of today’s man.
    Characteristics
    • The Cro-Magnon man had, like us, about 1.8 m tall, well-built body.
    • His face was perfectly orthognathous with a narrow, elevated nose; broad and arched forehead; moderate brow ridges; strong jaws with man-like dentition; and a well-developed chin.
    • His cranial capacity was, however, somewhat more than ours, being about 1650 cc.
    • It is, therefore, believed that the Cro-Magnon man was somewhat more intelligent and cultured than the man of today.
    • He could walk and run faster and lived with families in caves.
    • He made excellent tools and even orna- ments-not only of stones and bones, but also of elephant tusks.
    • His tools included spears, bows, and arrows, as he was omnivorous.
    • The use of skin clothes by this man is also confirmed.
    • A number of cave paintings done by the Cro- Magnon man have been discovered.
    • He was the direct ancestor of the living modern man.
    • Prehistoric cave art developed about 18,000 years ago.
• Living modern man (Homo sapiens sapiens) discovery
  • Further evolution of man after the Cro-Magnon man involves the evolution of culture rather than that of anatomy.
  • Homo sapiens sapiens appeared about 25,000 years ago in Holocene epoch and started spreading all over the world about 10,000 years ago.
  • Agriculture came around 10,000 years ago and human settlements started.

Modern Humans

Homo sapiens

• The evolutionary journey to modern humans ends with the appearance, about five hundred thousand years ago, of Homo sapiens (wise man), i.e., our own species.
• We are newcomers to the human family-H. sapiens has not been around nearly as long as H. erectus was.
• Still humans have changed quite a bit since those early days.

Homology in Chromosomes of Man and Great Apes

• The somatic cells of humans contain 46 chromosomes (44 autosomes and 2 sex-chromosomes).
• Human chromosomes are usually obtained by cultur- ing certain types of white blood cells from the peripheral blood.
• They can then be treated with specific stains to produce characteristic bands along the length of each chromosome.
• The pattern of banding so obtained is unique for each pair of chromosomes.
• Banding techniques enable the identification of individual chromosomes and their parts.
• The diploid number of chromosomes in gorilla, chimpanzee, and orangutan is 48.
• Comparisons have been made between banded chromosomes of man and those of the great apes.
• The total amounts of DNA in human diploid cells and great apes are not dissimilar.
• But what is most interesting from an evolutionary viewpoint is that the banding pattern of individual human chromosomes is very similar and, in some in- stances, identical to the banding pattern of apparently homologous chromosomes in the great apes.
• Diagrammatic representations of the banding pattern of human chromosome numbers 3 and 6 are compared with those of particular autosomes in chimpanzee.
• This remarkable similarity in the fine structural organization of chromosomes is understandable only in terms of a common origin of man and chimpanzee.

Some Important Points

• Mars has CO2 and water vapors and is supposed to have life. CO2 is present in traces. It has no green-house effect. Hence, it is very cold and does not support life. Mercury and moon do not have any sign of life due to the absence of water vapors. This extra terrestrial origin of life was visualized by Hoyle and Wickramasinghe.
• Darwin used the term “warm little pond” for early hot sea, rich in biomolecules. This primitive sea was alkaline.
• K. Bahadur exposed ammonia, formaldehyde, and ferrous chloride to strong sunlight and obtained a mixture of amino acids called Jivam.
• Variation in behavior: Cicada insect has a life span of 17 years. It emerges from soil, remains alive for 5 weeks, and then dies after mating and laying eggs. Dolphins can imitate and laugh. Bat can detect small insects of size (0.0a mm). Male Baya (weaver bird) of India builds its elaborate nest and decorates it with colorful petals to attract female Baya.
• Multiformity among organisms: Internal differentiation increases with the progress in evolution. Human beings are one of the most recently evolved animals. They show the following features:
  • The total length of blood vessels in our body is 96,000 km.
  • The fastest nerve impulse travels at the rate of 532 km/h.
  • The internal area of our lungs is 93-100 m2 which is 40 times the external surface area of our body.
  • Human brain has 10,000 million nerve cells.
  • We have more body hair than apes but shorter and softer.
  • O, disappears from the atmosphere at 16 km height.
  • We remain blind for 30 min/day by blinking our eyes.
  • Bones are as strong as concrete and as hard as granite but far lighter than both.
    We retain only 18% of what we learnt yesterday.
• Synapsid reptiles were mammal-like reptiles that gave rise to mammals. They had a single temporal fossa on the lateral side of skull and heterodont teeth. They originated in Permian period. They are extinct.
• In 1858, Dr. P.L. Sclater divided, for the first time, the earth into six regions (realms) according to the distribution of birds. Later on, Alfred Russel Wallace (1876) classified the earth into six regions (realms) for all ani- mals and plants.
• In all animals, early development is similar, i.e., passing through morula → blastula→ gastrula stages, showing their common origin.
• Early embryos of all vertebrates show basic similarity in having somites, tail, gill clefts, notochord, etc. These traits can be explained as the characters of evolution.
• Any vertebrate organ also passes through different stages during development. For example, mammalian heart is initially two-chambered, then it becomes three-chambered, and then becomes four-chambered. The development of all triploblastic animals starts from zygote and undergoes similar changes to form gastrula having three primary germ layers (ectoderm, mesoderm, and endoderm) which have same fate in organogenesis. Early embryos of different vertebrates resemble in possessing similar structures such as gill slits, notochord, and tail. Not only this, but in the course of development, at different stages, an embryo looks like the embryo of different phyla forms which the given organism has evolved.
• It can be explained on the basis of recapitulation theory (von Baer)/biogenetic law (Haeckel) which states that ontogeny (developmental history of an individual) repeats phylogeny (developmental history of race).
• Types of fossils
  • Macrofossils: These are larger than 1 cm in size.
  • Unusual fossils: These form by sudden preservation of entire organism, e.g., Solnhofen limestone quarry of Southern Germany containing fossils of Archaeopteryx.
  • Gastroliths: These are found in abundance in the body cavities of certain reptiles.
  • Molds and casts: The material surrounding the fossil hardens and preserves the outer details. The actual bodies disintegrate and are removed by slippage of the ground leaving hardened cavities called molds. When molds are filled with natu- ral deposits, they are called casts, e.g., fossils of Pompeii city buried in the volcanic ash of Mount Vesuvius in 79 AD.
• Preservation in ice: In the woolly mammoths from Siberia, the flesh is so well preserved that it can be fed to dogs. It was discovered from Lena Delta in 1790 and Siberia in 1901.
• Fossils in petroleum springs and asphalts: These were found in Rancho La Brea now in Los Angeles.
• Fossils in resins and ambers: Fossil flies in amber from the Baltic forests of Europe during Oligocene period.
• The process of fossilization to preserve finer details is known as histometabasis.
• Mummies: The bodies of dead animals or plants become dehydrated in deserts and are preserved as mummies.
• T. Dobzhansky wrote the book “Genetics and Origin of species.”
• Darlington wrote the book “The Evolution of Genetic Systems.”
• Darwin wrote “Descent of Man and Selection in Relation of Sex” in which he put forward his theory of evolution of man from ape-like ancestors.
• Law of superposition: The lower stratum of geological formation was the first to be deposited and is the oldest.
• Willston’s rule: During the evolution of lineage, serially homolog parts tend to reduce in number but get more and more differentiated, e.g., prawn’s leg.
• Allometry: The study of differential growth rate was called allometry.
• Missing links: Fossils that act as transition between two present-day groups of organisms are called missing links. For example, Archaeopteryx-a fossil of crow-sized toothed bird-acts as a link between reptiles and birds.
• Empedocales (493-435 BC) is regarded as the father of the concept of evolution.
• Seymouria (extinct reptile) is a connecting link between Amphibia and Reptilia.
• Lycaenops (extinct reptile) is a connecting link between reptiles and mammals.
• Wallace’s line: In 1863, A.R. Wallace drew an imaginary dividing line on the map between the Oriental and Australian realms (regions). This line is known as Wallace’s line.
• Sibling species: Species that morphologically look similar but are reproductively isolated are called sibling species.
• Living fossils: A living fossil is a living animal of ancient origin with many primitive characters. A living fossil has been living as such from the time of origin without many changes.
• Eugenics: It is the branch of science that deals with the improvement of human race genetically. It can also be divided into two types: Negative eugenics and positive eugenics. Under negative eugenics, people with inferior and undesirable (dysgenic) traits are prevented from reproducing.

• Homo sapiens or modern man is a member of order Primate, sub-order Anthropoidea. Primates are supposed to have evolved from primitive, tiny, insect-eating quadruped, similar to modern tree shrews, which lived between 75-60 mya during Eocene period. These belong to order Insectivora. Two evolutionary lines diverged leading to present-day prosimians (treeshrews, lemurs, lorises, and tarsier) and the Anthropoidea (including old-world and new-world monkey, ape, and man).
• The first (ape+man) ancestor originated in Oligocene period 30-35 mya under the name Propliopithecus. (Its fossils were found in the Fayum deposits of Egypt.) It is represented by fossil jaws and teeth. Aegyptopithecus is contemporary of Propliopithecus (Kahira).
• Dryopithecus: The Oligocene ancestor gave rise to the Miocene group of (apes + man) called Dryopithecus (formerly known as Proconsul). It lived in Africa and Asia. It had semi-erect posture with hindlimbs and forelimbs of the same size. Hands and skull were monkey like, forehead was human-like, and jaws and dentition were ape-like. Sivapithecus, discovered by ChopraSimon team, is another fossil ape from the Shivalik Hills in India (derived from Dryopithecian stock).
• An aberrant branch from Oreopithecus evolved in late Miocene early Pliocene, Oreopithecus, which later on became extinct. Ramapithecus (Kenyapithecus) originated 1415 mya; it had a few teeth and fragments of jaw. It is believed to have evolved from Dryopithecus in Shivalik Hills in India during late Miocene and early Pliocene.
• Grimaldi: From the caves in village Grimaldi on the Mediterranean coast, cranial capacity 1655 cc is believed to have given rise to Negroid stock.
• Chancelade: In rock shelter near Chancelade in Dordogne France, cranial capacity 1450 cc gave rise to modern Eskimos.
• Modern man: H. sapiens sapiens evolved about 25,000 years ago but spread to various parts of the world about 10,000-11,000 years ago. There is thinning of skull bones, slight reduction in cranial capac- ity (1400-1450 cm3), four flexors in vertebral column, and slight rising of skull cap. Modern man underwent cultural evolution:
  • Paleolithic (age of tools of stones and bones and cave paintings),
  • Mesolithic (age of animal husbandry, development of language, reading, and writing),
  • Neolithic (development of agriculture, manufacture of pottery, and clothes),
  • Bronze Age, and
  • Iron Age.
• Forgery of Piltdown man (Eoanthropus dawsoni): Charles Dawson in 1921 reconstructed the skull from the cranium of modern man and the lower jaw of ape. The fossil skull is known as Piltdown, after the English hamlet where it was found.
• Cranial capacities

• Transitional forms connecting Home erectus with Homo sapiens have been uncovered from Europe. These are Steinheim skull (Germany), Swanscombe skull (second interglacial period), Fontechvade skulls (France, third interglacial period), and Ehringsdorf skull. All of these are called early H. sapiens. The course of evolution of man started in Africa.

 

Assertion – Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: Interspecific hybrids are usually sterile.

Reason: Interspecific hybrids receive chromosomes from two different species.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 2. Assertion: Magnolias, tulips, and Sassafras are found in Eastern United States and Eastern China only.

Reason: These are examples of restricted distribution.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 3. Assertion: Cretaceous period is called age of dinosaurs.

Reason: Fishes originated in Devonian period.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 4. Assertion: Theory of special creation attributes the origin of life to a vitalistic event.

Reason: According to this theory, the God is creator of life.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 5. Assertion: Both mule and hinny are sterile.

Reason: These are the examples of hybrid sterility.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 6. Assertion: The earliest organisms were anaerobes, having arisen in a sea of organic molecules, and were chemoheterotrophs.

Reason: Before the supply of organic molecules exhausted, some of the heterotrophs might have evolved into autotrophs.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 7. Assertion: There are chances of breakdown of isolating mechanism in allopatric speciation.

Reason: Allopatric speciation is rapid process of speciation.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 8. Assertion: Balanced polymorphism is directly related with directional selection.

Reason: Directional selection favors the maximum dominacy of characters.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 9. Assertion: Artificial selection is highly beneficial for humans.

Reason: Artificial selection is carried out by man.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 10. Assertion: Batesian mimicry is a form of mimicry in which an edible species resembles an inedible one.

Reason: Batesian mimicry is a form of protective mimicry.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 11. Assertion: There is no life on moon.

Reason: Water is absent on moon.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 12. Assertion: The first living organisms on earth were autotrophs.

Reason: They were capable of performing chemosynthesis.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 13. Assertion: Base analogs induced transition.

Reason: Base analogs perform forbidden pairing.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 14. Assertion: Sympatric species are geographically isolated.

Reason: Sympatric species are reproductively isolated.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 15. Assertion: Somatic mutations are sometimes inheritable.

Reason: Some organisms show vegetative propagation.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 16. Assertion: Plants having odd number of sets of chromosomes are fertile.

Reason: Plants having even number of sets of chromosomes are sterile.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 17. Assertion: Colchicine induces polyploidy.

Reason: Colchicine causes disjunction of chromosomes.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 18. Assertion: Change in structure of chromosome is called chromosomal aberration.

Reason: Substitution is an example of chromosomal aberration.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 19. Assertion: The first life originated in water.

Reason: Conditions were favorable for the origin of life in water.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 20. Assertion: A single mutation may produce a new species.

Reason: Mutation may cause major variation in genetic material and these are inheritable.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 21. Assertion: Evolution is not occurring at present.

Reason: Evolution takes a very long time to occur.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 22. Assertion: Analogous organs show common ancestry.

Reason: Analogous organs show evolution.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 23. Assertion: Lung fish is a connective link between fishes and amphibia.

Reason: Lung fishes show characters of both fishes and amphibia.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 24. Assertion: Bird’s embryo shows tooth buds for some time.

Reason: Ontogeny repeats phylogeny.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 25. Assertion: Liger in a hybrid animal.

Reason: Liger is fertile.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Human Health And Disease

Health

• The term “health” is very frequently used by everybody. How do we define it?
• Health does not simply mean absence of disease or physical fitness.
• It can be defined as a state of complete physical, mental, and social well-being.
• When people are healthy, they are more efficient at work.
• This increases productivity and brings economic pros- perity.
• Health also increases longevity of people and reduces infant and maternal mortality.
• Balanced diet, personal hygiene, and regular exercise are very important to maintain good health.
• Yoga has been practiced since time immemorial to achieve physical and mental health.
• Awareness about diseases and their effect on different bodily functions, vaccination (immunization) against infectious diseases, proper disposal of wastes, control of vectors, and maintenance of hygienic food and water resources are necessary for achieving good health.

Disease

• When the functioning of one or more organs or systems of the body is adversely affected, characterized by various signs and symptoms, we say that we are not healthy, i.e., we have a disease.
• Diseases can be broadly grouped into infectious and non-infectious.
• Diseases that are easily transmitted from one person to another are called infectious diseases.
• Infectious diseases are very common and each one of us suffers from these at some time or the other.
• Some infectious diseases such as AIDS (acquired immuno deficiency syndrome) are fatal.
• Among non-infectious diseases, cancer is the major cause of death.
• Drug and alcohol abuse also affect our health adversely.
• Disease can be defined as a disorder of the mind or body.
• This term covers varied conditions leading to the deviation of human body from the normal course or deviation from the normal health.
• Thus, disease is opposed to health.
• Since time immemorial, diseases have been a prime concern of man.
• Early man thought that diseases were caused by evil spirits. Hence, cure consisted of pacifying the evil spirits with the help of charms and magic.
• Hippocrates (460-359 BC), the great Greek physician, was the first to separate medicine from religion and superstition.
• He gave the description of disease symptoms and emphasized the need for good diet, fresh air, and rest.
• He also described that human body has a natural tendency to defend itself against diseases.
• Pathogen: It is an organism which is capable of producing a disease.
• The ability of the pathogen to gain entrance and produce symptoms of disease is called pathogenicity.
• Virulence is the degree of pathogenicity of a pathogen in the host body.
• Pathogens are biological agents including bacteria, fungi, viruses, mycoplasma, protozoans, helminths, etc.
• A parasite is an organism that lives at the expense of the other organism, called host, for obtaining food and shelter.
• A parasite may cause disease in the host.
• Infection is the interaction between the host and the parasite having a competition for superiority.
• Disease occurs when the parasitic organism is able to win.
• Infection or transmission may occur by contact; through air, food, water, and insect bite; or by contaminated materials.
• Researches in parasitology described the causative organisms (parasites) of diseases.
• Our knowledge of human parasites developed after the invention of microscope in 1835.

Read and Learn More NEET Biology Notes

Categories of Diseases

• Diseases can be broadly divided into two groups: congenital and acquired.
  • Congenital diseases: These occur since birth and. may result from metabolic disorder or defect in development.
  • Acquired diseases: These develop after birth and can be further divided into two main categories:
    • Communicable diseases: These rapidly spread from one person to another, e.g., infectious diseases.
    • Non-communicable diseases: These do not spread from person to person. These include all other acquired diseases.

Communicable Diseases

• The infectious diseases rapidly spreading from person to person are called communicable diseases.
• Communicable diseases can be categorized on the basis of different aspects.
• On the basis of transmission, these may be divided into the following categories:
  • Transmitted through air
  • Transmitted through food and water
  • Transmitted through insect bite
  • Transmitted by contact
• On the basis of causative organism or pathogen, these diseases may be categorized into the following categories:
  • Bacterial
  • Viral
  • Protozoic
  • Helminthic
  • Fungal diseases

Diseases Caused By Viruses

• Common cold
  • Common cold is one of the most infectious human ailments.
  • It is caused by rhinoviruses.
  • They infect the nose and respiratory passage but not the lungs.
  • Common cold is characterized by nasal congestion and discharge, sore throat, cough, headache, tiredness, hoarseness, etc., for 3 to 7 days.
• Influenza
  • It is commonly known as “flu” and is highly infectious.
  • It causes fever and pain all over the body and affects the nose, throat, and air passages as in common cold.
  • The disease is caused by various types of influenza viruses (e.g., Myxovirus influenzae).
  • It is characterized by with fever, headache, sore throat, cold with sneezing, and pain all over the body with restlessness.
  • In neglected cases, complications such as pneumonia, bronchitis, and ear infections may develop.
  • There is no vaccine at present which can give protection against all types of influenza viruses as each epidemic is of a different type.
• Smallpox (variola)
  • It is a highly infectious disease starting with high fever, chill, backache, and headache, followed by the appearance of rash on the third day of illness.
  • The rash appears first on the face and then on the rest of the body (periphery to center).
  • It is more on the face and limbs and less on the trunk.
  • It starts as small reddish spots which change into papules.
  • These in turn change into small vesicles containing clear fluid.
  • Vesicles change into pustules.
  • Finally, a scab is formed and it falls off by the third week.
  • These scabs leave deep pits or scars known as pock marks.
  • Many children become blind and develop discharge from the ear.
  • This disease is caused by a smallpox virus named variola virus (dsDNA virus).
  • The virus is present in the oral and nasal dis- charge of the patient and is ejected during the acts of coughing, sneezing, fomites, etc. It infects healthy people.
  • Vaccination against smallpox is one of the best preventive remedies available today.
  • This was discovered by Edward Jenner in 1798.
  • Smallpox has been eradicated from India.
• Chicken pox (varicella)
  • It is a mild but highly infectious disease causing slight fever and a rash which undergoes changes in vesicles, pustules, and, finally, a dark brown scab which falls off leaving no scar unlike small-pox.

• • The rash comes out in crops. With each fresh crop, there may be slight fever again.
  • The rash first appears on the trunk. There are more lesions on the trunk than on the face and limbs.
  • The disease is caused by a virus of chicken pox named varicella-zoster which is passed out in the discharges of the respiratory tract of an infected person directly as droplets or through contaminated articles used by him.
  • Vaccination against chicken pox is now available.
  • The most common late complication of chicken pox is shingles caused by the reactivation of varicella-zoster.
• Measles (rubeola disease)
  • Measles is a highly infectious disease causing fever, inflammation of the air passages, and a rash all over the body.
  • It especially attacks children below the age of 5 years; those who have escaped may be attacked even in the later life.
  • It is caused by rubeola virus (RNA virus) which is passed out in the secretions of nose and throat of the infected person as droplets or in articles soiled by these secretions.
  • The disease starts with the catarrh of nose and throat, and fever.
  • The eyes become red and watery, and the face becomes flushed.
  • Rash which is slightly pinkish in color appears first on the back of the ear and face, and then spreads downwards on the body.
• Mumps (infectious parotitis)
  • It is an infectious disease causing fever, difficulty in opening the mouth, and painful swelling of the parotid glands which lie just below the lobe of the ears.
  • It is caused by paramyxovirus (RNA virus), which comes out in the saliva of the infected person.
  • The patient should take complete bed rest till the swelling subsides in order to avoid complications.

• • Usually, there are no complications. But in some cases, there may be pain and swelling of the testes (orchitis) or pain in the abdomen.
• Poliomyelitis
  • This disease was called infantile paralysis.
  • But it is now known that the disease may occur at any age.
  • This disease spreads mainly through intestinal discharges.
  • It may also spread through contaminated food or drink and by flies or other insects that may contaminate food or drink.
  • Polio virus (ssRNA) usually enters the body via alimentary canal where it multiplies and reaches the nervous system (spinal cord) through the bloodstream.
  • Its incubation period is 7-14 days.
  • It produces inflammation of the nervous system.
  • The earliest sign of this disease is the involvement of central nervous system causing inability to bend the head forward.
  • Stiffness of the neck is an important sign. Paralysis starts following the weakness of particular skeletal muscles.
  • The attack of paralysis begins with high fever, headache, chills, and pain all over the body.
  • If the muscles of larynx and pharynx are involved, it proves fatal.
  • Within 2-3 days, the paralysis reaches its maximum.
  • There is no sure cure for polio.
  • The patient should be kept isolated.
  • He should be given complete rest.
  • An adequate arrangement for the proper disposal of urine and feces of the patient must be provided because these contain polio virus.
  • Overcrowding of children in schools, playgrounds, and cinemas should be avoided.
  • Polio is preventable. Polio vaccine is safe and effective.
  • Now-a-days, multiple vaccines are used against polio, diphtheria, whooping cough, and tetanus simultaneously.
• Trachoma
  • It is caused by Chlamydia trachomatis.
  • Trachoma is a chronic inflammatory disease of the eye affecting the conjunctiva and cornea.
  • It is characterized by the development of granules. Its common symptoms are inflammation, pain, and watering of the eye.
  • It can lead to blindness.
  • Infection spreads by direct contact and by the use of handkerchiefs, towels, and pillows of the patient.
• Rabies (hydrophobia):
  • It is caused by Rhabdovirus.
  • It is introduced in the body by the bite of rabid (mad) dogs usually.
  • It can be injected by the bite of jackels, wolves, cats, etc. Incubation period is from 10 days to 1 year.
  • Fear of water is the most important characteristic symptom of this disease.
  • Other symptoms are saliva from the mouth, severe headache, high fever, alternating periods of excitement and depression, and inability to swallow even fluids due to choked throat.
  • The virus destroys the brain and spinal cord. Rabies is 100% fatal.
  • There should be compulsory immunization of dogs and cat population.
• Dengue fever
  • Dengue fever is caused by an RNA containing arbovirus (arthropod borne virus) of Flavivirus group which also causes yellow fever (not found in India).
  • Thus, the virus that causes dengue fever is a mosquito borne flaviribo virus.
  • The virus of dengue fever is transmitted by the bite of female Aedes aegypti (mosquito).
  • Incubation period is 3-8 days.
  • These fevers are of two types: classical dengue fever and dengue hemorrhagic fever.
  • The symptoms of classical dengue fever are as follows:
    • Abrupt onset of high fever.
    • Severe frontal headache.
    • Pain behind the eyes which worsens with eye movement.
    • Muscles and joint pain.
    • Loss of sense of taste and appetite.
    • Measles-like rash over chest and upper limbs.
    • Nausea and vomiting.
  • The symptoms of dengue hemorrhagic fever are similar to those of classical dengue fever except the following:
    • Bleeding from nose, mouth, and gums, and skin bruising.
    • Severe and continuous stomach pains.
    • Frequent vomiting with or without blood.
    • Pale cold or clammy skin.
    • Excessive thirst (dry mouth).
    • Rapid weak pulse.
    • Difficulty in breathing.
    • Restlessness and constant crying.
  • If there is fever, consult the doctor at once; take Paracetamol tablets on the advice of doctor.
  • Do not take Aspirin and Disprin.
  • Do cold sponging if fever is high.
  • Give plenty of liquids to the patient.
  • Rush the patient to the hospital if there is bleeding from any part of the body or if the patient be- comes unconscious.
  • No vaccine for dengue fever is available.
  • Eliminate mosquito breeding places by covering small water containers and water tanks, and changing the water of cooler every week-where Aedes mosquitoes breed.
  • Wear clothes that cover arms and legs.
  • Do not allow children to play in shorts and half-sleeved clothes.
  • Use mosquito repellents and repellent cream, and sleep in mosquito-net.
• Chikungunya
  • It is caused by Chikungunya virus.
  • This virus was first isolated from human patients and Aedes aegypti mosquitoes from Tanzania in 1952.
  • The name “Chikungunya” is derived from the native word for the disease in which patient walks “doubled up” due to severe joint pain.
  • Its symptons include sudden onset of fever, crippling joint pain, lymphadenopathy, and conjuctivitis.
  • Some show hemorrhagic manifestations.
  • No vaccine is available.

Diseases Caused By Bacteria

• Cholera
  • This is an acute infectious disease caused by Vibrio cholerae.
  • These may get into a healthy person with contaminated food and water.
  • The patient starts passing stools frequently, which are white like rice water, and gets repeated vomiting.
  • Since a large quantity of fluid and salts are rapidly lost through stools and vomit, the most important dose treatment is to replace the lost fluid and salts equally rapidly.
  • Rapid replacement of fluid and elecrolytes is done by oral rehydration therapy.
• Typhoid
  • It is an infectious disease caused by Gram-negative bacterium called Salmonella typhi which is a non-spore forming bacillus.
  • Typhoid germs are contracted from food or drink contaminated with excreta from carriers or patients.
  • The spread is facilitated by poor environmental hygiene. Immunity following the infection is not sufficient to prevent relapse.
  • A large number of organisms have to be ingested by a healthy person to suffer from typhoid.
  • Smaller number may produce the disease if the organism is very virulent or if the resistance of the host is poor.
  • The acid in stomach destroys Salmonella that is ingested. Hence, patients having achlorhydria (no acid in stomach) or who take large amounts of antacids to neutralize the acid in stomach suffer more often from typhoid.
  • The normal intestinal flora produces short-chain fatty acids which are lethal to Salmonella.
  • When this is reduced by antibiotics, the patient is more prone to typhoid.
  • Salmonella that causes enterocolitis after ingestion invades the mucosal cells and multiplies within them.
  • These bacteria do not penetrate beyond lamina propria and multiply in the lymphoid tissues (Peyer’s patches) of the small intestine.
  • Inflammatory changes occur with the accumulation of leucocytes.
  • Enterotoxin liberated by the bacteria may form abscess which may burst causing ovoid ulcers. This may cause hemorrhage. If the ulcer reaches the serosa, perforation occurs leading to peritoni- tis.
  • The infection is usually localized in the small in- testine and colon.
  • The incubation period is usually 12-72 h but may be up to 2 weeks.
  • Nausea, vomiting, and an early chill are common initially followed by colicky abdominal pain and diarrhoea of watery, green, offensive stools.
  • Blood mixed with stool and high fever may occur if there is involvement of colon.
  • Symptoms may subside within a week or two.
  • There is clinical syndrome characterized by fever, headache, cough, splenomegaly, and leucopenia.
  • This is called enteric fever.
  • The fever is continuous and rises in a step-wise manner.
  • Diagnosis is done by the Widal test which determines the agglutinins against the antigen.
  • The test is usually positive in the second week of the disease.
  • The concentration of agglutinins must keep on rising with time to suggest the disease.
  • The treatment involves the use of antibiotics, antipyretics, and rest. TAB vaccine is useful against typhoid.
  • Special care must be taken to ensure that persons who are engaged as cooks or work in eating establishments are not “carriers” of this disease (who can keep spreading this disease through food).

• Diphtheria
  • This disease is caused by Corynebacterium diphtheriae usually affecting children up to 5 years of age.
  • It may start as sore throat, chills with mild fever, and, sometimes, vomiting and headache.
  • Throat and/or tonsils show a gray membrane which may spread down and cause hoarseness and difficulty in breathing.
  • Nose may be affected giving rise to a blood-tinged nasal discharge from one nostril.
  • If the disease is not treated early and properly, the toxin produced by the germs affects the heart and the nervous system, and proves fatal.
  • The most important preventive measure against this disease is that all babies should be immunized within the first six weeks of birth using DPT vaccine.
• Whooping cough (pertussis)
  • It is a highly infectious disease of young children causing inflammation of the respiratory passage with severe attacks of cough.
  • It is caused by Bordetella pertussis, which comes out while coughing from the discharges of the nose and throat of the patient.
  • It spreads by the direct inhalation of droplets from the patient or the carrier or by the articles freshly soiled by the discharges.
  • The cough becomes troublesome, especially at night.
  • The face becomes red during coughing.
  • These repeated bouts of violent cough end in a whoop.
  • Whooping sound is produced due to rushing in of air during deep inspiration at the end of a bout of cough.
  • The child usually vomits and there is frothy discharge from his mouth and nose.
  • The disease can be prevented by immunizing all infants with whooping cough vaccine which is available singly or in combination as triple vaccine (i.e., DPT).
• Pneumonia
  • This disease is caused by Diplococcus pneumoniae.
  • Pneumonia is a serious disease of lungs.
  • Lymph and mucus collect in the alveoli and bronchioles of lungs so that lungs do not get sufficient air.
  • Therefore, proper exchange of gases does not take place in the alveoli.
  • It usually lowers the resistance of the body.
  • Infection spreads by the sputum of the patient.
  • Breathing rate increases with high-grade fever. It is common in children below the age of 5 years.
• Tetanus (lockjaw)
  • It is caused by Clostridium tetani.
  • The first indications of this disease are irritability and restlessness; the neck becomes stiff and there is difficulty in chewing and swallowing.
  • Subsequently, spasms of muscles of the jaw and face take place and, thus, “lockjaw” occurs.
  • There is severe pain.
  • It is often a fatal disease.
  • The toxin mainly affects “voluntary muscles.”
  • Tetanus organisms live in the intestines of horses and other animals without doing any harm. The spores are, therefore, abundant in the soil manufactured with animal dung.
  • Spores may survive for 60 years or more in contaminated soil.
  • On entering the body by way of wounds, the spores release active bacteria.
  • The latter multiply and secrete powerful exotoxin into the tissue and blood.
  • The exotoxin known as tetanospasmin brings about tetanus.
  • Anti-tetanus serum (ATS) injection should be ad- ministered in case of an injury.
• Plague
  • This disease is characterized by high fever and a bubo (painful swelling) in the groin or the armpit.
  • Plague is caused by Yersinia pestis-a deadly bacterium.
  • It is primarily a disease of rodents but it accidently affects man.
  • It gets transmitted from rat to rat through the rat fleas.
  • But when a rat dies of plague, the fleas leave the dead rat; if any man is around, they bite him and accidently inject some plague germs into his blood.
  • In its typical form, bubonic plague is not transmitted from one man to another, but always from a rat to one or more men.
• Tuberculosis (TB)
  • It is also called Koch’s disease.
  • It is caused by Mycobacterium tuberculosis.
  • The bacteria damage the tissues and release a toxin named tuberculin which produces the disease.
  • It affects the lungs, lymph nodes, bones, and joints.
  • Incubation period is quite variable.
  • The symptoms of pulmonary (lungs) tuberculosis are fever, cough, blood-containing sputum, pain in the chest, loss of weight, excessive fatigue, failure of appetite, rise of temperature in the evening, hoarseness of throat, night sweating, and rapid pulse.
  • BCG vaccine gives considerable protection against tuberculosis.
• Leprosy (Hansen’s disease)
  • This disease is caused by Mycobacterium leprae, which was discovered by Hansen.
  • The symptoms of leprosy include the appearance of light-colored patches on the skin, thickening of nerves, and partial or total loss of sensation in the affected parts of the body.
  • These are accompanied by fever, pain, ulcers, and skin eruptions.
  • Deformities of toes and fingers may also develop.
  • The bacilli leave the body in nasal discharge from the throat during coughing, sneezing, and even speaking, and through broken skin lesions. The patient is treated with DDS (diamino diphenyl sulfone).

Disease Spread By Protozoa

• Malaria
  • Of all the communicable diseases caused by protozoa, malaria is the most destructive for man. Malaria is widespread in the tropics and subtropics and also in certain areas of temperate zones.
  • It was earlier thought to be caused by foul gases emanating from marshes. Hence, the disease was named malaria (Italian, mala-bad, aria-air).
  • The term malaria was given by Maculoch (1837).
  • A French army doctor, Charles Laveran (1880), discovered malaria parasite (Plasmodium vivax and P. malariae) in the RBC of malaria patient.
  • Stephens discovered P. ovale and Welch discovered P. falciparum. Lancisi suspected that malaria occurs where mosquitoes are found.
  • Richard Pfeiffer (1892) explained that some blood-sucking insects are involved in the transmission of malaria.
  • Scottish doctor, Patrick Manson (1894) suggested that mosquito has some role in the transmission of malaria.
  • A doctor in Indian Army, Sir Ronald Ross (1897) established relationship between mosquito and malaria.
  • On August 29, 1897, Ronald Ross discovered the oocysts of Plasmodium on the stomach of female Anopheles mosquito.
  • Hence, August 29 is observed as the Mosquito Day.
  • For his valuable discovery, Ronald Ross was awarded the Noble Prize of Medicine in 1902.
  • The life history of malaria parasite in female Anopheles mosquito was studied by B. Grassi (1917).
  • A. Bignami and G. Bastianelli.
  • Erythrocytic schizogony in the RBC of man was studied by Golgi (1885).
  • E. Shortt (1948) reported the development of malaria parasite in the liver of man.
  • The detailed monograph of malarial parasites was written in 1996 by P. C. C. Garnham. Their fine structure has been reviewed by M. Rudzinska (1969).
  • Malaria is a common tropical disease caused by protozoa Plasmodium through the bite of female Anopheles mosquito.
  • There are mainly four types of Plasmodium infec- tions causing malaria:
    • Plasmodium falciparum (malignant tertian malaria)
    • Plasmodium vivax (benign tertian malaria)
    • Plasmodium malariae (quartan malaria)
    • Plasmodium ovale (mild tertian malaria)
  • When an infected mosquito bites an individual, its saliva, rich in parasites (sporozoites), is injected.
  • The sporozoites enter the circulation and then the liver (pre-erythrocytic phase).
  • It multiplies in the liver cells forming merozoites.
  • After 5-9 days, the merozoites enter the red blood cells (erythrocytic phase) forming trophozoites which subsequently mature to become schizonts.
  • Erythrocytic merozoites are discharged into the bloodstream when the red blood cells degenerate.
  • This results in an attack of malarial fever.
  • The red blood cells are destroyed by the spleen which enlarges, and some of the merozoites continue to develop in the liver (exo-erythrocytic phase) causing a relapse.
  • This phase is absent in the life cycle of P. falciparum.
  • Some of the merozoites, for unknown reasons, do not form schizonts but develop into male and female gametocytes.

• • During mosquito bite, these gametocytes are ingested.
  • They fertilize in mosquito’s stomach and develop into sporozoites which localize in the salivary glands of the mosquito.
  • These sporozoites enter the human bloodstream on a subsequent mosquito bite and, thus, complete the cycle.
  • The onset may be insidious with abdominal pain, nausea, dry cough, and malaise. Rarely it may be acute and with fever and chills.
  • In the early stage, fever may be persistent for several days. But soon it develops into a synchronous periodicity.
  • A classical attack of fever has a chill, rise in temperature to 40-41°C, headache, and myalgia.
  • This is followed by several hours of profuse sweating and fall in temperature.
  • In vivax and ovale malaria, these paroxysms occur every 48 h (benign tertian) whereas in malariae, these occur every 72 h (quartan).
  • In falciparum malaria, the temperature is usually persistently elevated or may progress to 48-hour cycle (malignant tertian malaria).
  • These cycles may be repeated in case of benign tertian malaria due to exo-erythrocytic phase.
  • Liver is moderately enlarged and tender. Spleen is often palpable in acute attack. It is soft to firm and occasionally tender.
  • Rarely jaundice may occur.
  • Malarial parasites may be visible on the peripheral smear examination.
  • Malarial parasites can also be demonstrated on bone marrow examination and by splenic puncture.
  • The treatment of malaria includes drugs such as Daraprim, Chloroquine, and Quinine (derived from the bark of Cinchona tree).
• Amoebiasis
  • Amoebiasis is caused to man by protozoan Entamoeba histolytica.
  • It is also known as amoebic dysentery. Entamoeba histolytica was first discovered by Lambl (1859).
  • Friedrich Lösch, a Russian zoologist, in 1875, re- discovered this protozoan in the feces and intesti- nal ulcers of dysentery patients and succeeded in transferring it to puppies.
  • Entamoeba histolytica is a microscopic endopara- site of man and is commonly found harboring the lumen of the upper part of large intestine, i.c., the colon.
  • It invades the mucosa and sub-mucosa of the intestinal wall and causes amoebic dysentery or amoebiasis.
  • The trophozoites of the parasite make their way deep by eating through the mucosa of the intestinal wall.
  • Here they multiply by binary fission and spread rapidly outward to form flask-shaped ulcers containing cellular debris, lymphocytes, blood corpuscles, and bacteria.
  • This causes the formation of abscesses in the intestinal wall.
  • Penetration into the sub-mucosa by trophozoites is made possible by histolysis as well as cytolysis.
  • The mechanism involves the dissolution and necrosis of tissues and cells by a proteolytic enzyme of the nature of histolysin secreted by trophozoites themselves.
  • As the sub-mucosa is eroded by the trophozoites, the ulcers burst and the blood capillaries rupture.
  • The blood and ulcer contents pour into the lumen of the intestine and pass outside with stool.
  • This characterizes the amoebic dysentery or amoebiasis.
  • The stool of a dysenteric person is usually acidic and consists of swarms of Entamoebae as well. Person suffering from amoebic dysentery has repeated blood-mixed, slimy, foul-smelling motions.
  • Sometimes, the trophozoites make their way through blood circulation into the brain, liver, spleen, lungs, and gonads.
  • Here also they destroy the tissues and cause the formation of abscesses (cavities containing pus).
  • Within the liver, the trophozoites cause severe lesion affecting the metabolic activities.
  • The formation of abscesses in brain usually proves fatal.
  • It mainly occurs by the ingestion of tetra-nucleated cysts in food or drinks.
  • Diagnosis consists of microscopical detection of trophozoites or cysts in fecal smears.
  • The presence of white, stone-shaped “Charcot- Leyden” crystals in feces suggests E. histolytica infection.
  • The treatment of amoebic dysentery is not very difficult, but permanent cure is sometimes hard to achieve as relapses do occur.
  • For temporary relief, an alkaloid called Emetine is effective.
  • A synthetic derivative called Dehydroemetine is equally effective.
  • The most significant advancement in the treatment of amoebiasis has been the use of Metronidazole and Tinidazole as amoebicides.
  • It is very active against both intestinal and extraintestinal amoebiasis.
  • The prevention of infection is entirely a matter of hygiene, both personal as well as municipal.
• Giardiasis (diarrhea)
  • It is also known as “backpacker’s disease” because the travelers are most vulnerable to this disease.
  • It is caused by a zooflagellate protozoan named Giardia intestinalis.
  • It is the first human parasitic protozoan known. It lives in the upper parts (duodenum and jeju- num) of human small intestine.
  • It is found all over the world.
  • The parasites perch over the living cells of intestinal wall by means of their adhesive discs.
  • They absorb nourishment from the food passing through intestine, and grow and multiply through binary fission.
  • The large number of parasites interfere with di- gestion and absorption of food.
  • This causes epigastric pain, abdominal discom- fort, diarrhea, headache, and, sometimes, fever.
  • The disease caused by Giardia is popularly known as giardiasis or diarrhea (watery and frequent stools).

Diseases Caused By Helminthes

• Ascariasis
  • It is caused by Ascaris lumbricoides which is cosmopolitan in distribution.
  • It is an endoparasite of the small intestine of human beings, but also infects pigs and cattle.
  • It is more common in children because they generally have the habit of eating soil and clay, which may be infected by the eggs of Ascaris.
  • The food of the worm consists of semi-digested food of the host, the blood, and the fluid of the alimentary canal of the host.
  • The worm ingests food with the help of suctorial pharynx.
  • There is no secondary host in the life cycle of this parasite.
  • Since a large number of adult Ascaris worms normally infest a single host, they obstruct the intestinal passage and, thereby, cause abdominal discomforts such as colic pains.
  • The patient may also suffer from impaired digestion, diarrhea, and vomiting.
  • In children, where the Ascaris infection is quite common, mental efficiency is affected and body growth is retarded.
  • The disease can best be treated by administering antihelminthic drugs such as oil of chenopodium, Alcopar, Bendex, Dewormis, and Zental.
  • Since the main source of infection is the pollution of soil, water, and vegetables, utmost care should be taken in the dispersal of human fecal matter.
  • Vegetables, as a rule, should be washed properly before eating.
  • Parents should see to it that their children do not take to the habit of eating soil.
• Filariasis
  • Wuchereria (W. bancrofti and W. malayi), the filarial worms, cause a slowly-developing chronic inflammation of the organs in which they live for many years, usually the lymphatic vessels of lower limbs. The disease is called elephantiasis or filariasis.

• • The genital organs are also often affected, resulting in gross deformities.
  • The pathogens are transmitted to a healthy person through the bite of female Culex mosquito vectors.

Disease Caused By Fungi

• Dermatophytes are a group of closely related fungi.
• These infect the skin, hair, and nails and cause a variety of clinical conditions collectively called as dermatophytoses or tinea or ringworm.
• Dermatophytes include three genera:
  • Trichophyton: It infects skin, hair, and nails.
  • Microsporum: It attacks hair and skin but, usually, not the nails.
  • Epidermophyton: It infects skin and nails, but not the hair.
• Thus, the main symptoms of the disease are the appearance of dry, scaly lesions on various parts of the body such as skin, nails, and scalp.
• These lesions are accompanied by intense itching.
• In tinea cruris or dhobie itch, the groin and perineum are involved.
• In tinea barbae, the bearded areas of the face and neck are involved.
• Tinea pedis or athlete’s foot is the ringworm of the foot and tinea capitis is the ringworm of the scalp.
• Heat and moisture help these fungi to grow in the skin folds such as those in the groin or between the toes.
• The infection of ringworm is usually acquired from soil or by using towels, clothes, or combs of infected persons.

Immunity

• Everyday we are exposed to a large number of infectious agents.
• However, only a few of these exposures result in disease. Why?
• This is due to the fact that the body is able to defend itself from most of these foreign agents.
• This overall ability of the host to fight the disease causing organisms conferred by the immune system is called immunity.
• The organs of the immune system include primary lymphoid organs such as bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes and secondary lymphoid organs such as lymph nodes and spleen which provide sites of interaction of lymphocytes, and antigens.

Lymphoid Organs

Lymphoid organs are those organs where the maturation and proliferation of lymphocytes take place.

Types of Lymphoid Organs

Lymphoid organs are of two types:

• Primary lymphoid organs (central lymphoid organs)
  • These are those organs where T-lymphocytes and B-lymphocytes mature and acquire their antigen- specific receptors.
  • Thymus and bursa of Fabricius of birds are primary lymphoid organs.
  • The bone marrow of mammals is considered equivalent to the avian bursa of Fabricius.
  • All cells of the immune system are initially derived from the bone marrow.
  • They form through a process called hematopoiesis.
  • During hematopoiesis, the bone marrow-derived stem cells differentiate either into mature cells of the immune system or into precursors of cells that migrate out of the bone marrow to continue their maturation elsewhere.
  • Bone marrow produces B-cells, NK cells, granulocytes, and immature thymocytes, in addition to red blood cells (RBCs) and platelets.
  • Thymus is also called the “throne of immunity” or the “training school of T-lymphocytes.”
  • Its function is to produce mature T-cells.
  • Immature thymocytes/prothymocytes leave the bone marrow and migrate into the thymus.
  • Through a remarkable maturation process, sometimes referred to as thymic education, T-cells that are beneficial to the immune system are spread while those T-cells that might evoke a detrimental auto-immune response are eliminated.
  • Mature T-cells are then released into the blood-stream.
• Secondary lymphoid organs (peripheral lymphoid organs)
  • After maturation, B-lymphocytes and T-lymphocytes migrate blood via vascular and lymphatic systems to the secondary lymphoid organs where they undergo proliferation and differentiation.
  • Secondary lymphoid organs are lymph nodes, spleen, tonsils, Peyer’s patches of the small intestine, appendix, and mucosal associated lymphoid tissue (MALT).
  • MALT is located within the lining of major tracts (digestive, respiratory, and urinogenital).
  • It constitutes about 50% of the lymphoid tissue in human body.
  • In secondary lymphoid organs such as lymph nodes and spleen, there are two types of areas:
    • Thymus-dependent area: It is any part of peripheral lymphoid organs populated by T-lymphocytes, e.g., paracortex of lymph nodes and center of Malpighian corpuscle of spleen.
    • Thymus-independent area: It is rich in B-lymphocytes.

Spleen

• Spleen is an immunologic filter of the blood.
• It contains B-cells, T-cells, macrophages, NK-cells, and RBCs.
• In addition to capturing foreign materials (antigens) from the blood that passes through spleen, migratory macrophages bring antigens to the spleen via blood- stream.
• An immune response is initiated when the macrophages present the antigen to the appropriate B- or T-cells.
• This organ can be thought of as an immunological conference center.
• In the spleen, B-cells become activated and produce large amounts of antibody.
• Also, old RBCs are destroyed in the spleen.

Lymph Nodes

• Lymph nodes function as an immunologic filter for the body fluid known as lymph.
• Lymph nodes are found throughout the body.
• Composed mostly of T-cells, B-cells, and macrophages, the nodes drain fluid from most of our tis- sues.
• Antigens are filtered out of the lymph in the lymph node before returning the lymph to circulation.
• In a similar fashion as the spleen, the macrophages that capture antigens present these foreign materials to T- and B-cells, consequently, initiating an immune response.
• The lymphoid tissue located within the lining of major tracts (respiratory, digestive, etc.) is called MALT.

Types of Immunity

There are two types of immunities against pathogens: Non-specific innate immunity and specific acquired immunity.

Non-specific innate immunity

It includes all those defense elements with which an individual is born, i.e., always available to protect a living body. It can be further of four categories:

• Anatomic barriers or physical barriers
  • Skin
    • Skin is the physical barrier of body.
    • Its outer tough layer, stratum corneum, prevents the entry of bacteria and viruses.
  • Mucous membrane
    • Mucus secreted by mucous membrane traps the microorganisms and immobilizes them.
    • Microorganisms and dust particles can enter the respiratory tract with air during breathing; these are trapped in the mucus. The cilia sweep the mucus loaded with microorganisms and dust particles into the pharynx (throat).
    • From the pharynx, it is thrown out or swallowed for elimination with the feces.
    • Mucous membrane over the mucosa of stomach protects it from the corrosive action of HCI.
• Physiological barrier
  • Oil secreted by the oil glands and sweat secreted by the sweat glands make the surface of the skin acidic (pH 3-5). This does not allow microorganisms to establish on the skin. Some friendly bacteria also occur on the skin, which release acids and other metabolic wastes that check the growth of pathogens. Sweat also contains an enzyme named lysozyme that destroys the cell walls of many bacteria.
  • Lysozyme is also present in tears and checks eye infections.
  • It is also present in the saliva which kills bacteria present in food.
  • Highly acidic gastric juice also kills harmful bacteria in the stomach.
  • Bile checks the growth of foreign bacteria in the intesting.
  • The mesh of fine hair in our nostrils filters out particles which may carry pathogens. Nasal secretions also destroy the harmful foreign germs with their lysozyme.
  • Certain bacteria normally live in vagina. These bacteria produce lactic acid. Lactic acid kills the foreign bacteria.
  • Interferon:
    • These are glycoproteins released by the cells in response to a viral infection. which they help to combat.
    • These interferons do not kill/inactivate the virus, but make the unattacked cells less susceptible so that they are prevented from the attack of virus.
    • Interferons were discovered by Isaac and Lindemann.
    • They also prevent the virus from taking over the cellular machinery.
    • Interferon proteins have proved to be effective in treating influenza and hepatitis, but their role in cancer treatment is doubtful. (Interferons are now included in cytokine barrier.)
• Phagocytic barrier
  The internal defense is carried on by white blood corpuscles (WBCs), macrophages, inflammatory reaction, and fever.
  • WBCs (leucocytes)
    • Leucocytes in general and lymphocytes in particular are capable of squeezing out through the wall of blood capillaries into extravascular regions.
    • This phenomenon is called diapedesis.
    • Leucocytes protect in different ways.
      • Lymphocytes: These can produce plasma cells which secrete antibodies to provide immunity.
      • Monocytes: These are phagocytic in action.
      • Eosinophils: These can attach themselves to parasitic forms (mostly in case of helminths) and cause their destruction by liberating lysosomal enzymes on their surface.
      • Neutrophils: These eat up harmful germs and are, therefore, phagocytic in nature.
  • Macrophages
    Macrophages are formed by the enlargement of monocytes. These are large cells which are phagocytic in nature.
• Inflammatory barrier:
  • When microorganisms such as bacteria and viruses enter the body tissue through some injury, these produce some toxic substances which kill more cells.
  • These broken cells also release some material which attracts the mast cells.
  • The mast cells release histamine.
  • Histamine causes the dilation of capillaries and small blood vessels surrounding the injury and increases the permeability of capillary walls.
  • More blood flows to the area making it red and warm.
  • The fluid (plasma) leaks out into the tissue spaces, causing its swelling.
  • This reaction of body is known as inflammatory response.
  • The plasma that accumulates at the injured site dilutes the toxins secreted by bacteria and decreases their effect.
  • Fever
    • The inflammatory response may be in the region of the wound (localized) or it may be spread all over the body (systemic). o In systemic inflammatory response, the number of WBCs increases. Generally, the fever is caused by the toxins released by pathogens or by compounds called py- rogens (fever-producing substances).
    • These compounds are released by WBC in order to regulate the temperature of the body.
    • Moderate fever stimulates the phagocytes and inhibits the growth of microorganism.
    • However, a very high fever is dangerous. o It is necessary to bring down fever by giving antipyretics (fever-reducing drug) and by applying cold packs.
    • Thus, interferons, leucocytes, macrophages, inflammatory response, and fever form the second line of defense.
• NK cells
  • NK cells are another population of large granular lymphocytes which destroys a wide variety of infectious microbes and certain spontaneously arising tumor cells.
  • Unlike T-cell, these do not mature in the thymus and unlike both B- and T-cells, these lack surface molecules/antigen receptors. NK cells are present in the spleen, lymph nodes, red bone marrow, and blood.
  • These cells release g-interferon which stimulates their cytolytic activity.
  • These may release chemical-perforins which cause the cytolysis of the microbe or may bind to a target cell to inflict damage by direct contact.
  • NK cells probably attack cells that do not display major histocompatibility complex (MHC) antigens.
  • NK cells are defective or decrease in number in some cancer patients and in patients with AIDS.
• Complement system
  • A complement system is a set of 30 different protein molecules always found in the blood.
  • There are no cells in the system.
  • With an infection, this system of molecules is activated, leading to a sequence of events on the surface of the pathogen that helps destroy the pathogen and eliminate the infection. A complement system can be activated in two main ways.
  • The first and most potent way, known as classical pathway, occurs when IgG (or IgM) binds to the antigen at the surface of a cell. This exposes the Fc region of the antibody such that the first complement protein (C1) binds.
  • The second means of activation, known as alternate pathway, is a part of the natural (in- nate) immune response (i.e., neither antibodies nor T-cell receptors are involved). Here, certain polysaccharides found on the surface of bacteria activate the system.
  • This can occur immediately and does not require prior exposure to the molecules.
  • But in either case, a cascade of events follows, in which each step leads to the next.
  • At the center of the cascade are steps in which the proteolysis of a complement protein leads to a smaller protein and a peptide.
  • The smaller protein remains bound to the complex at the surface of the microorganism while the peptide diffuses away.
  • As a result, the membrane loses all its regulatory properties; that is to say, the cell swells and bursts.
  • This final complex of molecules that causes cell lysis is termed as the membrane attack complex (MAC).
  • Thus, the complement system triggers a constellation of effects that help in dealing with an infection.
    • Opsonization
    • Chemotaxis (attracting macrophages and neutrophils)
    • Inflammation
    • Lysis (rupturing membranes of foreign cells)
  • Innate immunity is a non-specific type of defense that is present at the time of birth. This is accomplished by providing different types of barriers to the entry of foreign agents into our body. Innate immunity consists of the following four types of barriers.
    • Physical barriers: The skin on our body is the main barrier which prevents the entry of microorganisms. Mucus coating of the epithelium lining the respiratory, gastrointestinal, and urogenital tracts also help in trapping the microbes entering our body.
    • Physiological barriers: Acid in the stomach, saliva in the mouth, tears from eyes all prevent microbial growth.
    • Cellular barriers: Certain types of leukocytes (WBC) of our body [such as polymorphonuclear leukocytes (PMNL-neutrophils) and monocytes] and natural killer (type of lymphocytes) in the blood as well as macrophages in tissues can phagocytose and destroy microbes.
    • Cytokine barriers: Virus-infected cells secrete glycoproteins called interferons which protect non-infected cells from viral infection.

Acquired or adaptive or specific immunity

• Immune system forms the third line of defense.
• There are two components of immune system in body: Humoral immune system and cellmediated immune system. The important characteristics of immune systems are as follows:
  • Specificity: Ability to differentiate between foreign molecules.
  • Diversity: To recognize enormous variety of foreign molecules.
  • Discrimination: Ability to differentiate between foreign and self, i.e., will respond to foreign compound and avoid response to self molecules.
  • Memory: After encountering any foreign agent or microbe, immune response is evoked. It results in the formation of memory cells responsible for retaining memory. This is the basis of vaccination as the second response to the same microbe will evoke hightened immune response due to memory cells.
• Specific immunity involves two types of cells: Lymphocytes and antigen presenting cells.
  • Lymphocytes
    • Lymphocytes (a type of WBCs) are the main cells of immune system of the body.
    • Lymphocytes, meant for immune system, are of two types: T-cells and B-cells.
    • Both types of cells develop from the stem cells found in the liver of the fetus and in the bone marrow cells of the adult.
    • The lymphocytes that migrate to the thymus and differentiate under its influence are called T-cells while the cells that continue to be in the bone marrow for differentiation are called B-cells.
    • Final maturation of young lymphocytes occurs in lymphoid tissues such as lymph nodes, spleen, and tonsils.
    • T-cells are responsible for cellular immunity. However, B-lymphocytes produce antibodies that take part in humoral immunity.
    • Both T-cells and B-cells require antigens to trigger them into action but they respond differently.
    • B-lymphocytes are independent of thymus and, in man, probably complete their early maturation within the bone marrow.
    • These are called B-cells because these mature within the bursa of Fabricius found in the cloaca of birds.
  • Antigen presenting cells
    • Antigen presenting cells (APCs) are a special class of cells which process and present exogenous antigens.
    • APCs include macrophages, B-cells, and dendritic cells.
    • APCs are strategically located in places where antigens are likely to penetrate non-specific defenses and enter the body.
    • These are the epidermis and dermis of the skin and the mucus membranes that line the respiratory, urinary, and reproductive tracts.
    • The steps in processing and presenting an exogenous antigen by an APC include the following:
      • Ingestion of antigen
      • Digestion of antigen into peptide fragments
      • Fusion of peptide fragments to MHC and its insertion into the plasma membrane. This triggers either a cell mediated immune response or a humoral mediated immune response.

Antigens

• Antigens are foreign molecules that invade the body of an organism.
• The word “antigen” is a shortened form of “antibody generating” as they stimulate the production of anti-bodies in response to infection.
• Antigens are generally large molecules.
• The majority of them are made of proteins or polysaccharides found on the cell walls of bacteria and other cells or on the coats of viruses.
• All antigens are not the parts of microorganism.
• Other structures such as pollen grains, white of an egg, shell fish, certain fruits and vegetables, chicken, feathers of birds, blood cells from other persons or animals, drugs, and chemicals can also induce the immune system to produce antibodies.
  Antibodies are an army of proteins produced by plasma cells.

Structure of Antibody (Ig)

• Antibodies (immunoglobulins, abbreviated Ig) are glycoproteins of molecular weight 150,000-900,000 kD.
• One end of the Ig binds to the antigens (the Fab portion, so called because it is a fragment of the molecule which is antigen binding), and the other end which is crystallizable, and therefore called Fc, is responsible for effector functions.
• There are five classes (isotypes) of Ig: IgM, IgG, IgA, IgD, and IgE.
• Light chains exist in two classes: lambda and kappa. Each antibody molecule has either lambda or kappa light chains, not both.
• Immunoglobulins are found in serum and in secretions from mucosal surfaces.
• They are produced and secreted by plasma cells which are found mainly within the lymph nodes and connec- tive tissues and do not circulate.
• Plasma cells are derived from B-lymphocytes.
• These cells are responsible for secreting antibodies, i.e., immunoglobulins.
• An immunoglobulin molecule consists of two light chains (each of approximate molecular weight 25,000) and two heavy chains (each of approximate molecular weight 50,000).
• IgA exists in monomeric and dimeric forms while IgM exists in pentameric form.
• The links between monomers are made by a J chain. Additionally, IgA molecules receive a secretory component from the epithelial cells into which they pass.
• This is used to transport them through the cell and remain attached to the IgA molecule within secretions at the mucosal surface.

• The heavy and light chains consist of amino acid sequences.
• In the regions concerned with antigen binding, these regions are extremely variable, whereas in other regions of the molecule, these are relatively constant. Thus, each heavy and each light chain possesses a variable and a constant region.
• The isotype of an Ig is determined by the constant region.
• L-chains are linked with H-chains by disulfide (S-S) links. Intrachain S-S links divide H- and L-chains into domains that are separately folded.
• Antibodies are synthesized by B-lymphocytes and exist in two forms: either membrane bound or secreted.
• B-lymphocytes use membrane-bound antibody to interact with antigens.
• B-cell makes antibodies all of the same specificity, i.e., able to react with the same antigenic determinants; its progeny (as a consequence of mitotic division) is referred to as a clone.
• The clone will continue making antibody of the same specificity.
• Simultaneously, there will be lots of other clones of different specificity.
• This is known as a polyclonal response.
• Antigens have determinants called epitopes.
• Epitopes are molecular shapes recognized by antibodies, which recognize one epitope rather than the whole antigen.
• Antigens may be proteins, lipids, or carbohydrates; an antigen may consist of many different epitopes and/or may have many repeated epitopes.
• B-lymphocytes evolve into plasma cells under the influence of T-cell released cytokines.
• Plasma cells secrete antibodies in greater amounts, but do not divide.
• These exist in lymphoid tissues, not blood.
• Plasma cells make and release between 2000 and 20,000 antibody molecules per second into the blood for the next four or five days.
• B memory cells live for months or years, and are a part of the immune memory system.
• B-lymphocytes are formed within the bone marrow and undergo their development.
• They have the following functions:
  • To interact with antigenic epitopes, using their immunoglobulin receptors.
  • To subsequently develop into plasma cells, secreting large amounts of specific antibody.
  • To circulate as memory cells.
  • To present antigenic peptides to T-cells (as antigen presenting cells).

Main Functions of Free (Soluble) Antibodies

• Antibodies exist free in body fluids, e.g., serum, and membrane bound to B-lymphocytes.
• Their function, when membrane bound, is to capture antigen for which they have specificity, after which the B-lymphocytes will take the antigen into its cytoplasm for further processing.
• Free antibodies cause the agglutination of particulate matter, including bacteria and viruses.
• IgM is particularly suitable for this, as it is able to change its shape.
• Opsonization is the coating of antigen by molecules known as opsonins for which the antibody’s Fab re- gion has specificity (especially IgG).
• Even complement system takes part in opsonization especially C3b molecule.
• This facilitates subsequent phagocytosis by cells possessing an Fc receptor, e.g., neutrophil (polymorphonuclear leucocytes or polymorphs).
• Hence, opsonization is the process that facilitates the phagocytosis of antigen.
• Thus, it can be seen that in opsonization and phagocytosis, both the Fab and the Fc portions of the immunoglobulin molecule are involved.
• Neutralization of toxins released by bacteria, e.g., tetanus toxin is neutralized when specific IgG antibody binds, thus, preventing the toxin binding to motor end plates and causing persistent stimulation, manifest as sustained muscular contraction which is the hallmark of tetanic spasms.
• Other B-cells circulate as memory cells.
• This applies particularly to IgG.
• B-cells divide, forming plasma cells and B memory cells.
• In case of viruses, antibodies can hinder their ability to attach to receptors on host cells. Here, only Fab is involved.
• Antibodies against bacterial cilia or flagella will hinder their movement and ability to escape the attentions of phagocytic cells.
• Mucosal protection is provided mainly by IgA, and to a lesser degree, by IgG.
• IgA acts chiefly by inhibiting pathogens from gaining attachment to mucosal surfaces.

• As a consequence of antigen (e.g., parasitic worms) binding to specific IgE attached to the mast cells by their receptor for IgE, there is a release of mediators from the mast cells.
• This leads to the contraction of smooth muscle, which can result in diarrhea and expulsion of parasites.”
• Precipitation of soluble antigens by immune complex formation
  • Consist of antigen linked to antibody.
  • Depending on the ratio of antigen to antibody, these can be of varying size.
  • When fixed at one site, these can be removed by phagocytic cells.
  • These may also circulate prior to localization and removal, and can fix complement.
• Antibodies bind to organisms via their Fab region.
• Large granular lymphocytes (NK cells) attach via Fc receptors and kill these organisms not by phagocytosis but by the release of toxic substances called perforins.

Five Classes (Isotypes) of Antibodies

• IgA forms 15% of total antibody count. It is found in the mucous secretions of the respiratory tract and the upper parts of the digestive tract and the vagina. It is also found in colostrum. Colostrum is a golden liquid substance that a nursing mother expels from her breasts 24-48 h after delivery. This substance is produced before the milk and is very important in the transfer of antibodies to a newborn infant. IgA given by the mother in the colostrum protects the baby for about 6 months. Oimeric IgA has four paratopes.
• IgD forms less than 1% of the total antibodies. It appears to have a role in activating and suppressing lymphocyte activity found in large quantities in the cell walls of many B-cells. IgO has two paratopes.
• IgE is less than 1% of the total antibodies. It is mediator in allergic responses. It most importantly activates histamine secreting cells. It also appears to play a role in parasitic infection. IgE has two paratopes.
• IgG composes 75% of our immunoglobulin pool. It stimulates phagocytic cells, activates the complement system, binds neutrophils, opsonizes, and can neutralize toxins. Most importantly, it is the only antibody that can cross the placenta and confer immunity on the fetus. IgG also has two paratopes.
• IgM makes up 7-10% of our total antibodies. This is the predominant early antibody the one that first activates in an initial attack of antigen. Because of its high number of antigen-binding sites (10), it is an effective agglutinator of antigen. This is important in the initial activation of B-cells, macrophages, and the complement system.

Mode of Action of T-cells to Antigens or Cell-Mediated Immunity

• T-cells are the major cells that drive cellular immunity whereas another type of lymphocyte, called as B-cells, is the principle cell involved with antibody-mediated immunity.
• T-cells are so called because they are matured in an organ called the thymus.
• The surface of a T-cell contains thousands of T-cell receptors (TCR) but for any one T-cell, all receptors are identical (monoclonal).
• This means that any one T-cell is only able to recognize a small group of related antigens, i.e., each T-cell is specific only to those antigens and is not effective against any others.
• The receptor rarely binds with an entire antigen but with a subsection of it called an epitope.
• The function of T-cells is to detect cells in the body that are internally infected with viruses and bacteria. Intra-cellular pathogens do this by sampling the contents of cells.
• Two types of T-cells sample different populations of cells and take different action when they detect an antigen.
• These are the “killer” or cytotoxic (CD8+) T-cells and the “helper” (CD4+) T-cells.
• CD8+ and CD4+ describe the types of receptors that each carries.
• A third type of T-cells called “suppressor” T-cells also uses the CD8+ receptor.
• Almost all cells in the body express a protein called the MHC protein.
• The function of MHC is to present antigens to T-cells. MHC has a slit in it, shaped like a letter box, and the
• cell pushes antigens through this slit.
• T-cell receptors plug onto the MHC molecule and try to bind with the presented antigen.
• MHC comes in two major varieties: MHC class 1 and MHC class 2.
• MHC class 1 is present on almost all nucleated cells and it is the job of killer T-cells to bind to antigens. presented in this way.
• When a match is found, the killer T-cell latches onto the infected cell and destroys it.
• MHC class 2 is present only on a population of cells known as APC.
• These include macrophages, B-cells, and dendritic cells. It is the job of helper T-cells to bind to antigens presented in this way.
• When this happens, a helper T-cell can do several things such as the following:
  • It produces special messenger molecules called cytokines. Various different cytokines send different complex signals to other cells including attracting immune system cells to the site of the infection, causing endothelial (blood vessel lining) cells to let these other cells through, and causing the immune system cells to activate themselves.
  • It cooperates with complementary B-cells to get them to clone themselves and to release antibodics.
  • T-cells clone themselves to increase their number.
• Helper T-cells are strongly implicated in the process of demyelination in multiple sclerosis.
• The third type of T-cells (suppressor T-cells) is involved with suppressing an immune response.
• It is not well understood how they do but they probably use several mechanisms including “programmed cell death” (apoptosis) which involves sending cytokines to other immune system cells telling them to commit suicide.
• T-cells are manufactured in the bone marrow but migrate to an organ called the thymus where they are matured via a process called affinity maturation which removes those which are active against body’s own antigens (auto-reactive).
• Selection for particular T-cells is dealt with in the entry on the thymus.
• Helper T-cells are CD4 cells that become activated when they encounter the antigens now displayed on the macrophage surface.

Clonal Selection and Primary and Secondary Immune Responses

• Each B- and T-lymphocyte displays on its surface a specific receptor; the number of cells expressing a given receptor is rather small.
• In case of a B-cell, this receptor is the antibody produced by that cell.
• When this receptor interacts with the antigenic determinant specific to it, the lymphocyte becomes activated and divides to form a clone of cells.
• These cells are also transformed into effector cells, i.e., antibody producing B-cells and T cytotoxic cells.
• This phenomenon is called clonal selection, where all cells in a given T- or B-cell clone are derived from a single parental cell and exhibit the same specificity for antigenic determinant.
• But some activated lymphocytes develop into long lived memory cells and do not produce antibodies or kill infected cells.

• The immune response mounted as a result of the first encounter of an animal with an antigen takes relatively longer, is feeble, and declines rapidly.
• This is known as primary immune response.
• But a subsequent encounter of this animal with the same antigen results in a hightened immune response much more rapidly.
• This is referred to as secondary immune response or anamnestic response.
• The secondary response is due to the memory cells that were produced during primary response; it lasts much longer than primary response.
• This is why a person surviving a disease such as chicken pox or measles becomes immune to subsequent attacks of the same disease.

Development of Immunity

A person may develop immunity in three ways:

• Vaccination: It is a technique to develop immunity without infection. Weakened or dead pathogens (attenuated) or parts of pathogens are injected into a person who is required to be made immune. The pathogens given in a vaccine are unable to cause the disease but are sufficient to stimulate the formation of antibodies by the host’s immune system. Often 2 or 3 additional doses are needed to generate adequate immunity. These doses are called booster doses.
• Antitoxins: Antibodies that neutralize toxins produced in the body or introduced from outside are called antitoxins. Bacterial toxins are produced in the body; however, antitoxins produced from outside are prepared from snake venom and are used as a remedy for snake bite.
• Immunity through diseases: Some diseases such as mumps, measles, and smallpox produce lifelong immunity. Hence, these diseases do not appear again.

Types of Immunity

There are two main types of immunity: Inborn or innate and acquired or adaptive.

• Inborn or innate immunity: This type of immunity is inherited by the organism from his parents and it protects him from the birth till the end of life. Example: Human beings have inborn immunity against distemper (a fatal disease of dogs).
• Acquired or adaptive immunity: This immunity is acquired in lifetime. It is of two types: Active or natural and passive or artificial.
  • Active immunity: When an organism’s own cells produce antibodies, it is called active immunity. It develops when a person suffers from a disease or gets vaccination for a disease.
  • Passive immunity: In passive immunity, the antibodies are produced in some other organisms (e.g., vertebrates) in response to the given antigen. These antibodies are then injected into the human body at the time of need. This is known as inoculation. For example, persons infected by rabies, tetanus, Salmonella (causes food poisoning), and snake venom are given sufficient amount of antibodies so that they can survive.
• Passive immunity provides immediate relief while active immunity requires some time for the formation of antibodies.
• There is another form of passive immunity. Nursing mothers transfer antibodies prepared in their body to the infants in their milk. Bottle-fed infants do not get this benefit. After a few weeks, infants’ own immunity system starts working.

History of Vaccination and Immunization

• In vaccination, weakened or dead pathogens, or portions of pathogens, are injected into a person who is required to be made immune.
• Pathogens given in a vaccine are unable to cause the disease but are sufficient to stimulate the formation of antibodies by host’s cells.
• The process of vaccination was initiated by Edward Jenner in 1790.
• He observed that milkmaids did not contract smallpox apparently because they were exposed to a similar but milder form of disease called cowpox.
• Edward Jenner infected James Phipps, a healthy boy of about 8 years, first with cowpox and two months later, he infected the boy with smallpox.
• The boy did not suffer from smallpox.
• Jenner proposed that an induced mild form of a disease would protect a person from a virulent form (which has ability to damage the host).
• He used the term vaccine (in Latin Vacca means “cow”) and the term vaccination for protective inoculation.
• Edward Jenner was the first to discover a safe and effective means of producing artificial immunity against smallpox.
• Thus, once vaccination is done, the individual is protected from the disease.
• Vaccination develops acquired immunity.
• Pasteur confirmed Jenner’s findings and produced vac- cines for other diseases such as anthrax, rabies, and chicken cholera.
• In 1891, another daring step was taken which added to the growing understanding of immunology.
• A little girl lay dying of diphtheria.
• Her physician, Emil von Behring, decided to gamble on her life.
• He infected sheep with diphtheria bacteria and waited for some time.
• He then withdrew some blood from the sheep and separated the serum by allowing it to clot.
• He injected the serum into the patient.
• Within a few hours, she began to recover dramatically. A new method of treatment-passive immunity had been discovered.
• von Behring was awarded the Nobel Prize for this work.
• Passive immunization is the practice of taking antibodies produced by a vertebrate, in response to deliberate infection, and transferring them to a different organism by injection.
• For instance, persons infected by rabies or Salmonella (that causes food poisoning) are likely to succumb to the disease as they would not be able to produce sufficient amounts of antibodies quickly.
• To avert death, such persons are inoculated with anti-bodies produced in the plasma of horses or cow. This provides passive immunity.

Immune System Disorder

Improper functioning of immune system can cause, discomfort, disease, or even death. These disorders may involve the following:

• Hypersensitivity or allergy:
  • Allergy means inappropriate and excessive response to common antigens.
  • Substances causing allergic reaction are called allergens.
  • Common allergens are dust, pollen, mold, spores, fabrics, feathers, fur, plants, bacteria, foods, heat, cold, and sunlight.
  • Parthenium flower is a common allergen in India.
  • Allergy mostly affects the skin and the mucous membrane.
  • Hay fever affects the mucous membranes of nose, eyes, and upper respiratory tracts.
  • In asthma, the lower portions of the respiratory system are severely affected.
  • In eczema, the skin becomes red, followed by the appearance of minute blisters.
  • During allergic reaction, there is an increased release of histamine from the mast cells.
  • It causes marked dilation of all peripheral blood vessels and the capillaries become highly permeable so that large amount of fluid leaks out from the blood into the tissues.
  • The blood pressure decreases drastically often resulting in the death of the individual within a short time.
  • Spleen is called the “shock organ of allergy.”
  • The exact nature of the substance of which a person is hypersensitive must be known before he can be properly treated.
  • Some forms of allergy are as follows:
    • Hay fever: In this allergic form, there are swollen, reddened, running eyes and nose. The drugs called antihistamines are of major importance in the treatment of this allergic disorder.
    • Asthma: It is the sudden spasm of tissue surrounding the respiratory tract causing the narrowing of respiratory tract. The tissues surrounding the respiratory tubes in the lungs swell up and compress the tubes. Hence, there is difficulty in breathing.
    • Anaphylactic shock: It is an allergic reaction involving all the tissues of the body and occurs in a few minutes after the injection of an antigen such as penicillin. Such reaction is very serious. Histamine released from ruptured mast cells causes marked dilation of all the arteries so that a large amount of fluid is passed from the blood to the tissues and there is a drastic fall in blood pressure. The affected person may become unconscious and may die within a short time.
• Autoimmunity
  • Antibodies are produced against antigens but, sometimes, it may also happen that the immune system of the body goes off the track and starts behaving against the “own body” or “self.”
  • This leads to a variety of diseases known as autoimmune diseases.
  • This type of diseases depends on the type of “selfantigen” involved.
  • When the cells act as antigens in the same body, they are called autoantigens.
  • The nature of autoimmune diseases depends on the autoantigens involved.
  • For example, if the autoantigens are RBCs, then the body destroys its own RBC resulting in chronic anemia; if the autoantigens are produced against acetylcholine receptors (Myasthenia gravis); if the autoantigens are liver cells, then it results in chronic hepatitis; and so on. Other autoimmune diseases are insulin-dependent diabetes, Addison’s disease, ulcerative colitis, and rheumatoid arthritis.
• Immuno deficiencies
  • Severe combined immuno deficiency
    • Sometimes, new-born children are without T- cells and B-cells.
    • These children are highly susceptible to various infections.
    • The most serious disorder of this type is a congenital disease known as severe combined immuno deficiency (SCID) in which both B-cells and T-cells are not present in the body.
    • Such children are highly susceptible even to minor infections.
    • In developed countries such as USA, such children are kept alive by keeping them in germ-free environments called isolation suits.
  • AIDS
    • It is a disorder of cell-mediated immune system of the body.
    • There is a reduction in the number of helper T-cells which stimulate antibody production by B-cells.
    • This results in the loss of natural defense against viral infection.
• Graft rejection
  • Grafts of kidney, heart, lung, liver, etc., from one human to another are always (unless donated by an identical twin) seen by the recipient’s immune system as an antigenic and elicit immune response.
  • If unchecked, this response will eventually lead to the destruction of the graft. Both CD4+ and CD8+ T-cells participate in graft rejection.
  • They are responding to differences between donor and host of their class II and class I histocompatibility molecules, respectively.
• Graft-versus-host disease
  • Grafts of bone marrow are used to provide, or restore, a source of blood cells for the recipient.
  • If there are any histocompatibility differences between donor and recipient (and there always are some, unless the patient’s own marrow is used or that of an identical twin), then the T-cells of the donor will mount an immune response against the tissues of the recipient.
  • Fortunately, graft-versus-host disease can usually be controlled with immunosuppressive drugs.

Cancer

• Cancer is characterized by the uncontrolled multiplication of abnormal cells in the body.
• The spread of cancerous cells to distant sites via blood is termed as metastasis.
• Normally, cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth, but cancer cells have lost this property.
• It may be broadly classified into three major categories:
  • Carcinomas are malignant growths of epithelial (ectodermal) tissues that cover or line the body organs, e.g., skin cancer, breast cancer, lung cancer, and cancer of the stomach and pancreas. (About 85% of all tumors are carcinoma.)
  • Sarcomas are malignant growths arising in tissues derived from primitive mesoderm, e.g., bone tumors, muscle tumors, and cancer of lymph nodes. These are rare in human beings (about 1% of all tumors).
  • Leukemias result from the unchecked proliferation of cell types present in blood and their pre- cursors in the bone marrow.
• Cancer is a complex group of diseases that can affect many different body cells and tissues.
• All cancers are characterized by the uncontrolled growth and division of cells.
• Cancer leads to a mass of cells termed as neoplasm (Gr. for new formation) or tumor.
• Abnormal and persistent cell division localized in a particular region is called benign tumor.
• Benign tumor contains well-differentiated cells, not usually dangerous.
• Tumor cells may be carried by bloodstream or lymph or may penetrate directly to the other parts of the body resulting in dangerous malignant tumors. The spread of cancerous cells to distant sites is termed as metastasis.
• Other types of cancers are as follows:
  • Melanoma: Cancer of pigment cells of the skin
  • Adenoma: Cancer of glands
  • Myoma: Cancer of muscular tissue
  • Lymphoma: Cancer of lymphatic tissue
  • Glioma: Cancer of glial cells of CNS
• Oncology is the study of cancer.
• All cells carry certain cancer-associated proto-oncogenes.
• Susceptibility to cancer depends on familial factors, smoking, chemical and environmental factors, viral factor, alcohol, and dietary factors.
• Any agent that induces a cancer is carcinogenic or oncogenic agent.
• Exposure to ionizing radiations such as X rays, gamma rays, and non-ionizing UV rays is said to induce cancer.
• Chemical substances that can cause mutation are called carcinogens.
• Physical irritants can also lead to cancer such as continued abrasion of the lining of the intestinal tract by some type of food.
• In many families, there is a strong hereditary tendency to cancer.
• Viruses cause a number of specific cancers in animals.
• Tumor-producing viruses are called oncoviruses.

• Viruses are the second cause of cancer.
• These agents are tiny packages of nucleic acids, either DNA or RNA, that are capable of infecting cells and converting them to virus-producers.
• Although the link between viruses and cancer is strongly established for a variety of animal cancers, the relation in human cancers is less predictable.
• Clearly, the number of people infected with these viruses is much larger than the number that develops cancer.
• But evidence suggests that chronic viral infections are associated with up to one-fifth of all cancers. These include the following:
  • Human T-cell leukemia virus-1 (HTLV-1): It is associated with leukemia (a malignant disease of blood-forming tissues) and lymphoma (a cancer of lymphatic tissue).
  • Human immune deficiency virus (HIV): It is associated with KS, a cancer of blood vessels in the skin.
  • Epstein-Barr virus (EBV): It causes infectious mononucleosis, associated with Burkitt’s lymphoma (a cancer of white blood cells), nasopharyngeal carcinoma (common in Chinese males), and Hodgkin’s disease (a lymphatic system cancer). Here, Burkitt and Hodgkin are the names of discoverers.
  • Hepatitis B virus (HBV): It is associated with liver cancer.
  • Human papilloma virus (HPV): It causes genital warts (benign growths) associated with the cancer of cervix, vagina, penis, and colon.
  • Type 2 herpes simplex virus: It causes genital herpes, implicated in the cancer of cervix of the uterus.
• Cancer may cause a variety of minor symptoms. Any that persist for several days should be checked by a doctor. The earlier a cancer is diagnosed, the better the chance of cure. Some symptoms are as follows:
  • Rapid weight loss without apparent cause.
  • A scab, sore of ulcer that fails to heal within 3 weeks.
  • A blemish or mole that enlarges, bleeds, or itches. Severe recurrent headaches.
  • Difficulty in swallowing (persistent hoarseness of voice)
  • Coughing of blood sputum (phlegm).
  • Change in shape or size of testes.
  • Blood in urine, with no pain on urination.
  • Change in bowel habits.
  • Lump or change in breast shape.
  • Bleeding or discharge from nipple.
  • Vaginal bleeding or spotting between periods or after menopause.
• Cells of malignant tumors duplicate continually and very often quickly and without control.

• Such an increase in the number of cells due to an in- crease in the frequency of cell division is called hyperplasia.
• Initially, malignant cells invade surrounding tissues. As the cancer grows, it expands and begins to compete with normal tissues for space and nutrients.
• Eventually, the normal tissue decreases in size (atrophies) and dies.
• Following the nearby invasion, some malignant cells may detach from the initial (primary) tumor.
• They may invade a body cavity or enter the blood or lymph, which can lead to widespread metastasis.
• Next, those malignant cells that survive in the blood or lymph invade other body tissues and establish secondary tumors.
• Finally, the secondary tumors become vascularized.
• They undergo angiogenesis, which is the growth of new networks of blood vessels.
• Any new tissue, whether it results from repairing a wound, normal growth, or tumors, requires a blood supply to deliver nutrients and oxygen.
• Proteins that serve as chemical triggers for blood vessel growth in tumor tissue are called tumor angiogenesis factors (TAFS).
• In all stages of metastasis, the malignant cells resist the antitumor defenses of the body.
• The pain associated with cancer develops when the growth puts pressure on nerves or blocks a passage-way so that secretions build up pressure.

Cancer Detection and Diagnosis

• Early detection of cancers is essential as it allows the disease to be treated successfully in many cases.
• Cancer detection is based on biopsy and histopathological studies of the tissue and blood, and bone marrow tests for increased cell counts in case in leukemias.
• In biopsy, a piece of suspected tissue cut into thin sections is stained and examined under microscope (histopathological studies) by a pathologist.
• Techniques such as radiography (use of X rays), CT (computed tomography), and MRI (magnetic resonance imaging) are very useful to the detect cancers of internal organs.
• MRI is the safest method for detection of cancer. CT uses X rays to generate a three-dimensional image of the internal structure of an object.
• MRI uses strong magnetic fields and non-ionizing radiations to accurately detect pathological and physiological changes in the living tissue.
• Antibodies against cancer-specific antigens are also used for the detection of certain cancers, e.g., Herceptin.
• Monoclonal antibodies are used for the diagnosis of breast cancer.
• Techniques of molecular biology can be applied to detect genes in individuals with inherited susceptibility to certain cancers.
• Identification of such genes, which predispose an individual to certain cancers, may be very helpful in the prevention of cancers.
• Such individuals may be advised to avoid exposure to particular carcinogens to which they are susceptible (e.g., tobacco smoke in case of lung cancer).

Treatment of Cancer

• Common approaches for the treatment of cancer are surgery, radiation therapy, and immunotherapy.
• In radiotherapy, tumor cells are irradiated lethally, taking proper care of the normal tissues surrounding the tumor mass.
• Several chemotherapeutic drugs are used to kill cancerous cells.
• Some of these are specific for particular tumors.
• Majority of drugs have side-effects such as hair loss and anemia.
• Most cancers are treated by the combination of surgery, radiotherapy, and chemotherapy.
• Tumor cells have been shown to avoid detection and destruction by immune system.
• Therefore, patients are given substances called biological response modifiers such as interferon, which activate their immune system and help in destroying the tumor.
• A common weed, Catharanthus roseus (Vinca rosea or Sadabahar), is the source of two anticancer drugs, Vincristin and Vinblastin, used in the treatment of leukemia.

AIDS

• AIDS is a deadly disease, caused by HIV, which mounts a direct attack on all cells that have a specific protein called CD4 on their surfaces.
• CD4 is found on a class of lymphocyte cells called T4- cells.
• This class includes helper T-cells, which is why HIV destroys the body’s population of helper T-cells.
• CD4 receptors are also found on macrophage surfaces, and as a result, macrophages also become infected with HIV.
• Much of the HIV transmission from one individual to another is thought to occur within macrophages passed as a part of body fluids.
• Macrophages, thus, act as HIV factory.
• A simplified definition of AIDS includes anyone infected with HIV and having a T4 lymphocyte count under 200/mm3 of blood. (Normally, the T4 count would be about 1200/mm3.)
• AIDS was first recognized in June 1981 as a result of reports from the Los Angeles area (USA) to the Center for Disease Control and Prevention (CDC) of several cases of a very rare type of pneumonia caused by a fungus.
• The pneumonia, called Pneumocystis carinii pneumonia (PCP), occurred among homosexual males.
• At about the same time, the CDC also received reports from New York and Los Angeles concerning an in- crease in the incidence of (KS) amongst homosexual males.
• AIDS was first recognized in the USA in 1981.
• In 1984, American and French scientists independently identified the agent as a virus.
• Americans named it HCLV-III (human cell leukemia virus-3).
• The name human immune deficiency virus is now preferred.
• There are two types of HIV, namely HIV-1 and HIV- 2; the most common virus currently associated with AIDS is HIV-1.
• A virus called the Simian immuno deficiency virus (SIV) found in the blood of wild African green mon- key is similar to HIV-2.
• The genome of HIV consists of two identical molecules of single-stranded RNA and is said to be diploid.
• HIV consists of a core RNA with reverse transcriptase surrounded by a protein coat.
• The protein coat around the core consists of a protein called P24.
• Outside this protein coat is a layer composed of another protein called P17.
• The outermost envelope consists of a phospholipid bilayer studded with glycoproteins (GP120 and GP41).
• HIV is a retrovirus; using the enzyme reverse transcriptase, it can synthesize DNA from RNA.
• Once HIV produces DNA from its RNA, the DNA is integrated into the host cell’s DNA.
• There it can remain dormant, giving no sign of its presence, or it can take over the host cell’s genetic machinery to produce more viruses.
• The major cell infected by HIV is the helper T-lymphocyte that bears the CD4 receptor site.
• The attachment of the virus of CD4 receptor site occurs with the help of GP120 on the protein coat of the virus.
• HIV enters body cells by receptor-mediated endocytosis.

• The receptor of docking protein that permits HIV entry is the CD4 molecule on the surface of T4 cells, although other cellular factors, not yet understood, must also contribute.
• With time, the number of T4 cells, mainly helper T- cells, declines due to the death of infected cells.
• The result is progressive collapse of the immune system.
• Since cytokines secreted by helper T-cells normally stimulate the activity of monocytes, neutrophils, and macrophages, non-specific defense mechanisms are also depressed.
• The person becomes susceptible to opportunistic infections-invasion of normally harmless microorganisms that now proliferate wildly because of the defective immune system.
• Besides PCP, AIDS victims have persistent diarrhea and are especially susceptible to toxoplasma infections (tuberculosis), leukoplakia (whitish patches on mucous membranes primarily due to yeast infections), cytomegalovirus (leading to blindness and dementia), and Herpes simplex, among many other bacterial and fungal infections.
• The AIDS virus infects macrophages, brain cells (where HIV-infected cells may release toxins that dis- rupt and kill other brain cells), as well as T4 cells. The most common HIV-related opportunistic infec- tions are PCP and KS (a cancer of the skin).
• The clinical symptoms of AIDS usually appear when the T-lymphocyte level falls below 200/mm3.
• The median time for survival after the diagnosis of AIDS is 2 years.
• Some people with AIDS live for 6 or more years while others survive for a few months only.
• Some weeks after infection with HIV, the host develops antibodies against several proteins in the virus.
• Antibodies normally are protective because they help eliminate an intruder.
• In the case of AIDS virus, this is not necessarily the case because HIV can remain hidden inside body cells, unavailable to form antigen-antibody complexes.
• HIV may also escape detection by cytotoxic T-cells, natural killer cells, and phagocytes.
• The virus further evades immune defenses by undergoing rapid antigenic changes in its surface proteins. Moreover, infected cells displaying viral antigens can fuse to uninfected cells and spread the virus that way.
• In rare cases, a person may harbor HIV without forming antibodies against it.
• Thus, a standard blood test that detects antibodies would be negative.

• The presence of nucleic acids from HIV can still be detected using a method called the polymerase chain reaction (PCR).
• Once the host is infected by HIV, a detectable antibody response occurs in most cases within 6-8 weeks.
• HIV antibodies can be detected by the ELISA test (enzyme-linked immunosorbent assay).
• A positive ELISA should be confirmed using another test called the western blot test.
• Although HIV has been isolated from several body fluids, the only documented transmissions are from blood, semen, or vaginal secretions or by way of breast milk from a nursing mother to her baby.
• The virus is found free and in macrophages in these fluids.
• HIV is transmitted by sexual contact most commonly. It is also effectively transmitted through the exchanges of blood, e.g., by contaminated hypodermic needles, contact with open wounds, or using the same razor blade for shaving.
• Infected mothers may transmit the virus to their infants before or during birth.
• It does not appear that people become infected as a result of routine nonsexual contact.
• There is no known case of transmission from a mosquito bite.
• It also appears that healthcare personnel who take proper routine barrier precautions when dealing with body fluids (gloves, masks, and safety glasses) are not at risk unless the barriers fail.
• Outside the body, HIV is fragile and can easily be eliminated.
• For example, dish-washing and clothes-washing; ex- posing the virus to 135°F (56°C) for 10 min will kill HIV.
• Chemicals such as hydrogen peroxide (H2O2), rubbing alcohol, household bleach, and germicidal skin cleaner (such as Dettol) are also very effective, as is standard chlorination in swimming pools and hot tubs.
• Medical scientists are engaged in an immense effort to find a cure for AIDS.
• One of the problems in treating AIDS is that HIV can lie undetected in body cells.
• In addition, HIV can infect a variety of cells, including those in the central nervous system that are protected by the blood-brain barrier.
• Added to this is the problem of oppertunistic infec- tions, which may be very difficult to treat.
• Any therapy must overcome the problem that antiviral agents may also harm host cells.
• Thus, scientists are trying to devise strategies for disrupting specific viral activities.
• Some research centers on preventing the binding of virus to the host CD4 protein.
• Other strategies are to prevent the conversion of RNA to DNA, which is catalyzed by reverse transcriptase, to block the processing of viral proteins by specific viral enzymes, to inhibit the assembly of viruses within the host cell, and to thwart release of new viruses.
• To date, four drugs with similar action are used to inhibit HIV replication and slow the progression of AIDS.
• All are nucleoside analogs-substances that are similar to the naturally occurring nucleosides in RNA and DNA.
• They block the conversion of retroviral RNA into DNA.
• The first and still most commonly used drug to treat AIDS is AZT (azidothymidine) or Retrovir.
• Among patients taking AZT, there is a slowing in the progression of symptoms.
• The main side-effects are red bone marrow damage and anemia.
• Eventually, the virus develops resistance to the drug.
• Other drugs are DDI (dideoxyinosine), DDC (dideoxycytidine), and D4T (stavudine), which may be used in patients who do not respond to AZT or have become resistant to it.
• Doctors generally give Zidovudine and Nevirapine to HIV positive pregnant women to ensure that their babies do not carry the infection.

Prevention of AIDS

• As AIDS has no cure, prevention is the best option. Moreover, HIV infection more often spreads due to conscious behavior patterns and is not something that happens inadvertently, like pneumonia or typhoid.
• Of course, infection in blood transfusion patients, new-borns (from mother), etc., may take place due to poor monitoring.
• The only excuse may be ignorance, and it has been rightly said, “Don’t die of ignorance.”
• In our country, the National AIDS Control Organization (NACO) and other non-governmental organization (NGOs) are doing a lot to educate people about AIDS.
• WHO has started a number of programs to prevent the spreading of HIV infection.
• Making blood (from blood banks) safe from HIV, ensuring the use of only disposable needles and syringes in public and private hospitals and clinics, free distribution of condoms, controlling drug abuse, advocating safe sex, and promoting regular check-ups for HIV in susceptible populations are some such steps taken up.
• Infection with HIV or having AIDS is something that should not be hidden since then the infection may spread to more people.
• HIV/AIDS-infected people need help and sympathy instead of being shunned by society.
• Unless society recognizes it as a problem to be dealt with in a collective manner, the chances of wider spread of the disease increase manifold.
• It is a malady that can only be tackled by the society and medical fraternity acting together to prevent the spread of the disease.

Cirrhosis

• Cirrhosis refers to a distorted or scarred liver as a result of chronic inflammation.
• The parenchymal (functional) hepatocytes are replaced by fibrous or adipose connective tissue.
• The symptoms of cirrhosis include jaundice, edema in the legs, uncontrolled bleeding, and increased sensitivity to drugs.
• Cirrhosis may be caused by hepatitis (inflammation of the liver), certain chemicals that destroy hepatocytes, parasites that infect the liver, and alcoholism.

Hepatitis

• Hepatitis refers to the inflammation of liver and can be caused by viruses, drugs, and chemicals, including alcohol. Clinically, several viral types are recognized. Hepatitis A (infectious hepatitis) is caused by hepatitis A virus and is spread by fecal contamination of food, clothing, toys, eating utensils, and so forth (feco-oral route). It is generally a mild disease of children and young adults characterized by anorexia (loss of appetite), malaise, nausea, diarrhea, fever, and chills. Eventually jaundice appears. Most people recover in 4-6 weeks. Hepatitis A virus has single-stranded RNA genome and non-enveloped capsid.
• Hepatitis B (serum hepatitis) is caused by hepatitis B virus. HBV is a 42 nm enveloped virion, containing partially double-stranded circular DNA genome. Within the core there is DNA-dependent DNA polymerase. It is spread primarily by sexual contact and contaminated syringes and transfusion equipment. It can also be spread by saliva and tears. Hepatitis B virus can be present for years or even a lifetime and can produce cirrhosis and possibly cancer of the liver. Persons who harbor active hepatitis B virus are at risk for cirrhosis and also become carriers. Vaccines produced through recombinant DNA technology (e.g., Recombivax HB-second-generation vaccine) are available to prevent hepatitis B infection.
• Hepatitis C (non-A, non-B hepatitis) is caused by hepatitis C virus. It is clinically similar to hepatitis B and is often spread by blood transfusions. Hepatitis C can cause cirrhosis and possibly liver cancer. It has enveloped virion with ssRNA.
• Hepatitis D (delta hepatitis) is caused by hepatitis D virus which has ssRNA. It is transmitted like hepatitis B. In fact, a person must be co-infected with hepatitis B before contracting hepatitis D. Hepatitis D results in severe liver damage and has a fatality rate higher than that of people infected with hepatitis B virus alone. HDV is a defective virus for which HBV is the helper.
• Hepatitis E (infectious NANB hepatitis) is caused by hepatitis E virus and is spread like hepatitis A. Although it does not cause chronic liver disease, hepatitis E virus is responsible for a very high mortality rate in pregnant women. HEV has ssRNA.

Mental Health

• Mental illness is characterized by the following symptoms:
  • Depression
  • Insomnia (lack of sleep) or excessive sleeping
  • Compulsive actions.
  • Feeling of hopelessness
  • Serious thoughts of suicide
  • Unreasonable phobias
  • Partial or complete loss of memory
  • Self-destructive behavior, e.g., excessive gambling, drinking, drug abuse, over-eating, and extreme dieting
  • Delusions (false beliefs) and hallucinations Vocational and social dysfunctioning on a day-to-day basis.
• Hallucination is a subjective disorder of sensory perception, in which one of the senses is involved in the absence of external stimulations.

Psychological Disorders

• Psychological disorders include psychosis and neurosis. Psychosis involves deeper mental disorientation due to a distorted sense of reality.
• Neurosis, on the other hand, is a maladaptive habit.
• Neurotic individual relates to the same “real world” as does the normal individual, but cannot effectively act upon it. Important psychological disorders are as follows:
  • Anxiety disorders: It is associated with a range of unpleasant bodily symptoms, including palpitation, sweating, nausea, trembling, diarrhea, and muscular tension.
  • Obsessive-compulsive disorders: These disorders cause total disability and affect a person’s waking hours. Affected persons manifest over whelming obsessions and compulsions. They are compelled to perform an action or an idea despite their own attempt to resist it (compulsion). The most common obsessions are violence, concern about infection by germs or dirt, and constant doubts (obsessions).
  • Attention deficit disorder: It is a mental health problem among children. It occurs more in boys than in girls. As a result of this disorder, boys exhibit under achievement, behavioral problems, and a tendency to be disliked by other children.
  • Mood disorders: These are the occasional bouts of high or low mood, i.e., elation and depression. Depression is a mood disorder characterized by sadness; hopelessness; low self-esteem; decline in interest, energy, and concentration; and changes in sleep pattern and appetite.
  • Schizophrenia: It is characterized by (1) distorted thoughts, (2) laughing or crying at completely inappropriate times, (3) often disturbed emotions with rapid shifts from one extreme response to other, and (4) incoherent and bizarre behavior lasting for a week or more. Schizophrenics may also suffer from delusions, auditory hallucinations, and may find difficulty in handling even the simplest jobs.
  • Borderline personality disorder (BPD): This disorder is an emotionally unstable personality disorder which is characterized by impulsivity, unpredictable moods, outbursts of emotion, behavioral explosions, quarrelsome behavior, and conflicts with others. BPD can be diagnosed with specific patterns of behavioral, emotional, and cognitive instability and dysregulations. These individuals are highly reactive and, generally, experience episodic depression, anxiety, and irritability. They also have problems with anger and anger expression. Relationships with other individuals are chaotic, intense but, nevertheless, hard to give up. Individuals with BPD often attempt to injure, multilate, or kill themselves, and have little sense of self since they feel empty.

Drugs and Alcohol Abuse

• Surveys and statistics show that the use of drugs and alcohol has been on the rise especially among the youth.
• This is really a cause of concern as it can result in many harmful effects.
• Proper education and guidance would enable youth to safeguard themselves against these dangerous behav- ior patterns and follow healthy lifestyles.
• Drugs that are commonly abused are opioids, cannabinoids, and coca alkaloids. The majority of these are obtained from flowering plants. Some are obtained from fungi.

Addictive Disorders

• If the body needs continuous presence of psychoactive substance within it, it is called addiction.
• Psychoactive drugs have the ability to alter the activity of nervous system.
• Different psychoactive drugs along with their category and effects are given in Table 8.5.

• If a person who is a habitual user abstains from a drug (abstinence), his body reacts, i.e., ceases to function normally. It is called physical dependence.
• The symptoms appearing in the body are withdrawal symptoms and range from mild tremors to convulsions, abdominal pain, diarrhea, and muscle cramps, all depending upon the type of drug abused.
• In many cases, the withdrawal symptoms may be life threatening and may need medical supervision.

Sedative-Hypnotics

• Sedatives are drugs that reduce excitement, assuage pain, and lower the physiological or functional activity leading to drowsiness or sleep.
• Hypnotics are also the drugs that induce sleep.
• Sedative-hypnotics are more or less general CNS (central nervous system) depressants. These include barbiturates and benzodiazepines.
• Barbiturates and benzodiazepines
  • These are substituted derivatives of barbituric acid (a combination of melonic acid and urea, called malonyl urea) which are general depressants of all excitable cells but CNS is the most sensitive to them.
  • These reduce anxiety and induce sleep. Their repeated use causes addiction.
  • It results in permanent damage to brain, headache, coma, and muscular twitching.
  • Sudden withdrawal causes epilepsy.

Opiates (Opioid Analgesics or Opiate Narcotics)

• Opiates or opioids are derived from opium along with their synthetic relatives.
• Drugs that relieve pain by acting on CNS are termed as analgesics. They are also called painkillers.
• Opium is the dried latex of unripe capsular fruits of poppy plant, Papaver somniferum (family Papaveraceae).

• It has heavy smell and bitter taste.
• It is smoked or eaten.
• Opioids bind to specific opioid receptors present in our CNS and gastrointestinal tract.
• Opiates have narcotic, analgesic, sedative, and astringent (that cause contraction of body parts) effects.
• They slow down respiratory activity, cause constriction of pupil of eye, decrease glandular secretions, impair digestion, and produce nausea, vomiting, and sterility.
• Opium addicts lose weight, fertility, and interest in work.

• Opium contains a number of alkaloids:
  • Morphine: Serturner, a pharmacist, isolated the active principal of opium in 1806 and named it “morphine.” It is the main opium alkaloid. It is a strong analgesic and also has sedative and calming effect. Morphine depresses respiratory center and contributes to the fall in SP. It can cause bradycardia (slow heart beat), release of ADH, reduction in urine output, constipation, mild hyperglycaemia, etc. It causes addiction. Diacetyl- morphine hydrochloride is brown sugar/smack and is a more powerful analgesic than morphine.

• • Codeine: It is a derivative of opium (methylmorphine) which occurs naturally in opium and is partly converted in the body to morphine. It is a mild analgesic, which does not cause addiction. It is an ingredient of many medicines and cough syrups. Its prominent side effect is constipation.
  • Heroin (diamorphine or diacetylmorphine): Heroin, also called as smack, is a semi-synthetic opiate which is addictive and most dangerous of all opiates. It is about three times more potent than morphine. Due to its high potency, it has been favored in illicit drug trafficking; so, it has been banned in most countries. Heroin is formed from morphine by acetylation. It is taken orally or inhaled or injected; pure drug is seldom taken. It induces drowsiness and lethargy. Heroin causes indigestion, reduced vision, decreased weight, sterility, and total loss of interest in work. Since heroin addicts are careless about syringes and needles for injection, this may cause blood poisoning, abscess formation, hepatitis-S, and AIDS. Withdrawal symptoms are unpleasant which include vomiting, diarrhea, shivering, running nose, muscular and abdominal cramps, and epilepsy.
  • Pethidine (meperidine): It is a synthetic opiate which is chemically unrelated to morphine but has many similar actions. Its analgesic efficiency is almost similar to morphine and is more than that of codeine. It is equally sedative and euphoriant. It causes less histamine release and is safer in asthmatics. It has local anesthetic action. It is mostly metabolized in liver.
  • Methadone: It is a synthetic opiate which is chemically dissimilar but pharmacologically very similar to morphine. It has analgesic, respiratory depressant, and constipating actions similar to morphine. Withdrawal symptoms are gradual and less severe.

Stimulants

• Drugs which stimulate the nervous system; make a person more wakeful, alert, and active; and cause excitement are termed as stimulants.
• However, addiction is psychological and the withdrawal of stimulant is followed by depression, anxiety, and restlessness. For example, caffeine, cocaine, amphetamines, etc.
  • Caffeine
    • It is bitter alkaloid obtained from the leaves of tea plant (Thea sinensis), seeds of coffee plant (Coftea arabica), and seeds of cocoa plant (Theobroma cacao). It is a mild stimulant and is taken as beverages (tea, coffee, cocoa, and cola drinks).
    • Caffeine is CNS stimulant which provides a sense of well-being and alertness. It beats boredom, improves performance, and also acts as cardiac and respiratory stimulant; thinking becomes clear after its intake.
    • It is mild diuretic (increases urine output).
    • Caffeine increases contractile power of skeletal muscles.
    • It inhibits the release of histamine.
    • Higher doses of caffeine cause nervousness, restlessness, panic, insomnia (lack of sleep), and excitement.
    • Excessive intake of caffeine also causes addiction and indigestion and disturbs renal functions.
  • Cocaine
    • It is a natural alkaloid obtained from the leaves of coca plant, Erythroxylum coca (family Erythroxylaceae).
    • It is bitter, white, crystalline powder with vasoconstrictor properties and, hence, is a good local anesthetic.
    • It interferes with the transport of neuro-transmitter dopamine.
    • It is taken by snorting.
    • It is a powerful CNS stimulant which induces a sense of well-being or euphoria and pleas- ure and delays fatigue.
    • It also increases heart beat, blood pressure, and body temperature.
    • It is smoked or injected or inhaled by addicts.
    • It causes lack of sleep, loss of appetite, head- ache, convulsions, insomnia, and respiratory or cardiac failure, and may lead to mental disorder.
    • Excessive dosage of cocaine causes hallucinations. Some other plants such as Atropa bellandona and Datura have hallucinogenic properties.

• • Amphetamines
    • These are synthetic drugs, commonly called pep pills, anti-sleep drugs, or speed uppers because they are CNS stimulants. These cause alertness, self-confidence, talkativeness, and increased work capacity.
    • These stimulate respiratory center and cause wakefulness and postponement of sleep and, hence, are called anti-sleep drugs.
    • Due to slow metabolism, the drug is found in urine for several subsequent days.
    • It is one of the drugs included in the “dope test” for athletes. It suppresses hunger (anorexia) and causes addiction.
    • High doses of amphetamines produce euphoria, marked excitement, sleeplessness, nausea, and vomiting.

Psychedelic Drugs (Hallucinogens)

• The drugs that change one’s mood, behavior, thoughts, and perceptions in a manner like that seen in psychosis are termed as psychedelic drugs.
• These cause hallucinations and usually make users see colors and hear sound. Hallucinogens generally produce a dream-like state by disorientation and loss of contact with reality without any true sensory stimulus.
• These are called vision-producing drugs as these pro- duce false imaginations or extreme feeling of either despair or euphoria by effecting cerebrum and sense organs.
  • LSD (lysergic acid diethylamide): It is the most powerful psychedelic (hallucinogen). It is a crystalline amidated alkaloid obtained from ergot of fungus Claviceps purpurea that is a parasite on rye plant. LSD was synthesized by Hofmann (1938). It causes horrible dreams, emotional outbursts, hallucination, chronic psychosis, and severe damage to the CNS. LSD also brings about chromosomal and fetal abnormalities.
  • Mescaline: It is a white powdery alkaloid, obtained from the tops (called mescals) of a small spineless cactus, Lophophora williamsii. This cactus is also called Peyote cactus. It is a low- potency hallucinogen.
  • Psilocybin: It is obtained from the fruiting bodies of Mexican mushroom (fungus), Psilocybe mexicana (family: Agaricaceae). Psilocybin is a crystalline solid that may have value in psychological medicine. Its effects are similar to those of mescaline.
  • PCP (phencyclidine piperidine): It has stimulant, depressant, hallucinogenic, and analgesic properties. Its higher dose may produce hypersalivation, vomiting, fever, and even coma. It is widely used in veterinary medicine to briefly immobilize large animals.
    Synthetic derivatives such as DMT (dimethyl- tryptamine), DOM (dimethoxymethylamphetamine), and DMA (dimethoxyamphetamine) are also hallucinogenics.
  • Products of hemp plant: Known as cannabinoids, tetrahydrocannabinol (THC) is present in hemp plant, Cannabis (family: Cannabinaceae). Bhang, ganja, marijuana, etc., are the various forms in which THC is used as hallucinogen.

• • • Bhang: It is obtained from the fresh/dried leaves and flowering shoots of both male and female plants of Cannabis sativa. Bhang is generally taken orally (e.g., in the form of drink or pakora or tikki). It acts slowly.
    • Ganja: It is the dried unfertilized female in- florescence of Cannabis sativa. It is smoked generally in cigarettes. It is more potent, and its effects are produced almost instantaneously.
    • Charas: It is the dried resinous extract from the flowering tops and leaves of Cannabis sativa. It is most potent and smoked with tobacco. In some countries like America, charas is called hashish. Liquid hashish is called hash oil, which may contain a THC concentration of 25-60%.
    • Marijuana: It is obtained from the dried flowers and top leaves of the female plants of Cannabis sativa. Its most active ingredient is delta-9-tetrahydrocannabinol (delta-9 THC). It is smoked in cigarettes.

Alcoholism

Alcoholism is the dependency of a person on regular consumption of alcohol either in low concentration (wine, bear, etc.) or in high concentration (rum, vodka, etc.).

Effects of Alcohol on an Individual

• Effect on liver
  • Absorbed alcohol is carried directly to the liver, where it becomes the preferred fuel.
  • Use of moderate amounts of alcohol does not cause liver damage, provided adequate nutrition is maintained.
  • However, chronic alcoholism causes the following diseases.
    • Alcoholic fatty liver: The liver becomes enlarged, yellow, greasy, and firm. Hepatocytes (cells of liver) are distended by large fat globules which push the hepatocyte nucleus against the cell membrane. There is increase in fat synthesis in the liver.
    • Alcoholic hepatitis: It is characterized by the degeneration of hepatocytes. The damaged (degenerated) hepatocytes are surrounded by polymorphonuclear leucocytes. These hepatocytes may be pale and swollen. Some contain dense eosinophilic masses called Mallory’s hyaline.
    • Alcoholic cirrhosis: With continued alcohol intake, there is destruction of hepatocytes and fibroblasts (cells which form fibers) and stimulation of collagen protein formation.
    • Cholestasis (Gr. chole-bile, stasis-standing still): It is stoppage in the flow of bile. It is characterized by jaundice, abdominal pain, and hepatomegaly (enlargement of liver).
• Effect on nervous system: These are characterized as follows:
  • Will power, judgment power, and self control become reduced.
  • Control on emotion reduces.
  • Moral sense reduces.
  • Cerebellum becomes affected which results in the loss of muscle coordination. So affected person shows staggering gait and incoherent speech.
  • Inflammation of axons of neurons leads to neuritis.
• Effects on stomach:
  • High doses of alcohol cause ill effect on the gastric glands of stomach. These glands secrete gastric juices in excess which cause inflammation to gastric mucosa.
  • This condition is known as gastritis.
  • It may also result in gastric carcinoma and peptic ulcer.
  • Dilute alcohol (optimum 10%) stimulates gastric secretion (specially acid).
  • Acute alcoholic intake can result in the inflammation of the oesophagus (oesophagitis) and stomach (gastritis).
  • Chronic heavy drinking, if associated with violet vomiting, can produce a longitudinal tear in the mucosa at the gastrointestinal junction Mal- lory-Weiss syndrome (also called Mallory-Weiss Lesion).
• Effect on heart: Due to the deposition of alcoholic fat on the wall of blood vessels, the lumen of blood vessels becomes reduced. This increases the blood pressure and, hence, the activity of heart. The size of RBCs becomes increased but the number of RBCs, WBCs, and platelets is reduced.
• Effect on kidneys: Alcohol reduces the release of hormone ADH (antidiuretic hormone) due to which excess amount of water is released from the body. So, alcoholism greatly causes dehydration condition.
• Heavy drinking can cause an acute alcoholic myopathy characterized by painful and swollen muscles and high levels of serum creatine phosphokinase (CK).
• Alcohol increases RBC size causing mild anemia. Chronic heavy drinking can also decrease the production of WBCs. Alcohol may decrease platelet aggregation.
• Effects on the skeletal system include alternations in calcium metabolism with an increased risk for fracture and osteonecrosis (death of bone mass) of the head of femur.
• Hormonal changes include an increase in cortisol levels, inhibition of vasopressin, reversible decrease in serum thyroxine, and a more marked decrease in serum triiodothyronine (T3).
• Heavy drinking during pregnancy results in serious consequences for fetal development. The fetal alcohol syndrome (FAS) includes facial changes, poorly formed concha (cavity of pinna), small teeth with faulty enamel, and defects in atria and ventricles of heart.
• Regular intake of small to moderate amounts has been found to raise HDL or high density lipoproteins (good cholesterol) and lower LDL or low density lipoproteins (bad cholesterol) levels in the blood plasma. This may be responsible for the lower incidence of coronary artery disease in such persons. Alcohol also reduces blood sugar level which is harmful for the functioning of brain.
• Effect on immunity: Alcoholism reduces resistance to infection. Alcoholics in most cases are victims of malnutrition and are easily susceptible to diseases like pneumonia.
• Effect on family: The habit of drinking not only creates problems for the drinker but directly or indirectly affects the family and community life. Most drinkers do not think regarding the needs of their children and other members of the family.
• Effect on society: Alcoholism is invariably associated with social crimes and dissolution of moral and cultural inhibitions. Violence and other corrupt practices in the community are often directly or indirectly due to the drinking of alcohol.

Metabolism of Alcohol

• In body, the alcohol passes to the stomach.
• Some amount of it also passes to the proximal part of intestine.
• Thus, stomach and proximal part of intestine absorb this alcohol and then transfer it to blood and from blood to liver.
• In liver, alcohol is converted to acetaldehyde with the help of enzyme alcohol dehydrogenase.
• Acetaldehyde is oxidized by enzyme acetaldehyde dehydrogenase,
• It liberates heat.
• This heat is utilized in the synthesis of fat.
• The excess of fat reduces the formation of glycogen, enzymes, and structural proteins.
• This condition is known as cirrhosis.

Tobacco Addiction

• Tobacco can be obtained from dried and cured leaves of young branches of two species of tobacco plant: Nicotiana tobaccum and N. rustica. Tobacco plant belongs to angiospermic family Solanaceae.
• The use of tobacco started in America where Red Indians started using it. It spread to Europe and other countries in early 1700s.

Tobacco Smoking and Diseases

• Cancer: About 90% victims of lung cancers are associated with smoking. Another cancer is mouth cancer due to chewing of tobacco.
• Immunity becomes weak due to regular use of tobacco.
• The use of tobacco increases male infertility.
• More adrenaline is released which increases blood pressure and heart rate. It may lead to cardiovascular diseases.
• In pregnant women, nicotine alkaloid reduces fetal growth and development.
• Carbon monoxide present in smoke combines with hemoglobin present in blood and forms carboxyhemoglobin. It greatly reduces the oxygen-carrying capacity of blood.
• Premature wrinkling may be possible.
• It is also known to cause pulmonary tuberculosis.
• Smoking causes inflammation of lung alveoli which decreases surface area for gaseous exchange and causes emphysema.
• Smoking causes irritation and inflammation of the mucosa of throat and bronchi, which causes coughing and bronchitis, respectively.
• Smoking accelerates the secretion of gastric juices, which causes gastric and duodenal ulcers.

Drugs of abuse are frequently taken with alcohol or other common medicines, e.g., aspirin and insulin. Such combination can lead to increased sedation or reduced effect of medicine or complication like hypertension.

• Drugs such as barbiturates, amphetamines, benzodiazepines, lysergic acid diethyl amides (LSD), and other similar drugs, which are normally used as medicines to help patients cope with mental illnesses such as depression and insomnia, are often abused.
• Morphine is a very effective sedative and painkiller. It is very useful in patients who have undergone surgery.
• Several plants, fruits, and seeds having hallucinogenic properties have been used for hundreds of years in folk-medicine, religious ceremonies, and rituals all over the globe.
• When these are taken for a purpose other than medicinal use or in amounts/frequency that impairs one’s physical, physiological, or psychological functions, it constitutes drug abuse.
• Drug abuse is found only with those who live a stressful life, unsatisfied with themselves, and feel insecure.
• As problems and stress are becoming a part of modern life, a person must learn to face them.
• One must discuss the problems with family members/ friends and attempt to sort them out, rather than to resort to drug/alcohol use.

Assertion-Reasoning Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).

1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark
3. If Assertion is true but Reason is false, then mark (3).
4. If both Assertion and Reason are false, then mark (4).

Question 1. Assertion: Live attenuated vaccine is better in terms of immunity provided to the recipient.

Reason: As secondary lymphoid organs, example Peyer’s patches, are stimulated to protect the society.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 2. Assertion: Asthma patients must never be exposed to dust.

Reason: Allergic response may cause vasoconstriction and death.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 3. Assertion: Colostrum is a very efficient means of transferring immunity to a newborn.

Reason: IgM from mother’s milk protects the baby from the respiratory infection usually affecting in young age.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 4. Assertion: Vaccine against AIDS has not been made in spite of repeated attempts.

Reason: HIV has the ability to get mutated to form everal subtypes.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 5. Assertion: Antibiotics such as penicillin can be used to treat common cold.

Reason: Penicillin causes lysis of viral cells.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 6. Assertion: SCID is a primary immunodeficiency.

Reason: It is a serious congenital immunodeficiency.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 7. Assertion: AIDS spreads by contact between the blood of an infected person and a healthy person.

Reason: AIDS manifests as tumors or as pathogenic infections.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 8. Assertion: Syphilis spreads by sexual intercourse with infected persons.

Reason: Syphilis is caused by Spirochaete bacterium, Treponema pallidum.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 9. Assertion: All types of cancer result in tumors.

Reason: Cancer is easily treatable with antibiotics.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 10. Assertion: Mother can pass on syphilis bacteria to the developing fetus.

Reason: Placenta in the later part of pregnancy becomes permeable to some pathogens.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 11. Assertion: UV rays are carcinogenic in nature.

Reason: UV rays rupture DNA strands and induce mutations to cause cancers.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 12. Assertion: Metastatic cancers are more serious.

Reason: These spread from one organ to other body organs and there is increased interference with metabolic functioning.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).

Question 13. Assertion: Alcohol is called a stimulant.

Reason: Alcohol is immediately oxidized to produce large amount of energy which increases the activities of CNS.

Answer. 4. If both Assertion and Reason are false, then mark (4).

Question 14. Assertion: Sedatives are used in sleeping pills.

Reason: Sedatives contain opiates which reduce tension and anxiety.

Answer. 3. If Assertion is true but Reason is false, then mark (3).

Question 15. Assertion: Heroin addicts have more chances of occurrence of AIDS, hepatitis, etc.

Reason: Heroin is the most dangerous and addictive opiate.

Answer. 2. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).

Question 16. Assertion: The Widal test is commonly used for the detection of typhoid fever.

Reason: The presence of specific agglutinins in the patients’ blood indicates the presence of typhoid bacteria.

Answer. 1. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).