NEET Biology Revision Notes

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.

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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).

Respiration In Plants

Cellular Respiration

Cellular respiration (the term given by Dutrochet) is essentially a catabolic process, that involves the biological oxidation of organic molecules, and results in the release of energy in the form of ATP. ATP (adenosine triphosphate) is a derivative of AMP (adenosine monophosphate) to which two additional phosphate groups are attached through an anhydride linkage. The two bonds are indicated by the symbol (-). When the first high-energy phosphate bond is hydrolyzed, 8.9 kcal of energy is released.

• When the second phosphate bond is broken, 6.5 kcal of energy is released. However, if the third phosphate group (i.e., of AMP) is hydrolyzed, only 3.4 kcal of energy is liberated. The energy released by the breaking down of phosphate groups in ATP and ADP (adenosine diphosphate) is much more than the energy released on the hydrolysis of most of the other covalent bonds.
• ATP is an instant source of energy within the cell. It is mobile and transports chemical energy to the energy-requiring processes within the cell. Since ATP is found in all living cells, it is called the “universal enemy carrier” or “energy currency” of cells.

Aerobic Respiration

Aerobic respiration takes place in the presence of oxygen. Complete oxidation of the substrate results in the formation of CO₂ and water accompanied by the release of energy, for example, In most forms of life, respiration occurs aerobically.

Anaerobic Respiration

Anaerobic respiration takes place in the absence of oxygen and results in incomplete degradation of the substrate to CO₂ and organic compounds such as ethyl alcohol, lactic acid, etc., accompanied by the release of some energy. Water is not a product of this reaction.

• Usually, anaerobic respiration occurs in the deep-seated tissues of plants and animals, in germinating seeds, in fruits, and among many microorganisms, for example, yeasts and bacteria.
• A large variety of organisms (anaerobic) employ anaerobic respiration as their major energy-yielding process. Some bacteria are even killed if exposed to a substantial amount of oxygen. These are termed obligate anaerobes. The organisms which can respire both in the presence and absence of oxygen are called facultative anaerobes.

Read and Learn More NEET Biology Notes

Respiratory Quotient

Respiratory quotient (RQ) is the ratio of CO₂ volume released to oxygen volume absorbed during respiration and is written as:

• The value of RQ varies with the substrate. Thus, the measurement of RQ gives some idea about the nature of the substrate being respired in a particular tissue. The value of RQ is usually measured by Ganong’s respirometer.
• When carbohydrates act as respiration substrates (germinating wheat, oats, barley, paddy grains, green leaves kept in the dark, tubers, rhizomes, etc.).

When fats act as respiratory substrate (germinating castor, mustard, linseed, til seeds, etc.): Fats are poorer in O₂.

When proteins act as respiratory substrates (germinating gram, pea, bean, mung seeds, etc.). The value of RQ is less than unity (0.5- 0.9): Proteins are also poor in O₂. When an organic acid acts as a respiratory substrate: Organic acids are rich in O₂.

Incomplete oxidation of carbohydrates occurs during the night when stomata are open.

In the absence of O₂ (anaerobic respiration).

RQ of maturing fatty seed is greater than 1.  The RQ of a mixed diet is 0.85. The RQ of starved leaves is less than 1. The RQ of colored petals is less than 1.

Glycolysis Or Emp Pathway

In aerobic as well as anaerobic respiration, the initial sequence of events is the same, collectively tanned as glycolysis. Glycolysis (splitting of sugar) results in the breakdown of one molecule of glucose into two molecules of pyruvic acid. It is completed in the cytoplasm of the living cells, not in the mitochondria, and also does not require the presence of oxygen. It is also known as the Embden Meyerhof Pamas (EMP) pathway after the names of three German scientists who discovered it.

• The first half of this pathway activates glucose (glucose activation phase; The second half extracts the energy (energy extraction phase). Glycolysis yields only 5% of the total ATP production and 2% of the total energy content of glucose.
• All the reactions of EMF are reversible except for those catalyzed by hexokinase, phosphofructokinase, and pyruvate kinase. Nearly all enzymes require Mg²⁺ as a cofactor. The brain, retina, skin, and gastrointestinal tract derive most of their energy from glycolysis. It is the only source of energy in RBC.

Reactants Used And The End Products During Glycolysis:

Fate Of Pyruvic Acid

In aerobic oxidation, each pyruvic acid molecule enters mitochondria where its oxidation is completed. It is carried out in the following phases: oxidative decarboxylation (formation of acetyl CoA) and Krebs cycle.

Oxidative Decarboxylation (Formation of Acetyl Coenzyme A)

• Pyruvic acid molecules produced during glycolysis move into the mitochondria and all reactions of cellular respiration take place within these tiny powerhouses. Here each three-carbon molecule of pyruvic acid is decarboxylated (i.e., CO₂ is released) and dehydrogenated (i.e., hydrogen atoms are removed).
• Due to the release of CO₂, the three-carbon molecule of pyruvic acid is converted to a two-carbon acetyl group which reacts with a large complex coenzyme called coenzyme A. This results in the formation of a compound called acetyl coenzyme A.
• This process requires five cofactors, namely, Mg⁺⁺, thiamine pyrophosphate (TPP), NAD, coenzyme A, lipoic acid, and a huge enzymatic complex of three enzymes called pyruvate dehydrogenase

Acetyl coenzyme A is often called the substrate entrant of the TCA cycle and is a link between glycolysis and the TCA cycle. It is also linked with fat metabolism.

TCA Cycle (Krebs Cycle Or Citric Acid Cycle): The reactions of this cycle were worked out by Sir Hans Adolf Krebs in the flight muscles of pigeons. In these reactions, hydrogen atoms are removed from acetyl CoA and transferred to coenzymes for further processing in the electron transport system.

• The cycle is called the citric acid cycle (because of the formation of citric acid in the first step in this cycle) or the TCA cycle (tricarboxylic acid cycle, because many intermediate compounds formed in the cycle have three carboxyl groups).
• The reactions of the Krebs cycle require the presence of oxygen and are confined to the mitochondrial matrix. This cycle serves as a common oxidative pathway for carbohydrates, fats, and proteins.
• All enzymes are soluble in the mitochondrial matrix but succinate dehydrogenase is found attached to the inner mitochondrial membrane. One molecule of ATP (via GTP), three NADH₂, one FADH₂, and two molecules of CO₂ are released per molecule of costly CoA oxidized; however, as two molecules of pyruvic acid are formed from one glucose molecule, the TCA cycle must occur twice for each molecule of glucose respired.
• Therefore, two ATP, six NADH₂, and two FADH₂ are formed from two molecules of acetyl CoA (coming from one molecule of glucose). Some intermediates of the cycle are moreover used in synthesizing important biomolecules such as glutamate and aspartate. Krebs cycle involves a total of nine steps. The reactants and products per acetyl coenzyme A in the Krebs cycle.

Reactants used and end products in the Krebs cycle:

The TCA cycle has both catabolic and anabolic pathways (amphibolic). Various intermediates of the cycle are precursors of various compounds, for example.

• Acetyl CoA → Raw material for carotenoids, terpenes, gibberellins, etc.
• Succinyl CoA → Raw material for chlorophyll, cytochromes
• Oxaloacetic Acid → Raw material for alkaloids, pyrimidines

Electron Transport System

Reduced coenzymes (NADH₂, FADH₂,) generated in glycolysis (2 NADH₂), oxidative decarboxylation (2 NADH₂), and TCA cycle (6 NADH₂, 2 FADH₂) are transferred to the electron transport system (ETS) embedded in the inner mitochondrial membrane.

• They are oxidized in the presence of O₂ liberating energy and regenerating NAD and FAD. ETS comprises several electron-carrying proteins divisible into five multiprotein complexes. Four of these complexes are concerned with electron transfer while the fifth complex is concerned with ATP synthesis.

ETS has seven electrons and an H⁺ carrier, viz., FAD, FMN, CoQ, cyt b, cyt c, cyt a, and cyt a₃. Two mobile electron carriers CoQ and cyt c. These complexes are:

1. NADH-dehydrogenase complex: Have prosthetic group FMN, FeS.
2. Succinate dehydrogenase complex: Have prosthetic group FAD, FeS
3. Cyt c-reductase complex: Have cyt b, c
4. Cyt c-oxidase complex: Have cyt a Cu_a, Cu_b, cyt a₃.
5. ATPase (F₀-F₁ particle).

Electron and Proton Flow in ETS

O₂ reacts with terminal H⁺ and finally, e^– acceptor in ETS to form metabolic water. Reduced coenzyme NADH₂ helps in pushing three pairs of H⁺ to the outer chamber of mitochondria while FADH₂ sends two pairs of HT to the outer chamber.

Oxidative Phosphorylation: It is the synthesis of ATP (from ADP and inorganic phosphate) which occurs with the help of energy obtained from the oxidation of reduced coenzymes formed in cellular respiration. ATP synthesis is explained by the chemi-osmotic theory of Mitchell (1961, Nobel Prize 1978).

• The energy liberated during electron transport is used in building a proton gradient or proton motive force (PMF) in the outer chamber—three pairs of protons during the oxidation of each NADH + H⁺ and two pairs of protons during the oxidation of each FADH₂.
• The inner mitochondrial membrane has F₀-F₁ or ATPase or elementary particles for proton transport. The F₀ parts of elementary particles function as proton tunnels.
• The stalk part of elementary particles has coupling factors while heads have ATPase proper for ATP synthesis.
• Two protons entering an elementary particle knock out one oxygen of inorganic phosphate and convert the latter into energy-rich or active phosphate which combines with ADP to form ATP. The complete oxidation of NADH forms three ATP molecules while one FADH₂ forms two ATP molecules.

Electron Transport System: Reactants And Products:

Pentose Phosphate Pathway

Pentose phosphate pathway (PPP) Warburg-Lipman-Dickens cycle or hexose monophosphate shunt (HMS) is an alternative pathway occurring in cytoplasm and chloroplast in the presence of O₂ and is found both in prokaryotes and eukaryotes. It was first studied by Warburg et al. (1935) and Dickens (1938). It is favored by the presence of NDP. It acts as a safety valve and a shunt to DAP. The important characteristics are:

1. Hexoses are converted to pentoses.
2. Direct oxidation of glucose to CO₂ and H₂O.
3. Synthesis of important intermediates such as NADPH₂, ribose, and erythrose 4-phosphate.
4. Important in tissues such as the liver, ovary, testes, adipose tissue, and germinating seeds.
5. Low activity in skeletal muscles.

In this cycle, out of six glucose 6-phosphate molecules entering, only one is completely oxidized, while the other five are regenerated. The complete degradation of one glucose molecule leads to the formation of 12 molecules of NADPH₂, which ultimately yields 36 ATP molecules, while the net yield is 35 ATP molecules.

Types Of Anaerobic Respiration And Fermentation

Different types of anaerobic respiration and fermentation (also called intramolecular respiration) are as follows:

• Alcoholic fermentation/anaerobic respiration: It is the most common type of fermentation taking place in yeast and bacteria and parts of higher plants. The term fermentation was first of used by Pasteur in 1857 for the alcoholic fermentation of yeast. Buchner (1897) extracted zymase complex enzymes from yeast cells.
• Fermentation takes place in the solution of large numbers of sugar, fructose, galactose, mannose, and disaccharides. In fermentation by yeast, when the percentage of alcohol in the sugar solution is 9-18%, yeast cells are killed, and fermentation stops.
• At the time of germination of seeds, the amount of sugar increases so that fermentation takes place in barley germinating grains. Alcoholic fermentation takes place in two steps. In the first step, pyruvic acid is decarboxylated resulting in the formation of acetaldehyde and CO₂.

Lactic acid fermentation: Pyruvic acid formed at the end of glycolysis is converted to lactic acid by homofermentative lactic acid bacteria (Lactobacillus lactis).

Lactic acid and ethyl alcohol fermentation

Respiratory Inhibitors

Cyanide (CN) and azide (N₃^–) are effective inhibitors of respiration. However, in plants, this effect is minor. The respiration that continues in this situation is called cyanide-resistant respiration.

The reason that respiration can continue in plants, even when cytochrome oxidase is blocked, is that such mitochondria have an alternative route allowing the transport of electrons to oxygen from ubiquinone to a flavoprotein to oxidase. Phosphorylation is coupled to the pathway. Therefore, it leads mainly to the production of other inhibitors, not ATP. Other inhibitors are rotenone, CO, H₂S, barbiturates, malonate, etc.

Respiratory Inhibitors Points To Remember

1. 264 g of CO₂ is liberated during the complete oxidation of 1 80 g of glucose.
2. α-ketoglutaric acid is the first dicarboxylic acid formed during the Krebs cycle.
3. The number of ATP molecules formed by the complete oxidation of pyruvic acid is 15.
4. Mercury is used in anaerobic respiration experiments because it does not react with CO₂.
5. The rate of respiration is measured by a respirometer.
6. Fermentation was discovered by Gay Lussac
7. Fruits and seeds are stored at low temperatures to reduce the rate of respiration.
8. If a leaf is immersed in a sugar solution, the rate of respiration increases.
9. Pasteur effect: A change from anaerobic to aerobic condition decreases the rate of sugar breakdown and CO₂ evolution.
10. Dinitrophenol inhibits ATP synthesis (uncoupler).
11. Oligomycin inhibits oxidative phosphorylation (energy transfer inhibitor).
12. Abnormal rise in the respiratory rate of ripening fruits is called climacteric. For example, bananas.
13. Higher concentrations of CO₂ and the absence of O₂ adversely affect the rate of respiration (except in anaerobic respiration).
14. One molecule of glucose or fructose produces a total of 38 ATP molecules out of which two are used, and therefore, the net gain of ATP is 36. Out of these 38 ATPs, four are formed by direct (substrate) phosphorylation 32 ATPs by oxidative phosphorylation through ETS, and two by GTP.
15. One molecule of NADH₂ forms three ATPs, and one FADH₂ forms two ATPs through ETS.
16. One turn of the Krebs cycle produces 12 ATPs, 11 ATPs through ETS, and one ATP by substrate phosphorylation.
17. ATP formation is an endergonic process and occurs in chloroplast and mitochondria.
18. Muscles get energy by glycolysis.
19. The ratio of CO₂ formation in aerobic and anaerobic respiration is 3:1.
20. The ratio of ATP in aerobic and anaerobic respiration is 18:1.
21. Krebs cycle is basically a catabolic cycle but also functions as an anabolic cycle, hence called an amphibolic cycle. Its starting product is citric acid which is a tricarboxylic acid. It undergoes four oxidations and two decarboxylations to produce CO₂ and H₂O.
22. Cytochromes are Fe⁺²-rich intrinsic proteins and were discovered by MacMunn. Cyt a₃ has both Cu⁺² and Fe⁺² and acts as cytochrome oxidase.
23. Respiration using proteins as substrate is called protoplasmic respiration, while it is called floating respiration when the substrate is carbohydrate or fat.
24. Water produced due to the oxidation of reduced coenzymes with the help of O₂ is called metabolic water.
25. The glyoxylate cycle occurs in seeds that possess tissues rich in fats and enables stored fats to be converted into carbohydrates. Enzymes for the cycle are present in glyoxysomes.

 

Respiration In Plants Assertion-Reasoning Questions

In the following questions, an Assertion (A) is followed by a corresponding Reason (R). Mark the correct answer.

1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
3. If Assertion is true, but Reason is false.
4. If both Assertion and Reason are false.

Question 1.

Assertion: 2,4 DNP is an uncoupling agent in ETS.

Reason: It is soluble in lipids.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 2.

Assertion: Glucose 6-phosphate dehydrogenase deficiency impairs PPP (HMS).

Reason: It is an X-linked recessive disorder.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 3.

Assertion: The RQ of maturing fatty seeds is greater than 1.

Reason: Fats are preferred as energy fuel.

Answer: 3. If Assertion is true, but Reason is false.

Question 4.

Assertion: In cellular respiration, ETS electron movement is a downhill journey.

Reason: Electrons move from high redox potential to low redox potential.

Answer: 3. If Assertion is true, but Reason is false.

Question 5.

Assertion: Succinyl CoA is the precursor of pyrrole group-containing compounds.

Reason: Succinyl CoA is an intermediate of the TCA cycle.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Neural Control And Coordination Introduction

Different activities of an animal’s body are controlled and coordinated through two systems—the nervous system (neural system) and the endocrine system.

Nervous System

The nervous system of all animals is composed of highly specialized cells called neurons, which can detect, receive, and transmit different kinds of stimuli.

• The neural organization is very simple in lower invertebrates. For example, Hydra is composed of a network of neurons.
• The nervous system is better organized in insects, where a brain is present along with the number of ganglia and neural tissues.
• The vertebrates have a more developed neural system.
• The human nervous system is divided into two parts: The central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS includes the brain and spinal cord and is the site of information processing and control.
• The PNS comprises all the body nerves associated with the CNS (brain and spinal cord).
• The nerve fibers of PNS are of two types: afferent- fibers and efferent fibers. Afferent fibers transmit impulses from tissues/organs to the CNS and efferent fibers transmit regulatory impulses from the CNS to concerned peripheral tissues/organs.
• The PNS is divided into two divisions called somatic and autonomic neural systems.
• The somatic neural system relays impulses from the CNS to skeletal muscles while the autonomic neural system transmits impulses from the CNS to involuntary organs and smooth muscles of the body.
• The autonomic neural system is further classified into sympathetic and parasympathetic neural systems.

Types Of Neuron

Nerve cells or neurons are the functional units of the nervous system. These include multipolar nerve cells, with many short dendrites and one long axon (for example, pyramidal cells in the cerebral cortex), bipolar nerve cells, where the long axon extends on either side of the cell body (for example, bipolar neurons in the retina of the eye), and pseudounipolar nerve cells, with cell body on a side-branch of the main axon (for example, cells of dorsal root ganglion).

• Surrounding neurons are special companion cells, known as glia (Gk: glue).
• The glial cells perform many housekeeping functions; astrocytes provide nutritional support to neurons; microglia (phagocytic or scavenger cells) consume waste products.
• Oligodendrocytes insulate by forming myelin sheath in CNG, separating each neuron from others.
• In the PNS, Schwann cells or neurolemmocytes, a type of glial cell, wrap around the axons of neurons, thereby covering the axon with concentric layers of insulating plasma membrane, i.e., the myelin sheath.

Read and Learn More NEET Biology Notes

Nerve Impulse And Its Transmission

Nerve cells have polarized membranes, i.e., they have electrical potential difference or membrane potential. This is because of a variety of ion channels (pores formed by proteins) specific to a particular type of ion.

• Some ion channels remain open while most of them open under one condition and close under another condition.
• Because of such regulated or voltage-gated channels, membranes become excitable as these channels respond to different types of stimuli, for example, light, touch, sound, etc.
• When a neuron is not sending any signal, it is said to be at rest and its membrane has resting membrane potential.

Resting Membrane Potential: In a resting nerve fiber, the cytoplasm just beneath its membrane is electronegative relative to the layer of extracellular fluid (ECF) just outside the membrane.

If the two sides of the membrane are connected by a galvanometer (double beam cathode ray oscilloscope), the inner side is seen to possess a negative potential of about 70 mV relative to the outer side. This is called the resting membrane potential. This results from two factors:

Epithelium

1. The resting membrane has a poor permeability for Na% although it has a higher permeability for K⁺. Therefore, K⁺ can cross more easily while Cl^– and Na⁺ have more difficulty in crossing.
2. A negatively charged protein molecule inside the neuron cannot cross the plasma membrane because of its semipermeability.

• The differential flow of the positively charged ions and the fact that the negatively charged organic ions within the nerve fiber cannot pass out cause an increasing positive charge on the outer side of the membrane and a negative charge on the inner side of the membrane.
• This makes the membrane of the resting nerve fiber polarized (i.e., its outer side is positively charged with respect to its inner side). Such electrochemical gradients are maintained by the active transport of ions involving the Na⁺-K⁺ ion transmembrane pump. It pumps out 3Na⁺ for every 2K⁺ ions passed inwardly.
• K⁺ concentration is 30 times more inside a neuron than outside and Na⁺ concentration is 10 times more in interstitial fluid as compared to the inner side of neuron.

Conduction of Nerve Impulse: It involves initiation of the impulse followed by conduction along the axon to be transferred to the target muscle/tissue.

Initiation of Impulse: When stimulated, voltage-gated Na⁺ channels open which causes a rapid, very localized, temporary inflow of Na⁺ into the cell, which further causes the development of the net positive charge on the inner side of the membrane in that area.

• This is called depolarization. It occurs at a particular region of the neuron called the trigger zone. Voltage-gated ion channels are clustered in the area of the trigger zone.
• The stimulus of the threshold value causes the stoppage of the Na⁺-K⁺ ATPase pump.
• Continued passage of Na⁺ ions into the neuron creates a reverse potential of +20 mV to +30 mV, rarely to +60 mV.
• The total change occurs in a spike-like fashion which is also called spike potential.
• Na⁺ ion channels open for about 0.5 ms. This creates a potential that sets in a wave of depolarization through the nerve fiber.

• The membrane potential that sets in a wave of depolarization is called action potential.
• For most excitable cells, the threshold is about -55 mV to -60 mV.

Conduction Of Impulse: In the area of depolarization, the potential difference across the membrane is small while its nearby region has a large difference in membrane potential. This produces a small local current in the area.

• The local current becomes a stimulus and causes the gated Na+ channels of the next region to open and depolarize the area to produce a fresh action potential.
• The process continues till the impulse reaches the end of the neuron.

Repolarization: As Na⁺ channels close, after 0.5 ms, the membrane becomes extra permeable to K⁺ ions due to the opening of the K⁺ ion gates.

• With the pumping out of K⁺ ions, the neuron interior becomes negative and the potential falls back to the resting potential.
• The phenomenon of change of membrane potential from an excited state to a resting state is called repolarization. However, K⁺ ion channels remain open for a bit longer period so that the membrane potential becomes more negative than -70 mV. This is called hyperpolarization.
• It takes about 1-5 ms for repolarization.

Difference between non-myelinated and myelinated fibers:

Synaptic Transmission

Synapses are the neuronal junctions through which information from one neuron can pass to the other. There are mainly two types of synapses depending upon the nature of the transfer of information across the synapse: electrical and chemical.

Electrical Synapses: At an electrical synapse, ionic current spreads directly from one cell to another through gap junctions.

1. Each gap junction contains a hundred or so tubular protein structures called connexons that form a tunnel to connect the cytosol of the two cells. This provides a path for ionic current flow.
2. Gap junctions are common in visceral (single-unit) smooth muscle, cardiac muscle, and a developing embryo.
3. They also occur in the CNS.

Epithelium

Electrical synapses have three obvious advantages:

1. They allow faster communication than do chemical synapses since impulses conduct across gap junctions.
2. They can synchronize the activity of a group of neurons or muscle fibers. The value of synchronized action potentials in the heart or in visceral smooth muscles is to achieve coordinated contraction of these fibers.
3. They may allow two-way transmission of impulses in contrast to chemical synapses, which function as one-way points of communication.

Chemical Synapses: Chemical synapses have a 10-20 nm gap which is too great a distance for such direct electrical coupling.

• Chemical synapses are the most common type of synapses. These consist of a bulbous expansion of a nerve terminal called a synaptic knob lying in close proximity to the membrane of a dendrite or other part of a neuron.
• The cytoplasm of the synaptic knob contains numerous tiny, round sacs, called synaptic vesicles.
• Each vesicle has a diameter of approximately 50 nm and contains as many as 10,000 molecules of a neurotransmitter substance responsible for the transmission of nerve impulses across the synapse.
• The membrane of the synaptic knob on the axon side, thickened as a result of cytoplasmic condensation, is called the presynaptic membrane.
• The mechanism of transmission of nerve impulses through chemical synapse is as follows:

Examples Of Excitatory And Inhibitory Neurotransmitters:

Points To Remember

• Acetylcholinesterase is present in the muscle cell or post-synaptic neuron. It breaks down acetylcholine into acetate and choline and terminates the action of the transmitter.
• Nor-epinephrine secreted by the sympathetic neural system and also by some neurons of the central neural system is inactivated by the enzyme monamine oxidase.

Central Nervous System Of Humans

The structures of the CNS arise from their embryological components.

• Prosencephalon: Becomes thalamus and hypothalamus (diencephalon); cerebral cortex, corpus striatum, hippocampus, and amygdala (telencephalon).
• Mesencephalon: Becomes midbrain.
• Rhombencephalon: Develops into the medulla (myelencephalon) and pons and cerebellum (metencephalon).

Brain

Meninges: The brain is surrounded by three protective coats of connective tissue besides the bony cranium. These are known as meninges (singular, meninx).

1. Pia mater: It is the inner meninx. It is very thin, highly vascular, and closely invests the brain. It is covered by simple squamous epithelium.
2. Arachnoid mater or membrane: It is the middle meninx. It is also thin but is non-vascular. It is covered with simple squamous epithelium on both (internal and external) surfaces. There is a narrow space between the pia mater and the arachnoid membrane. It is called the subarachnoid space. It contains cerebrospinal fluid and is crossed by a number of connective tissue strands.
3. Dura mater: It is the outer meninx. It is thick, and tough, and lines the cranial cavity. Its internal surface is covered with simple squamous epithelium. A very narrow space also exists between the dura mater and the arachnoid membrane. It is called the subdural space. It contains a little fluid which is not the cerebrospinal fluid.

An adult human brain contains more than 100 billion neurons and almost 10 times neuroglia cells. The brain is divided into three main sections: (I) forebrain, midbrain, and hindbrain.

Epithelium

Different Regions of the Brain

Forebrain: It consists of two main parts, cerebrum and diencephalon.

Cerebrum: By far the largest and most highly developed part of the brain is the cerebrum. It is divided into two hemispheres by a prominent longitudinal fissure. The two hemispheres are connected by a bundle of transverse fibers called the corpus callosum. The anterior part of the corpus callosum is curved and is called genu, while the posterior part is called splenium. Each cerebral hemisphere is divided into four lobes. These are frontal at the front, parietal toward the top of the head, temporal on the side, and occipital at the rear.

Cerebral Lobes And Their Major Functions:

Cerebral cortex: The outer surface of the cerebrum, called the cortex, is a layer only 2-4 mm thick.

• Because the six layers are packed with 10 billion pyramidal, spindle, and stellate neurons with a greyish-brown appearance, it is referred to as grey matter.
• The cerebral cortex contains roughly 10% of all neurons of the brain.
• Much of the neural activities occur here, for example, from the touch of a feature to the movement of an arm.
• Unlike the mouse brain, the human brain is greatly convoluted.
• These convolutions or folds consist of sulci (sing, sulcus: small groove), fissures (large grooves), and gyri (sing, gyrus: bulge between adjacent sulci or fissures).

• These greatly enlarge the surface area of the cortex.
• In fact, two-thirds of the surface of the cortex is hidden in sulci and fissures. Thus, their presence triples the area of the cerebral cortex.
• Beneath this run millions of axons comprising nerve fiber tracts, connecting the neurons of the cerebral cortex with those located elsewhere in the brain.
• The large concentration of myelin gives this tissue an opaque white appearance. Hence, they are referred to by the term white matter.
• By examining the effect of injuries or lesions and the effect of electrical stimulation on the behavior, it has been possible to map roughly the location of its various associative activities on the cerebral cortex.
• Each area is referred to as a specialized cortex.
• There are three general kinds of cortex: sensory, motor, and associative.

Diencephalon: The diencephalon contains epithalamus, thalamus, and hypothalamus.

• The epithalamus is a thin, non-nervous roof of the diencephalon.
• Its anterior region is folded and fused with pia mater to form the anterior choroid plexus. This is responsible for the formation of cerebrospinal fluid (CSF).
• Above it is present pineal stalk bearing the pineal body at the top of it.
• The pineal body is an endocrine gland and is also taken as a vestige of the third eye.
• The thalamus directs sensory impulses from the lower parts of the brain and spinal cord to appropriate parts of the cerebrum.
• Limited sensory awareness of pain, temperature, touch, and pressure is provided by the thalamus.

Hypothalamus: As the name implies, the hypothalamus nestles at the base of the thalamus, and so of the brain.

• Although relatively small, just 4 g, about 1/300 of the total brain mass is highly vascularized.
• It integrates and controls visceral activities.
• The hypothalamus, through its connection with the brain stem, maintains homeostasis and the body’s internal equilibrium, specializing in involuntary behavior control.
• The nuclei in it signal the body to eat, drink, get angry, keep cool, etc.
• The hypothalamus organizes behavior related to the survival of species: fighting, feeding, fleeing, and mating.
• It keeps the body temperature at roughly 37°C by means of a complex thermostat system.
• It also influences respiration and heartbeat and sends, out signals to correct them when they are wrong.
• Through connections with the pituitary gland, it controls growth and sexual behavior.

Basal ganglia: The inside of the human brain is not so densely packed, but there are all kinds of different collections of neurons, called nuclei, each with its specific functions.

• These control different body activities automatically.
• Basal ganglia are a collection of subcortical nuclei in the forebrain, at the base of the cortex.
• The largest nucleus in it is the corpus striatum.
• It regulates the planning and execution of stereotyped movements.
• Other basal ganglia perform at a subconscious level learned patterns of movements such as slow and fast pedaling, slow and fast writing/typing, etc.
• Destruction of the dopamine-secreting par compacta part of the basal nucleus called substantia nigra leads to paralysis agitans, Parkinson’s disease. Huntington’s chorea is due to the degeneration of GABA-secreting neurons of the corpus striatum and acetylcholine-secreting neurons of other parts.

Limbic system: Flared like a wishbone, a ring or fork through extensive neural links with the cerebrum and the brain stem below constitute what is called limbic system (meaning lip-like).

• The limbic system sends out signals to the rest of the brain and the body which have a great effect on your behavior.
• It includes the hypothalamus, amygdala, hippocampus, septum, anterior nucleus of the thalamus, and a portion of basal ganglia.

Amygdala: above the hypothalamus, attached to the inner lips of both forks, is like an almond-shaped amygdala. This bulge of neurons is like a defense castle controlling moods, especially anger and rage. Various regions of the amygdala play important roles in emotional behavior such as aggression and remembering fear.

This remarkable organ deals with a strange mix of signals about smells and memories.

The hippocampus functions as a kind of index for the recall of an event with its associated memory.

It converts information from short-term to long-term memory, essential in learning.

The septum linked to the hypothalamus contains yet another emotional center for sexual arousal.

Epithelium

Midhniln: It has two structures: corpora quadrigemina and crura cerebri.

Corpora Quadrigemina: It contains four lobes, therefore, corpora quadrigemina.

• Its principal structures are superior and inferior colliculi.
• The superior pair of colliculi receives sensory impulses from the eyes and muscles of the head and controls visual reflexes. For example, they control and coordinate the movement of the head and eyes, to fix and focus on an object.
• The inferior pair of colliculi receives sensory impulses from the ears and muscles of the head and controls auditory reflexes such as the movement of the head to locate and detect the source of a sound.

Crura cerebri (cerebral peduncle): These are two heavy fibrous tracts on the inferior side of the midbrain and connect the hindbrain with the forebrain.

• Crura cerebri is involved in controlling muscle tone and modifying some motor activities.
• These relay sensory as well as motor impulses between forebrain and hindbrain.

Hindbrain: It consists of the cerebellum, pons, and medulla.

1. Cerebellum
   • To the rear of the brain and placed under the cerebrum, the cerebellum is the second largest part of the brain, which means simply “little cerebrum.
   • Wedged between cerebral hemispheres and the brainstem, the cerebellum is made up of two cerebellar hemispheres.
   • Like the cerebrum, the cerebellum has its grey matter on the outside, comprising three layers of cells and fibers.
   • The middle layer contains characteristically large flask-shaped Ptirkinje cells.
   • Tree-like structure with a myriad of dendrites, Purkinje cells rank among the most complex of all neurons.
   • The white and grey matter form arbor vitae.
   • The central portion of the cerebellum has a worm-like appearance as it is narrow and furrowed. It is called vermis.
   • Three paired bundles of myelinated nerve fibers, called cerebellar peduncles, form communication pathways between the cerebellum and other parts of the CNS.
   • The superior cerebellar peduncles connect the cerebellum to the midbrain, middle cerebellar peduncles communicate with pons, and inferior cerebellar peduncles consist of pathways between the cerebellum and medulla oblongata as well as the spinal cord.
   • The cerebellum does not initiate movement but modulates or reorganizes motor commands.
   • The cerebellum’s unconscious directions and cerebrum’s conscious instructions determine how and when to move body parts.
   • The cerebellum is vital to the control of rapid muscular activities such as running, typing, and even talking.
   • All the activities of the cerebellum are involuntary but may involve learning in their early stages.
2. Pons: Pons (Latin: bridge) forms the floor of the brain stem.
   • It serves as a neuronal link between the cerebral cortex and cerebellum.
   • It has a pneumatic center and a switch-off center for inspiration.
3. Medulla oblongata: Literally meaning oblong mar- mu-, medulla oblongata is the posteriormost part that connects the spinal cord and various parts of the brain.
   • It lies with its breathing center, cardiovascular center, and vomiting center.
   • The Vagus nerve arises from the medulla.
   • Its roof is thin and non-nervous and constitutes posterior choroid plexus.
   • Below the plexus, the roof has three openings, a pair of lateral apertures called foramina Luschka, and a single median foramina Magendie.
   • These apertures connect the external and internal components of the CSF of the brain.
   • Most of the sensory as well as motor nerve tracts cross over to the other side of the medulla. Therefore, the right half of the cerebrum controls the left half of the body and vice versa.

The reticular formation that connects to the thalamus and major nerves in the spinal cord is the gatekeeper to consciousness.

Brain stem: It is the area of the brain between the thalamus and spinal cord and includes the medulla, pons, and midbrain. Diencephalon may or may not be included.

Ventricles of the Brain and Cerebrospinal Fluid:

• The ventricles consist of four hollow, fluid-filled spaces inside the brain.
• A lateral ventricle lies inside each hemisphere of the cerebrum.
• Each lateral ventricle is connected to the third ventricle by an interventricular foramen (foramen of Monro).
• The third ventricle consists of a narrow channel between the hemispheres through the area of the thalamus.
• It is connected by a cerebral aqueduct or aqueduct of Sylvius or iter in the midbrain portion of the brain stem to the fourth ventricle in the pons and medulla.
• The fourth ventricle continues with the central canal of the spinal cord.

• Three openings in the roof of the fourth ventricle, a pair of lateral apertures (foramina or Luschka), and a median aperture (foramen of Magendie) allow CSF to move upward to the subarachnoid space that surrounds the brain and spinal cord.
• The CSF is secreted by the anterior choroid plexus and posterior choroid plexus and is found inside the ventricles of the brain, the central canal of the spinal cord.
• The CSF acts as a shock absorber for the brain and spinal cord and may also contribute to nourishing brain tissue. It contains protein, glucose, chloride, and water.

Spinal Cord: It is an elongated cylindrical structure that lies in the neural canal of the vertebral column and is continued with the medulla oblongata through the foramen magnum to the skull.

• It measures about 45 cm in length.
• It extends down up to the first lumbar vertebra where it tapers to a point called conus modular/conus termi-nalis. However, the meninges of the spinal cord continue as the film terminates starting from the conus and running up to the coccygeal region.
• The spinal cord shows two enlargements: brachial swelling (from 4th cervical to 1st thoracic vertebrae) and lumbar swelling (from 9th thoracic to 12th thoracic vertebrae).
• The spinal cord possesses an anterior and a posterior median fissure running along its length.
• The grey matter of the spinal cord is internal and present around the central canal.
• It is produced into posterior and anterior pairs of grey columns/roots.
• Each dorsal root has a ganglion called dorsal root ganglion.
• The dorsal root is sensory and the ventral root is motor in nature. Both get combined before coming out of the vertebral column through intervertebral foramina.
• The white muter is outer and is divided into four funiculi one dorsal, one ventral, and two lateral
• The spinal cord conducts impulses to and from the brain.
• The dorsal funiculus has an ascending nerve tract for conducting sensor impulses toward the brain.
• Latetal and ventral funiculi conduct motor impulse Hour brain to spinal coni.
• It controls most of the reflex activities.

Peripheral Nervous System Of Humans

The PNS is constituted by the nerves that arise from the brain and spinal cord. They are, respectively, called cranial (cerebral! and spinal nerves, PNS is subdivided into the somatic neural system and the autonomic nervous system.

Cranial nerves:

• There are 12 pairs of cranial nerves in man.
• They leave the cranium through foramina and mainly innervate the head region.
• Their origin, supply, and nature are given in

Origin, Supply, And Nature Of Cranial Name Nerves:

Spinal Nerves:

• In man, there are 31 pairs of spinal nerves. They are classified into live groups.
• They include eight pairs of cervical nerves, 12 pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal.
• They leave the vertebral column through intervertebral foramina, and all of them are mixed. It is divided in the way into three to four branches.
• Posterior or dorsal branch: It supplies muscles and skin of the back.
  • Anterior or ventral branch: It supplies organs in the front and sides of the body. It forms the main spinal nerve.
  • Meningeal or recurrent branch: It supplies meninges, ligaments, blood vessels, and other parts of the vertebral column.
  • Visceral or ramus communicans: It occurs from the first thoracic to third lumbar nerves. It joins the sympathetic chain of its side.
• The main spinal nerves are anterior or ventral branches of spinal nerves joined at places to form plexuses. These plexuses are five in number.
  • Cervical plexus: It occurs in the neck region. The cervical plexus is formed by the first four cervical spinal nerves and the phrenic nerve. The plexus innervates the neck and diaphragm.
  • Brachial plexus: It is formed by the fifth, sixth, seventh, and eighth cervical spinal nerves and the first thoracic spinal nerve. The plexus innervates the chest and arms.
  • Lumbar plexus: It is formed by the first four lumbar spinal nerves. It supplies nerves to the legs.
  • Sacral plexus: The plexus is formed by a branch of each of the fourth and fifth lumbar nerves and the first four sacral nerves. It innervates the hip joint and a part of the pelvis.
  • Coccygeal plexus: It is formed by the fourth and fifth sacral spinal nerves and the coccygeal nerve for innervating skin and parts of the pelvis.

Peripheral Nervous System Of Humans Points To Remember

Spinal accessory (XI) and hypoglossal (XII) are lacking in amniotes (cyclostomes, fishes, and amphibians)

Wrist drop: Due to injury in the brachial plexus.

Foot drop: Due to injury in the sciatic nerve.

Autonomic (or Visceral) Nervous System

The autonomic nervous system consists of two antagonistic components—sympathetic and parasympathetic.

1. Sympathetic nervous system
   • The sympathetic nervous system is represented by a chain of 21 sympathetic ganglia on either side of the spinal cord.
   • It receives preganglionic sympathetic fibers from the spinal cord, which make their exit along with thoracic and lumbar nerves and constitute thoracolumbar outflow.
   • These fibers synapse with the neurons present in the sympathetic ganglia.
   • From the sympathetic ganglia arise postganglionic fibers which terminate on the viscera.
   • Each sympathetic ganglion is connected to the spinal cord by white communicants and the spinal nerve by gray communicants.
   • Some preganglionic fibers pass through the sympathetic chain without synapsing and then join to form splanchnic nerves emanating in some collateral ganglia which include a celiac ganglion, an anterior mesenteric ganglion, and a posterior mesenteric ganglion.
   • The postganglionic fibers arising from collateral ganglia supply the digestive system and urinogenital system.
2. Parasympathetic nervous system
   • It consists of preganglionic parasympathetic fibers, parasympathetic ganglia, and postganglionic parasympathetic fibers.
   • Preganglionic parasympathetic fibers make their exit along with the 3, 4, 9, and 10 cranial nerves, and 2, 3, and 4 sacral nerves.
   • They together form craniosacral outflow.
   • The parasympathetic ganglia do not form any chains and instead lie on or near the viscera.
   • The postganglionic parasympathetic fibers arise from these ganglia and supply the viscera.
   • The neurotransmitter within the ganglion is acetylcholine for both sympathetic and parasympathetic nerves. However, the neurotransmitter between the terminal autonomic neuron axon and the target organ is different in the two antagonistic autonomic nervous systems.
   • In the parasympathetic system, the neurotransmitter at the terminal synapse is acetylcholine, just as it is in the ganglion. In the sympathetic system, the neurotransmitter at the terminal synapse is either adrenaline or noradrenaline, both of which have an effect opposite to that of acetylcholine.
   • There is one exception: the sympathetic postganglionic neuron that terminates on sweat glands uses acetylcholine. Thus, depending on which of the two paths is selected by the CNS, an arriving signal will either stimulate or inhibit the organ. Thus, an organ receiving nerves from both visceral nervous systems is subjected to the effects of two opposing neurotransmitters.
   • If the sympathetic nerve ending excites a particular organ, the parasympathetic usually inhibits it.
   • With few exceptions, organs of the body are innervated by “dual innervations,” and each has a different effect.

• The function of the autonomic nervous system is to control and coordinate the activities of visceral organs. The two components work against one another.
•  The roles of sympathetic and parasympathetic nervous systems are mentioned

Antagonistic Role Of Sympathetic And Parasympathetic Nervous Systems:

Nervous System Points To Remember

1. A gasserian ganglion is associated with the trigeminal nerve.
2. Geniculate ganglion is the swelling of the facial nerve.
3. Parasympathetic fibers do not travel in the dorsal and ventral rami of the spinal nerve.
4. As a result, the effector in the skin, sweat gland, arrector pili muscle, and cutaneous blood vessels receive no parasympathetic innervation.

Reflex Action

Reflex action is the simplest kind of activity which can be defined as an integrated activity occurring involuntarily in response to a stimulus applied to a receptor. The reflex arc is composed of the following: a receptor organ, an afferent neuron, synapse involving some cells in the CNS.

Reflexes can be classified as unconditioned and conditioned reflexes. Unconditioned reflexes are inborn, for example, knee jerk, salivation on tasting the food, peristalsis, and closing of eyes on being approached by an object. Conditioned reflexes are acquired, i.e., developed after birth through conditioning or learning. For example, playing a musical instrument, knitting without looking, writing as well as reading.

Reflexes can also be classified according to the number of synapses in the reflex path. These are as follows:

1. Monosynaptic reflexes: When there is only one synapse in the reflex path. For example, knee jerk.
2. Polysnaptic reflexes: When there is more than one synapse in the reflex path.

Reflex Action Points To Remember

Salivation on seeing hearing or smelling delicious food is an example of cerebral reflex action, whereas withdrawal of legs when a drop of HCl is dropped over the sciatic nerve of a decapitated frog is an example of spinal reflex action.

• Characteristics Of Reflexes: Although the reflexes are involuntary functions, they have certain features that make them highly complicated. Some important characteristics are as follows:
• Predictability: Once the response of an organ to a specific stimulus is observed, one can predict that the same stimulus will always elicit the same response.
• Purposefulness: Generally all reflex actions are useful to the organism and are performed with a definite purpose.
• Localization: In performing a reflex action, a specific effector is involved in response to the stimulus applied to a specific receptor.
• Delay: Reflex time is the interval between the application of the stimulus to a receptor and the beginning of a response by an effector organ. A synaptic delay occurs due to latent period and reflex time at the synapse. This depends upon the number of synapses in the nerve pathway.
• Unlearned: To activate spinal effector mechanisms, no experience is needed to bring them into operation.
• Adjustive and protective: Reflexes serve adjustive and protective purposes and become an important part of animal behavior.
• Fatigue: Reflex responses arc readily fatigued after prolonged and continuous work. As a consequence, the latent period of contraction becomes longer and the rise of tension smaller and more gradual.

Sense Organs

Stimuli are received by certain structures in the body. These are called receptors or sense organs. A receptor may be extremely simple such as those of touch, taste, and smell, or they may be highly complex in their structure as well as working, for example, the sense organs of sight and hearing. Sense organs can be classified based on the following criteria:

1. According to their position
   • Exteroceptors: The external sense organs that receive the stimuli from the outer environment.
   • Proprioceptors: Simple receptors present in joints, skeletal muscles, tendons, etc. They are not in direct contact with the environment but are affected by the changes in the environment.
   • Visceroceptors or internal receptors: The receptors present within the viscera. They receive stimuli originating within the body itself. They are simple and mostly represented by free nerve endings. Perception is conscious awareness and interpretation of sensation.
2. According to the form of stimulus they receive: The sense organs are classified on this basis.

Different Types Of Receptors And The Form Of Stimulus They Receive:

Tangoreceptors: These are the sense organs for touch, pressure, and pain. heat, or cold. They are located in the skin and include:

Meissner’s corpuscles: They are present immediately below the epidermis and receive the stimulus of touch/gentle pressure.

Pacinian corpuscles: Situated deep in the dermis of skin, joints, tendons, and muscles. Each corpuscle has a nerve ending surrounded by connective tissue. They respond to pressure changes.

Merkel’s disc: Occurs in the epidermis and is responsible for touch.

Skin is often called hypothermic because it has more cold receptors. The regulation of temperature in the human body is mediated by the hypothalamus which has a “set point” (96.4°F or 37°C) around which the core temperature oscillates.

Smell Receptors (Olfactoreceptors): The receptors of smell occur in a small patch of olfactory epithelium (pseudostratified epithelium) located in the roof of the nasal cavity. Smell receptors are of the following types:

• Olfactory receptor cells: They act as sensory receptors as well as conducting neurons. The olfactory receptor cells are “unusual” bipolar neurons. Each cell is spindle-shaped and has a thin apical dendrite that terminates in a knob that bears non-motile cilia called olfactory hairs. Olfactory receptor cells are unique in that they are the only neurons that undergo turnover throughout adult life.
• Supporting cells: These are columnar cells that lie between the olfactory receptor cells to support them. They have brownish-yellow pigment (similar to lipofuscin) which gives the olfactory epithelium its yellowish color.
• Basal cells: These are small cells that do not reach the surface. They give rise to new olfactory receptor cells to replace the worn-out ones. This is an exception to the fact that neurons are not formed in the postnatal (after birth) life. The olfactory receptor cells survive only for about two months.
• Olfactory glands (Bowman’s glands): Many olfactory glands occur below the olfactory epithelium that secrete mucus to spread over the epithelium to keep it moist. The mucus also protects the cells from dust and bacteria.
• Working on smell receptors: The dissolved chemicals stimulate the olfactory receptors by binding to protein receptors in the olfactory hairs (cilia) membranes and opening specific Na+ and K channels. This leads ultimately to an action potential that is conducted to the first relay station in the olfactory bulb.

The fibers of the olfactory nerves synapse with mitral cells (second-order neurons) in complex structures called glomeruli (balls of yam). When mitral cells are activated, impulses travel from the olfactory bulbs via olfactory tracts to main destinations (for example, the temporal lobe of the cerebrum).

Sense Organs Points To Remember

1. Women often have a keener sense of smell than men, especially at the time of ovulation.
2. Smoking damages the olfactory receptors.
3. With aging, the sense of smell deteriorates.
4. Hyposmia (hypo: less, osmi: smell) is a reduced ability to smell.
5. In addition to smell receptors, the nose, mouth, and tongue contain a network of nerves that form the trigeminal nerve (fifth cranial nerve) also known as the dentist’s nerve reacts to messages of path,
6. The brain combines the trigeminal signals with those of smell to identify some odors when exposed to irritants such as ammonia or vinegar.
7. The trigeminal can protect by warning about harmful chemicals in the air. Bowman’s glands inside the nose release fluids to get rid of the irritating substances.

Taste Receptors (Gustatoreceptors)

Location: The receptors for taste are found in the taste buds, mostly located on the tongue, but are also found on the palate, pharynx, epiglottis, and even in the proximal part of the esophagus. The number of taste buds declines with age.

Structures: Each taste bud is an oval body consisting of three kinds of cells.

Gustatory receptor cells: They bear at the free end microvilli projecting into the taste pore. The microvilli have special protein receptor sites for taste-producing molecules and come in contact with the food being eaten. Nerve fibers of the cranial nerves 7 (facial),9 (glossopharyngeal), or 10 (vagus) end around the gustatory receptor cells, forming synapses with them. The gustatory receptor cells (taste cells) survive only about 10 days and are then replaced by new cells.

Supporting cells: These cells lie between the gustatory receptor cells in the taste bud. They bear microvilli but lack nerve endings.

Basal Cells: These cells are found at the periphery of the taste bud. They produce supporting cells, which then develop into gustatory receptor cells.

Working: Specific chemicals in solution pass into the taste bud through the taste pore to come in contact with the protein receptor sites on the microvilli of the gustatory receptor cells. The latter set up nerve impulses in the sensory nerve fibers. The nerve fibers transmit the impulses to the taste center in the brain (for example, the parietal lobe of the cerebrum) where the sensation of taste arises.

The facial nerve (8) serves the anterior two-thirds of the tongue, the glossopharyngeal nerve (9) serves the posterior one-third of the tongue and the vagus nerve (10) serves the pharynx and epiglottis but not the tongue.

Organs of Sight (Eye)

Location: The organs of sight in man are a pair of eyes located in the eye orbits of the skull.

Structure: The exposed part of the eye is protected by an upper and a lower eyelid which are provided with eyelashes. Each eye is represented in the form of a spherical eyeball which is moved in the eye orbit with the help of six eye muscles, namely, superior oblique, inferior oblique, superior rectus, inferior rectus, external rectus, and internal rectus. An eyeball measures about 2.5 cm in diameter and is hollow. Its wall is formed of three layers or coats. The outermost is called the fibrous coat, the middle one is a vascular coat, and the inner one is a retina.

1. Fibrous coat: The outer coat of the eyeball is thick and tough. It provides form and shape to the eyeball. The fibrous coat consists of two parts, sclera and cornea.
   • The sclera constitutes about five-sixth of the outer coat. It is white (made up of tough but clastic sheath of fibrous connective tissue containing collagen fibers) and opaque, popularly called white of the eye. Most the of sclera is concealed in the orbit.
   • The cornea is the anterior transparent part of the sclera and constitutes about one-sixth of the fibrous coat, ft is non-vascular and convex anteriorly. The cornea is covered by a thin and transparent membrane called conjunctiva composed of stratified epithelium and continued over the inner surface of lids.
2. Vascular coat: The middle coat of the eyeball is differentiated into three regions, namely, choroid, ciliary body, and iris.
   • The choroid is a delicate, highly vascular, and pigmented part that lies in contact with the sclera. It provides a dark color to the interior of the eyeball, it is black in color. It prevents internally reflected light within the eye. The blood vessels of the choroid nourish the retina.
   • The ciliary body is the part of the vascular coat immediately behind the peripheral margin of the iris. The ciliary body is thicker and less vascular than the choroid. Its inner surface is folded to form ciliary processes. Present within the ciliary body are ciliary muscles.

Iris is the anterior part vascular coat that lies behind the cornea. It is centrally perforated by the pupil, the size of which is regulated by iridial muscles arranged radially and circularly. The iris, being pigmented, provides color to the eye.

Mirror-like tapetum layer of carnivores such as cats, etc.. increases sensitivity by reflecting unabsorbed light through the photoreceptor layer to shine in the dark.

Retina (nervous tunic):

• The third and inner coat of the eyeball, the retina (nervous tunic), lines the posterior three-quarters of the eyeball and is the beginning of the visual pathway.
• The optic disc is the site where the optic nerve exits the eyeball.
• Bundled together with the optic nerve are the central retinal artery, a branch of the ophthalmic artery, and the central retinal vein.
• Branches of the central retinal artery fan out to nourish the anterior surface of the retina.
• The central retinal vein drains blood from the retina through the optic disc.
• The retina consists of a pigment epithelium (nonvisual portion) and a neural portion (visual portion).
• The pigment epithelium is a sheet of melanin-containing epithelial cells that lays between the choroid and the neural portion of the retina some histologists classify it as part of the choroid rather than the retina.
• Melanin in the choroid and pigment epithelium absorbs stray light rays which prevent reflection and scattering of light within the eyeball. This enables the image cast on the retina by the cornea and the lens to remain sharp and clear.
• The pigmented layer is continuous over the choroid, ciliary body, and iris, while the nervous layer terminates just before the ciliary body. This point is called orra serrata.
• Albinos lack melanin pigment in all parts of the body, including the eye.
• The neural portion of the retina is a multilayered outgrowth of the brain.
• It processes visual data extensively before transmitting nerve impulses to the thalamus, which then relays nerve impulses to the primary visual cortex.
• Three distinct layers of retinal neurons are separated by two zones where synaptic contacts arc made—inner and outer synaptic layers.
• The three layers of retinal neurons, in the order in which they process visual input, are the photoreceptor layer, bipolar cell layer, and ganglion cell layer.
• Note that light passes through the ganglion and bipolar eel! layers before reaching the photoreceptor layer.
• Two other types of cells present in the retina are called horizontal cells and endocrine cells. These cells form laterally directed pathways that modify the signals being transmitted along the pathway from photoreceptors to bipolar cells to ganglion cells.

• Photoreceptors are specialized to transduce light rays into receptor potentials.
• The two types of photoreceptors are rods and cones.
• Each retina has about 6 million cones and 120 million rods.
• Rods are the most important for seeing shades of grey in dim light.
• They also allow us to see shapes and movement.
• Cones provide color vision in bright light.
• The visual pigments for color vision are erythropsin (sensitive to red), chloropsin (sensitive to green), and cyanopsin (sensitive to blue).
• In moonlight, we cannot see colors because only the rods are functioning.
• Due to the low light level cones are not functioning.
• The macula lutea is in the exact center of the posterior portion of the retina, at the visual axis of the eye.
• The central fovea, a small depression in the center of the macula lutea, contains only cone photoreceptors.
• In addition, the layers of bipolar and ganglion cells, which scatter light to some extent do not cover the cones here; these layers are displaced to the periphery of the fovea.
• As a result, the central fovea is the area of highest visual acuity or resolution (sharpness of vision).
• Rods are absent from the fovea and macula and increase in number towards the periphery of the retina.
• From photoreceptors, information flows to bipolar cells through the outer synaptic, layer and then from bipolar cells through the inner synaptic layer to ganglion cells.
• The axons of ganglion cells extend posteriorly to the optic disc and exit the eyeball as optic nerves.
• The optic disc is also called the blind spot since it contains no rods or cones.

Accommodation:

• Accommodation (focusing) is the reflex mechanism by which light rays from objects at various locations in the near visual field are brought to focus on the retina.
• Altering the shape of the lens does this. In bright light, the circular muscle of the iris contracts, the radial muscle relaxes, the pupil becomes smaller, and less light enters the eye, preventing damage to the retina.
• In dim light, the opposite muscular contractions and relaxations occur.
• In the dark of night, your pupil may become up to 16 times bigger.
• The added advantage of reducing the pupil size is that it increases the depth of focus of the eye so that any displacement of the photosensors in the retina will not impair the focus.
• Light rays from distant objects (>6 m) are parallel when they strike the eye.
• Light rays from near objects (<6 m) are diverging when they reach the eye.
• In both cases, the light rays must be refracted or bent to focus on the retina and refraction must be greater for light from near objects.
• The normal eye can accommodate light from objects from about 25 cm to infinity.
• With the involuntary ciliary muscles at rest, the flatter lens has the correct optical properties to focus distant images on the retina, but not close images.
• The state of contraction of the ciliary muscles changes the tension of suspensory ligaments. This acts on the natural elasticity of the lens, which causes it to change its radius of curvature and, thus, the degree of refraction.
• As the radius of curvature of the lens decreases, it becomes thicker, and rounds up, and the amount of refraction increases.
• It is the tension of the suspensory ligaments applied to the lens that determines the shape of the lens.
• When the circular ciliary muscles are relaxed and the suspensory ligament becomes tout, the lens is pulled into a flattened shape suitable for focusing distant objects, decreasing the refraction.
• When the tension is decreased, the circular ciliary muscles are contracted and the suspensory ligaments slack. Consequently, the lens becomes a more spherical shape suitable for focusing objects.
• The image produced by the lens of the eye on the retina is inverted and reversed. However, objects are perceived the right way up because of the way in which the brain interprets the images.
• The region of the environment from which each eye collects light is called the visual field.
• Since both our eyes are frontally placed, there is an overlap between the visual fields of each eye. This is called binocular vision.

Image formation is a refractive process; maximum refraction takes place at the cornea.

Extra-ocular muscle of the eye: The eye is rotated in the orbit by six strap-shaped muscles inserted on the sclera. These are arranged in two groups—rectus and oblique.

Chambers of Eyeball

• The lens and suspensory ligament divide the interior of the eyeball into two chambers, the anterior small aqueous chamber containing a watery fluid, the aqueous humor, and the posterior larger vitreous chamber containing viscous fluid, the vitreous humor.
• Aqueous humor maintains intra-ocular pressure mainly whereas vitreous humor is responsible for the shaping of eyeballs.

Mechanism Of Vision

Protective Devices of Eye:

• Eyebrows: Two arched eminences of skin having numerous hairs project obliquely from the surface of the skin. The function of the eyebrows is to protect the anterior aspect of the eyeball from sweat, dust, and other foreign bodies.
• Eyelids (palpebrae) and eyelashes: The eyelids are two movable folds and have hairs on their free edges—the eyelashes. The third eyelid is vestigial and is called plica semilunaris (nictitating membrane). The inner surface of each eyelid and parts of the eyeball are covered with a mucous membrane, called the conjunctiva.
• Glands of Zeis: These are modified sebaceous glands that are associated with the follicles of eyelashes. They open into the follicles of eyelashes. Meibomian or tarsal glands arc also modified sebaceous glands (oil glands) which are present along the edges of eyelids. They produce an oily secretion that serves to lubricate the corneal surface and hold a thin layer of tears over the cornea.
• Glands of Moll: These are modified sweat glands at the edge of the eyelid.
• Conjunctiva: The palpebral conjunctiva is very vascular and has numerous papillae. Over the sclera the ocular conjunctiva is loosely connected to the eyeball; here it is thin, transparent, without papillae, and slightly vascular. Reaching the cornea, it continues as the corneal epithelium. The epithelium of the palpebral conjunctiva near the margin of the lids is a non-keratin-nized squamous stratified epithelium. The conjunctiva helps to protect the eyeball and keeps it moist. It is this membrane that becomes inflamed in conjunctivitis or “pink eye.”
• Lacrimal apparatus: The lacrimal apparatus of each eye consists of a lacrimal gland and its numerous ducts, the superior and inferior canaliculi, a lacrimal sac, and a nasolacrimal duct. The lacrimal gland secretes tears which are composed of water, salts, and a bactericidal protein called lysozyme. Lysozyme dc- stroys microorganisms present on the front of the eyeball.
• Adipose tissue (fat): A layer of adipose tissue surrounds the eyeball in the orbit. It serves as a soft, shockproof pad.

Disorders of Eye

• Myopia or nearsightedness: In this case, the eyeball is too posteriorly elongated so that the image of distant objects is formed in front of the yellow spot. The defect can be removed by using concave glasses.
• Hypermetropia or longsightedness: The person can see distant objects clearly, but not those which are closer. This is due to the Antero-posterior shortening of the eyeball. Hence, the image forms behind the yellow spot. The defect can be overcome by using a convex lens.
• Presbyopia: A common defect in old age people due to the loss of elasticity of the lens and reduced power of accommodation. The disorder can be corrected by convex lenses.
• Astigmatism: The disorder due to the rough curvature of the cornea or lens which can be corrected by the use of cylindrical glasses.
• Cataract: The sight is impaired due to the lens becoming opaque (said motia). The defect can be cured by surgical removal of the defective lens.
• Glaucoma: It occurs due to an increase in intra-ocular pressure as it may develop due to the blockage of the canal of Schlemm. It exerts pressure on the optic nerve causing its damage. It leads to permanent blindness (kala motia).

Organs of Hearing (Ear)

The organs (phonoreceptors) in man are a pair of ears situated on the head. Apart from their auditory function, the ears are also the organs of balance. Each ear has three portions: external ear, middle ear, and internal ear.

1. External ear

• It consists of a pinna and an external auditory canal. The latter is a curved passage that is lined by a profusion of hair and about 4,000 ceruminous glands.
• The glands secrete cerumen, a waxy material that entraps dust and also lubricates the tympanum.
• The tympanum or eardrum is a circular membrane present on the inner end of the external auditory canal and parts it from the tympanic cavity.

2. Middle ear

• The middle ear is represented by an air-filled tympanic cavity which communicates with the pharynx by a passage called the Eustachian canal.
• Present in the inner wall of the tympanic cavity are two openings, the upper fenestra ovalis and the lower fenestra rotunda, each covered by a membrane.
• The tympanic cavity contains three small bones, the ear ossicles, which from outside to inside include malleus, incus, and stapes.

• The malleus is hammer-shaped; the incus is anvil-shaped, and the stapes are stirrup-shaped.
• The outer arm of the malleus is in contact with the inner surface of the tympanum, while the inner end of the stapes forms contact with the membrane on the fenestra ovalis.
• The middle ear is responsible for the amplification of the signal due to the leverage system of ossicle (10 times) by ear ossicles and 2.2 times by the smaller size of membrane covering fenestra ovalis. The oval window is the door to the internal ear.

3. Internal car

• It is also called a membranous labyrinth and is surrounded by a bony labyrinth of almost similar shape.
• The space between the membranous labyrinth and the bony labyrinth is filled with a watery fluid, perilymph. The membranous labyrinth contains emdo- lymph.
• The internal ear is a delicate organ and is differentiated into vestibule, semicircular canals, and cochlear ducts.
• The vestibule is the central body and is formed of two chambers, the upper utriculus and the lower succulents.
• Semicircular canals are three-arched structures that emerge from the utriculus and open back into it. They include anterior and posterior vertical canals and a horizontal canal.
• The vertical canals join to form a common passage crus commune before they open into utriculus.
• Each semicircular canal is dilated at the base to form an ampulla which contains a sensory spot called a crista formed of receptor cells and supporting cells.
• The receptor cells bear sensory hair, which is embedded into a gelatinous cupitle above.
• The vestibule also contains two sensory spots called maculae, one in the sacculus and another in the utriculus.

• Maculae are similar to cristae, but there is no cupule.
• The sensory hair is embedded in an otolith membrane containing calcareous bodies called otoliths.
• Cristae and maculae are the receptors of balance.
• The auditory region of the internal ear is represented by a spirally coiled structure called the cochlea.
• lt consists of a cochlear duct arising from the sacculus, which is surrounded by a similarly shaped cochlear canal, a part of a bony labyrinth.
• The cochlear duets is fused with the cochlear canal on lateral sides, but is free laterally, therefore, in TS, the cochlea shows three chambers, upper scala vestibuli, middle scala media, and scala tympam.
• The scala media is partitioned from the live scala vestibuli by Reissner’s membrane and from the scala tympani by the basilar membrane.
• Scala vestibule and scala tympam contain perilymph while scala media is filled with endolymph.
• The upper and lower chambers communicate through lielicotrema, a narrow opening present at the distal end of the cochlea.
• The basilar membrane, sensory hair cells, and tectorial membrane make up live smallest unit of the ear, called the organ of Corti, first described by Italian microscopist, Alfonso Corti (1822 1888).

• Sensory hair cells inside the car resemble tracts left in the sand by truck tires.
• The cochlea contains 16,000-24,000 hair cells arranged in four rows.
• In three of the rows, the hairs form V-shaped patterns. In the fourth row, the hairs stand in a straight line.
• Each hair cell has up to 100 hairs.
• When sound vibrations pass through the oval window, hairs create waves in the lymph fluid of the cochlea such as a sea wave in a tidal current.
• The waves cause the basilar membrane to ripple. This movement bends the hair cells, pressing against the tectorial membrane and setting off nerve impulses in their associated afferent neurons.
• More than 30,000 neurons and nerve fibers emerging from these convey electrical signals to the brain.
• just 2 cm away via the auditory (vestibulocochlear) nerve.
• The basal ends of hair cells synapse with the fibers of a cochlear branch.
• When the waves reach the round windows of the cochlea, they die away.

Mechanism Of Hearing

• The high-frequency resonance of the basilar membrane occurs near the base, where the sound waves enter the cochlea, while low-frequency resonance occurs near the apex mainly because of the stillness of the fibers of the basilar membrane.
• The three internal ossicles of car are malleus, incus, and stapes.
• In the case of non-mammals (amphibians, reptiles, birds), there is just one bone called columella auris.

Physiology Of Equilibrium

There are two kinds of equilibrium (balance):

1. One is called static equilibrium, which refers to the maintenance of the body position (mainly the head) relative to the force of gravity.
2. The second is dynamic equilibrium, which is the maintenance of body position (mainly the head) in response to sudden movements such as rotation, acceleration, and deceleration.

Collectively, the receptor organs for the equilibrium arc are called vestibular apparatus, which includes saccule, utricle, and semicircular ducts.

1. Static Equilibrium

• The walls of both utricle and saccule contain a small, thickened region called macula (plural maculae)
• Maculae are the receptors for static equilibrium and also contribute to some aspects of dynamic equilibrium.

• Static equilibrium provides sensory information on the position of the head and is essential for maintaining appropriate posture and balance.
• For dynamic equilibrium, they provide information about linear acceleration and deceleration. For example, the sensation you feel while in an elevator or a car that is speeding up or slowing down.

2. Dynamic equilibrium

• The vestibular apparatus contains three semicircular canals positioned at right angles to one another.
• The dilated portion of each duct, the ampulla, contains a small elevation called a crista.
• Each crista is composed of a group of hair cells, supporting cells covered by a mass of gelatinous material called cupula.
• Cristae in the three semicircular canals maintain dynamic equilibrium.

Diseases of the Ear

• Meniere’s disease: Due to increased amount of the fluid of internal ear, loss of hearing.
• Myringitis: inflammation of the tympanic membrane.
• Otitis media: Acute infection in the middle car.
• Vertigo: A type of dizziness where there is a feeling of motion when one is stationary.
• Cobyrinthine diseases: Improper functioning of the internal car.

1. Most domestic mammals and sharks lack color vision.
2. Tapetum lucidum: It is a part of the choroid adjacent to the retina in the eyes of a large number of elasmobranchs (cartilaginous fish). It possesses cells containing light-reflecting guanine crystals. It reflects light and causes the eyes to shine in the dark. It also reflects additional light on the retinal cells to enable the fish to see in water where light is poor.
3. Accommodation: Fishes can see objects at different distances by changing the size of the eyeball.
4. Pecten: It is a remarkable, highly vascular, and pigmented structure projecting into the vitreous chamber from the blind spot normally. It occurs in all birds except Kiwi (Apteryx). It is also found in some reptiles (e.g. Uromastix) but is absent in mammals. In Uromastix, it is like a cushion; however, in a pigeon, it is comb-like and folded like a fan. The actual function of pecten is unknown, but possibly it aids in the nutrition of the eyeball. In birds, it also helps in accommodation which is remarkably well developed in birds, by pressing the lens forward.
5. Phaco-emulsification technique in cataract surgery is a “stitchless” technique. A foldable intraocular lens (IOL) is used.
6. Most birds have only day vision as their retina has mainly cones.
7. Owls have much better night vision as they contain a large number of rods and few cones in their retina.
8. The taste of chilies is not a true sensation. It is mainly the sensation of burning pain produced by the stimulation of pain receptors of the tongue.
9. Hordeolum: Inflammation of sebaceous glands of the eyelid.
10. Owls and cats see only with the help of available light from the stars or moon at night.
11. Frogs are short-sighted in air and long-sighted in water.
12. Many insects such as honeybees possess gustatory receptors on their feet.
13. Largest cranial nerve —trigeminal.
14. Smallest/thinnest cranial nerve —pathetic/trochlear.
15. Other names of various parts of the brain:
    • Forebrain = Prosencephalon
    • Midbrain = Mesencephalon
    • Hindbrain* Rhombencephalon
    • Olfactory lobes = Rhinencephalon
    • Cerebrum = Telencephalon
    • Diencephalon = Thalamencephalon
    • Cerebellum and Pons = Metencephalon
    • Medulla oblongata = Myelcncephalon
    • Fourth ventricle = Metacoel
    • Third ventricle = Diocoel
    • Iter = Mesocoel and aqueduct ofsylvius.
    • Lateral ventricle = Paracoel
    • Spinal canal = Myelocoel
    • The cavity of the olfactory lobe = Rhinocoel (absent in humans)
16. The origin of CNS develops from a neural tube that is formed by the infolding of the ectoderm in the early embryo.
17. Neopallium: The dorsal wall of the cerebrum/cerebral cortex of the brain.
18. Monosynaptic/simple reflex involves a single sensory fiber and a single motor fiber, for example, knee jerk. No interneuron. Polysynaptic/compound reflex involves one (or more) sensory and more than one motor nerve fiber. A number of interneurons are present. Polysynaptic reflexes are more common. All our visceral reflexes are polysynaptic.

 

Neural Control And Coordination Assertion-Reasoning Questions

In the following questions, an Assertion (A) is followed by a corresponding Reason (R). Mark the correct answer.

1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
3. If Assertion is true, but Reason is false.
4. If both Assertion and Reason are false.

Question 1.

Assertion: In the nervous system, the generation of an action potential depends upon the influx of sodium ions into the axoplasm.

Reason: The influx of sodium ions during nerve impulse generation is due to the efflux of potassium ions.

Answer: 3. If Assertion is true, but Reason is false.

Question 2.

Assertion: The presence of myelin sheath increases the rate of conduction of nerve impulses.

Reason: Ionic channels are absent in the area covered by the myelin sheath. Therefore, depolarization occurs only at the nodes of Ranvier, resulting in saltatory or jumping conduction.

Answer: 3. If Assertion is true, but Reason is false.

Question 3.

Assertion: Receptors in the tendon, and joints give information regarding the position and movements of different parts of the body.

Reason: These are termed as noci-receptors.

Answer: 3. If Assertion is true, but Reason is false.

Question 4.

Assertion: The sharpest vision is in fovea centralis.

Reason: The relationship of receptor to bipolar cells to ganglion cells is 1: 1: 1 within fovea centralis.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 5.

Assertion: The postganglionic nerve fiber of the parasympathetic nervous system has acetylcholine while the sympathetic nervous system has adrenaline as the neurotransmitter.

Reason: The sympathetic nervous system inhibits intestinal peristalsis while the parasympathetic stimulates peristalsis.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 6.

Assertion: The brain and spinal cord have a common covering.

Reason: Both the brain and spinal cord possess meninges.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 7.

Assertion: Cerebrospinal fluid is present throughout the central nervous system.

Reason: CSF has no such function.

Answer: 3. If Assertion is true, but Reason is false.

Question 8.

Assertion: The brain stem contains centers for controlling activities.

Reason: The brain stem is very sensitive.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 9.

Assertion: The spinal cord has a column of both grey and white matter.

Reason: Grey matter forms the central spinal canal.

Answer: 3. If Assertion is true, but Reason is false.

Question 10.

Assertion: The motor end plate is a neuromuscular junction.

Reason: The motor end plate is the junction between motor neurons and muscle fibers.

Answer: 1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

Question 11.

Assertion: Corpus callosum is present in the space between the pia and arachnoid maters.

Reason: It serves to maintain a constant pressure inside the cranium.

Answer: 4. If both Assertion and Reason are false.

Question 12.

Assertion: With the evolution of multicellularity, it became imperative to develop a nervous system.

Reason: Special senses such as vision, and hearing are produced by sense organs associated with the nervous system.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Question 13.

Assertion: The auditory ossicles help in hearing.

Reason: Auditory ossicles maintain the balance of air pressure between two sides of the eardrum.

Answer: 3. If Assertion is true, but Reason is false.

Question 14.

Assertion: The image focused on the fovea is seen most accurately.

Reason: The Fovea of the retina contains numerous photoreceptor rod cells.

Answer: 3. If Assertion is true, but Reason is false.

Question 15.

Assertion: A blind spot on the retina of the eye is devoid of the ability for vision.

Reason: The photoreceptor cone cells are absent at the blind spot.

Answer: 2. If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.