NEET Biology

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.

” microbes in human welfare”

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.

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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.

” microbes in household products class 12″

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:

“chapter 10 biology class 12 notes “

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.

ch 10 biology class 12 notes

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).

NEET Biology Notes For 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.

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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.

” class 12 biology ch 9 notes”

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.

NEET Biology Notes For Strategies For Enhancement In Food Production 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.

class 12 biology chapter 9 notes

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.

NEET Biology Notes For Strategies For Enhancement In Food Production 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.

NEET Biology Notes For Strategies For Enhancement In Food Production 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.

NEET Biology Notes For Strategies For Enhancement In Food Production 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.).

NEET Biology Notes For Strategies For Enhancement In Food Production 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.

NEET Biology Notes For Strategies For Enhancement In Food Production 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.

NEET Biology Notes For Strategies For Enhancement In Food Production Assertion-Reasoning Questions

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

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

Question 1. Assertion: Bulls not selected for breeding are castrated when young and converted to bullocks.

Reason: They are the main source of animal drought power in India.

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

Question 2. Assertion: Anthrax is caused by a bacterium.

Reason: Anthrax develops only in buffaloes and cannot be transferred to humans.

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

Question 3. Assertion: In anthrax, the animal dies due to lack of oxygen.

Reason: The anthrax bacterium uses up the oxygen carried by the animal blood.

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

Question 4. Assertion: Cattle breeds can be improved by super ovulation and embryo transplantation.

Reason: Super ovulation in high milk yielding cows is induced by hormonal injection.

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

Question 5. Assertion: Honey is an animal product produced by honey bee.

Reason: Honey contains only sugar, nothing else.

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

Question 6. Assertion: India ranks fifth in the world in catile population but figures poorly in milk production.

Reason: Buffaloes give more milk with higher fat and mineral contents than cows.

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

Question 7. Assertion: Poultry farming has definite advantage over livestock rearing.

Reason: Poultry birds are easy to raise, can be acclimatized to a wide range of climatic conditions, have short lifespan, and are prolific breeders.

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

Question 8. Assertion: Encephalomalacia, a disease of poultry, is caused by the protozoan Eimeria.

Reason: Encephalomalacia causes bloody diarrhea in poultry.

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

Question 9. Assertion: Fish meal is a rich source of protein for cattle and poultry.

Reason: Fish meal is prepared from the non-edible parts of fishes such as tails, fins, and bones.

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

Question 10. Assertion: Somatic hybrids may be used for the production of useful plants.

Reason: Genetic manipulation can be carried out more rapidly when plant cells are in protoplast state.

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

Question 11. Assertion: Callus is obtained within 2-3 weeks.

Reason: Suspension culture grows much faster than callus culture.

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

Question 12. Assertion: Genetic improvement of the crop is plant breeding.

Reason: It creates desired plant types that are better suited for cultivation.

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

Question 13. Assertion: The phase between 1960-1970 is often called the Green Revolution.

Reason: The development of several high yielding varieties of wheat and rice in 1960’s increased yields per unit area.

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

Question 14. Assertion: The maize having high nitrogen, sugar, and aspartic acid is resistant to pest.

Reason: It develops resistance to maize root borers.

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

NEET Biology Notes  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.

” respiration in plants class 11 handwritten notes”

• 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

NEET Biology Notes  Respiration In Plants 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.

NEET Biology Notes  Respiration In Plants 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.

“respiration notes “

• 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:

NEET Biology Notes  Respiration In Plants 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

NEET Biology Notes  Respiration In Plants 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).

“respiration in plants diagram “

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.

” ch 14 bio class 11 notes”

Electron Transport System: Reactants And Products:

NEET Biology Notes  Respiration In Plants 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.

NEET Biology Notes  Respiration In Plants 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

NEET Biology Notes  Respiration In Plants 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.

NEET Biology Notes  Respiration In Plants 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.

” respiratory balance sheet class 11″

NEET Biology Notes  Respiration In Plants 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.

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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.

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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.

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class 11 neural control and coordination

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.

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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.

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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.

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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.