Category: Class 12 Biology

NCERT Solutions For Class 12 Biology Strategies for Enhancement in Food Production

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 9 Strategies for Enhancement in Food Production:

Section Name	Topic Name
9	Strategies for Enhancement in Food Production
9.1	Animal Husbandry
9.2	Plant Breeding
9.3	Single Cell Proteins
9.4	Tissue Culture
9.5	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Explain in brief the role of animal husbandry in human welfare.
Ans: Animal husbandry deals with the caring, feeding and management of domesticated animals. It includes poultry, farming and fisheries.
These animals are very useful for human beings because
(i) they provide products which are used as food like meat, milk, eggs, honey, etc.
(ii) there are some other substances obtained from animals which are beneficial to human beings like wool, silk, leather, bees wax etc.

2. If your family owned a dairy farm, what measures would you undertake to improve the quality and quantity of milk production?
Ans: To improve the quality & quantity of milk production, one should take care of the following points:
(i) Proper feeding of the cattle with good quality of food.
(ii) Clean and hygienic environment for cattles.
(iii) Proper medication.
(iv) Veterinary supervision.
(v) Selection of good breeds having high yielding capacity combined with resistance to disease.
(vi) Quality of breed.

3. What is meant by the term ‘breed’ ? What are the objectives of animal breeding?
Ans: A group of animals related by descent and similar in most characters like general appearance, features, size, configuration etc. is called a breed.
The main objectives of animal breeding are:

• To produce high yielding varieties of animals like high milk producing cattle, more egg producing varieties of chicken, more wool bearing sheep varieties etc.
• To produce drought varieties for doing work like cattle, etc.
• To produce disease resistant varieties of the livestocks.

4. Name the methods employed in animal breeding. According to you which of the methods is best? Why?
Ans: Methods employed in animal breeding are
(i) Inbreeding
(ii) Out-breeding
(iii) Cross-breeding
(iv) Interspecific hybridization
(v) Artificial insemination
(vi) Multiple Ovulation Embryo Transfer Cross breeding is the best method as it results in the development of superior traits of both the breeds and the progeny produced are fertile and there is no inbreeding depression.

5. What is apiculture? How is it important in our lives?
Ans: Apiculture is the rearing and breeding of honeybees for the production of honey .
It is important in our live as honeybees provide honey, which is a highly nutritive substance and beeswax is used in many industries. Honeybees also pollinate flowers of some very important plants like sunflower, apple, pear.

6. Discuss the role of fishery in enhancement of food production.
Ans: Fishery is an industry which is concerned with the catching, processing or selling of fish. The role of fishery in enhancement of food production is as follows :

1. The fish flesh is an excellent source of protein. It has very little fat, carries a good amount of minerals and vitamins A and D and is rich in iodine.
2. Fish oil extracted from the liver of the sharks, sawfishes, etc., has medicinal value.
3. Shagreen, the skin of sharks and rays are used in polishing the wood and other materials.
4. The silvery bony scales of cyprimids are used in the manufacture of artificial pearls.
5. Fish glue is a sticky product obtained from the skin of cod and is used as gum.
6. Fish waste after the extraction of oil is used as fertilizer.
7. The fishing industry has brought a lot of income to the farmers in particular and the country in general because of “Blue Revolution” (fish production) in the same lines as ‘Green Revolution’ (for producing enough food for all).

7. Briefly describe various steps involved in plant breeding.
Ans: Plant breeding is a purposeful manipulation of plant species in order to create desired plant types that are better suited for cultivation, give better yields and are disease resistant. The given flow chart shows various steps involved in plant breeding.

8. Explain what is meant by biofortification.
Ans: Enhancement of nutritional quality of a crop by improving the content and quality of protein, fats, vitamins, minerals and micronutrient is called biofortification. It helps to improve public health.

9. Which part of the plant is best suited for making virus-free plants and why?
Ans: The apical and axillary meristems of plants are the best parts of the plant to make virus-free plants. This is because rate of division of meristematic cell is higher than rate of multiplication of virus and viruses are unable to invade newly formed meristematic cells. Hence, meristematic cells are free of virus although the whole plant is infected with virus. With the use of meristem, a healthy plant can be recovered from the diseased plant through micropropagation method.

10. What is the major advantage of producing plants by micro propagation?
Ans: It is faster method of producing a large number of plants. Plants formed by micro propagation are identical.

11. Find out the various components of the medium 12.used for propagation of an explant in vitro are ?
Ans: The various components of the medium used for propagation of an explant in vitro are
-Sucrose (source of energy & carbon)
-Inorganic salts
-Vitamins
-Growth regulators (auxins and cytokinins)

12. Name any five hybrid varieties of crop plants which have been developed in India.
Ans: Sonalika (wheat)
Himgiri (wheat)
Pusa Swamim (mustard)
PusaSem2 (bean)
Pusa Sawani (lady’s finger)

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NCERT Solutions For Class 12 Biology Human Health and Disease

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 8 Human Health and Disease:

Section Name	Topic Name
8	Human Health and Disease
8.1	Common Diseases in Humans
8.2	Immunity
8.3	AIDS
8.4	Cancer
8.5	Drugs and Alcohol Abuse
8.6	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1.What are the various public health measures, which you would suggest as safeguard against infectious diseases?
Ans. The various public health measures against infectious diseases includes the following –
1.Education – People should be educated about the infectious diseases so that they may protect themselves against the infections.
2.A people suffering from any infections should be isolated to avoid its transmission to any other person.
3.Vaccination – People should get vaccination to avoid infection. Vaccination is available against cholera, typhoid, TB etc.
4.Sanitation – Sanitary surroundings can prevent spread of diseases. Public hygiene includes – suitable disposal of waste & human excreta; periodic cleaning and disinfection of water sources; observing normal practices of hygiene in public catering. Personal hygiene includes keeping the body clean, intake of clean drinking water, vegetables, fruits etc.
5.Eradication of vectors – The breeding places of vectors should be destroyed & adult vectors killed by appropriate methods.

2.In which way has the study of biology helped us to control infectious diseases?
Ans.The science that makes a study of diseases is called pathology, though in a broad sense it includes diagnostic, prophylactic and curative measures too. Pathology is a study of diseases of all kinds though we will confine ourselves to the diseases caused by a pathogenic organism, the reaction of the host as shown in the form of symptoms, the diagnosis made through a study of their symptoms, etiology of the pathogenic organism and finally steps undertaken to cure the host of its diseases, by eradicating and if it is not possible, by controlling the pathogen. In this way the study of biology helped us to control infectious diseases.

3. Hovy does the transmission of each of the following diseases take place?
(a)Amoebiasis (b) Malaria
(c)Ascariasis (d) Pneumonia
Ans. (a) Amoebiasis – It is usually contracted by ingesting water or food contaminated by amoebic cysts.
(b)Malaria – It is transmitted from one person to another by the female Anopheles mosquito. The mosquito picks up the parasite along with the blood when it bites an infected person. When this mosquito bites an other healthy person, the parasites migrate into his blood with the saliva, which the mosquito injects before sucking up blood to prevent its clotting.
(c)Ascariasis – Transmitted through water, vegetables, fruits etc. contaminated with the eggs of the parasites.
(d)Pneumonia – Spreads by cough & sneezes, by sharing drinking glass & eating utensils with an infected person.

4.What measures would you take to prevent water borne diseases?
Ans: Water borne diseases can be prevented by –
(i) Oral dehydration
(ii) Health education
(iii) Control of reservoirs
(iv) Immunization
(v) General hygiene, pure water

5. Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.
Ans: A DNA vaccine consists of a suitable gene encoding an antigenic protein, inserted into a plasmid, and then incorporated into the cells in a target animal. The plasmid vaccine carrying the DNA (gene) enters the nucleus of target cells and produces RNA, and in turn the specific antigenic protein, because these proteins are recognized as foreign. When they are processed by the host cells and displayed on their surface, the immune system is alerted, which then triggers a range of immune responses.

6. Name the primary and secondary lymphoid organs.
Ans: Primary lymphoid organs – Bone marrow and thymils.
Secondary lymhoid organs – Spleen, lymph nodes, tonsils.

7. The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its fall form:
(a) MALT
(b) CMI
(c) AIDS
(d)NACO
(e) HIV
Ans: (a) MALT – Mucosal Associated Lymphoid Tissue
(b) CMI-Cell-Mediated Immunity
(c) AIDS – Acquired Immuno Deficiency syndrome
(d) NACO – National AIDS Control Organization
(e) HIV – Human Immuno Deficiency Virus

8. Differentiate the following and give examples of each
(a) Innate and acquired immunity
(b) Active and passive immunity
Ans: (a) Innate & acquired immunity
Innate immunity, also called inherent, natural, non specific immunity, comprises all those defence elements with which an individual is bom & which are always available to protect a living body. It acts on many organisms and does not show specificity, e.g. Lysozyme present in secretions such as tears, catalyzes the hydrolysis of molecules in the cell walls of bacteria & interferon induces antiviral state in non infected cells. They act as physiological barriers & check the growth of many pathogenic micro-organisms. Acquired immunity, also called adaptive or specific immunity, is the immunity obtained either from the development of antibodies in .response to exposure to an antigen, as from vaccination or an attack of an infectious diseases or from the transmission of antibodies as from mother to foetus through the placenta.

(b) Active & passive immunity
Active immunity is acquired by catching & surviving an infectious disease or by vaccination with a weakened form of the diseases which makes the body to form antibodies. Whereas passive immunity is conferred by transfer of immune products like antibodies etc. from other individual

9. Draw a well-labelled diagram of an antibody
Ans:

10. What are the various routes by which trans-mission of human immunodeficiency virus takes place?
Ans: Various routes by which transmission of human immunodeficiency virus takes place are
(i) Illicit sexual contact.
(ii) Sexual contact with multiple partners.
(iii) Transfusion of the blood of infected person.
(iv) Intravenous drug users that shares needles are at high risk of contracting AIDS.

11. What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
Ans: HIV critically injures the immune system by infecting and eventually killing T-cells. Once the virus has infected a T cell, HIV copies its RNA into double stranded DNA copy by mearis of viral enzyme reverse transcriptase. This process is called reverse transcriptase because it violates the usual way in which genetic information is transcribed. Because reverse transcriptase lacks thg proofreading function that most DNA synthesizing enzymes have, many mutations arises as the virus replicates, further hindering the ability of the immune system to combat the virus. These mutations allow the virus to evolve rapidly resulting in the lost of vital cells. As a result of progressive destruction of its T-cells, the body is easily ravaged by a number of common infectious agents. In many instances, these infections would have caused little injury if there functional T-cells clones available.
Death ultimately results from the relentless attack of opportunistic pathogens or from the body’s inability to fight off malignancies.
virus. These mutations allow the virus to evolve rapidly resulting in the lost of vital cells. As a result of progressive destruction of its T-cells, the body is easily ravaged by a number of common infectious agents. In many instances, these infections would have caused little injury if there functional T-cells clones available.
Death ultimately results from the relentless attack of opportunistic pathogens or from the body’s inability to fight off malignancies.

12. How is a cancerous cell different from a normal cell?
Ans: Cancer is a disease characterized by the excessive and abnormal growth of certain cells. In a healthy individual, the growth of cells is balanced by the rate of cell loss. Thus, when one attains adult age, the size and cellular contents of various body organs remain constant. The balance between the growth of the cells and the rate of cell class may be dislocated by certain chemicals, physical stresses and viral agents. As a result, the normal growth of the cells may be transformed into cancerous one. Cancerous cells acquire the ability to invade new sites, a phenomenon called metastasis. They exhibit a number of alterations on cell surface, in the cytoplasm, and in their genes. These features are used for the identification of cancers.

13. Explain what is meant by metastasis.
Ans: Metastasis is the phenomenon in which cancer cells due to unregulated proliferation spread to distant sites through body fluids to develop secondary tumors. Only malignant tumors show the property of metastasis.

14. List the harmful effects caused by alcohol/drug abuse.
Ans: Harmful effects caused by alcohol abuse are –
(i) Alcohol generates more energy mostly in the form of heat, but at the same time, it dilates the blood vessels. Consequently the ‘heat generated is rapidly lost. Due to constant dilation, the arterial walls soon become brittle & rigid. Such a change in the property of blood vessels & deposition of alcoholic fat affect the working of heart.
(ii) Alcoholism leads to gastric ulcers & gastritis.
(iii) In chronic alcoholism, the axon of the nerve inflame thus causing neuritis.
(iv) Permanent damage to liver cells occur due to deposition of fats. The liver dries up & harden (cirrhosis).
Harmful effects caused by drug abuse are –
(i) Excessive doses of drugs may lead to coma & death due to respiratory failure, heart failure & cerebral haemorrhage.
(ii) Lack of interest in personal hygiene, withdrawal, isolation, depression, fatigue aggressive & rebellious behaviour etc.
(iii) Acquire serious infections like AIDS & hepatitis B, who take drugs intravenously.
(iv) The adverse effects of drugs are manifested in the form of reckless behaviour, vandalism & violence.

15. Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
Ans: Yes, friends can influence one to take drugs. Following measures can be taken:
(i) Avoiding undue peer pressure.
(ii) Not taking undue pressure of failures beyond its threshold.
(iii) Getting counselling from some counsellor
(iv) Seeking help from parents and peers
(v) Seeking medical help

16. Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.
Ans: Psychological & physiological dependence of an individual to the intake of certain kinds of drugs and alcohol is called addiction. Once a person start taking alcohol & drugs, it is very difficult to get rid this habit because addiction drive people to take them even when these are not needed or even when their use becomes self destructive. With repeated use of drugs, the tolerance level of the receptors present in the body increases, consequently, the receptors responds only to higher doses of drugs or alcohgl leading to greater intake & addiction. Thus, the addiction potential of drugs & alcohol, pull the user into a vicious circle leading to their regular use (abuse) from which he/she may not able to get out.

18. In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
Ans: Human have probably been using mind – affecting drugs since time immemorial. The root cause of addiction of man to drugs, smoking and drinking has been due to his inability to make mental adjustments with stresses and strains, drudgery and extreme misery in daily life. As a temporary measure, to combat these adverse situations and to have a certain degree of mental relaxation, humans have been making an extensive use of stimulants, depressants and hallucinogens. Stimulants generally speed up body process, and depressants slow them. Hallucinogens can alter a person’s thoughts, feelings, and perception.
In preventing drug abuse, the role of parents
could be:
(i) Communicate openly with the children, listen to their problems patiently and teach them how to handle the problems.
(ii) Take interest in children’s activities and their friends circle.
(iii) Set an example for children by not taking drugs or alcohol.
(iv) Keep track of prescribed drugs in home.
(v) Learn as much as possible about drugs.

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NCERT Solutions For Class 12 Biology Environmental Issues

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 16 Environmental Issues:

Section Name	Topic Name
16	Environmental Issues
16.1	Air Pollution and Its Control
16.2	Water Pollution and Its Control
16.3	Solid Wastes
16.4	Agro-chemicals and their Effects
16.5	Radioactive Wastes
16.6	Greenhouse Effect and Global Warming
16.7	Ozone Depletion in the Stratosphere
16.8	Degradation by Improper Resource Utilisation and Maintenance
16.9	Deforestation
16.10	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Ans:  Domestic sewage contains four kind of impurities:
(i) Suspended solids: They are soil particles such as sand and silt.
(ii) Colloidal particles: They are inorganic and organic materials such as faecal matter, bacteria, paper and cloth.
(iii) Dissolved solids : They are nitrates, phosphates, ammonia, sodium, calcium and other nutrients.
(iv) Pathogens : Domestic sewage has pathogens of various diseases such as typhoid, cholera, dysentery, diarrhoea, etc. Effect of sewage discharge on river are:
(i) Eutrophication.
(ii) Growth of pathogenic bacteria.
(iii) Ageing of river where slit and decaying matters start accumulating and filling river.
(iv) Increase in BOD.
(v) Destruction of flora and fauna of that river.

2. List all the wastes that you generate at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?
Ans: Waste materials generated at home : paper, disposable cups, cloth, plates, spoons, plastic envelopes, discarded food etc.

Waste materials generated at school are : paper, chalks, plastic envelopes etc.

Wastes materials generated during trips are : paper, disposable cups, plates, spoons, plastic envelopes, discarded food etc.

No, we cannot reduce the generation of these wastes easily, but few can be reduced. The wastes belong to two categories : biodegradable and non-biodegradable. It is difficult or rather impossible to reduce discarded food like peel of potato, peel of banana etc. We can do one important thing i.e., to reduce wastage of food.

3. Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
Ans: Increase in atmospheric concentration of green house gases has resulted in rise of atmospheric temperature by 0.6°C (global wanning) in die 20th century. This has been confirmed by intergovernmental panel on climatic change (IPCC) in its reports of 1991 and 1992. This predictable change in near future may affect climate, sea level, range of species distribution, food production as well as fisheries resources in the oceans.
Causes of global warming:
(i) Increase in concentration of greenhouse gases.
(ii) Increase of automobile and use of fossil fuel.
(iii) Deforestation and change in land use.
(iv) CFC and aerosol emission from refrigerator and aeroplane.
(v) Increased particulate matter in lower atmosphere.
Effects of global warming:
(i) CO₂ fertilisation effect.
(ii )Many species of plants, being sensitive to temperature will die with sudden rise in temperature and their place will be taken over by scrub vegetation.
(iii) Loss of biodiversity.
(iv) Rise in sea level.
(v) Possibilities of drought and floods.
(vi) Erruption of plant disease and pests.
(vii) Change in rainfall pattern.
Methods that can reduce the atmospheric concentration of greenhouses gases are
(i) Reducing the greenhouse gas emission by limiting the use of fossil fuels, and by developing alternative renewable sources of energy (wind energy, solar energy etc.)
(ii) Increasing the vegetation cover, mainly the forests, for photosynthetic utilization of CO₂.
(iii) Minimizing the use of nitrogen fertilizers in agriculture for reducing N₂O emissions.
(iv) Developing substitutes for chlorofluorocarbons.

4. Match the items given in column A and B:

Ans: (a)-(iii),(b)-(iv),(c)-(i),(d)-(ii)

5. Write critical notes on the following:
(a) Eutrophication
(b) Biological magnification
(c) Groundwater depletion and ways for its replenishment
Ans: (a) Eutrophication : It is excessive growth of algae, plants and animals in water bodies due to the nutrient enrichment particularly with nitrogen and phosphorus. It is both natural and accelerated. It leads to loss of bio-diversity and cuases chemical accumulation in food chain and ageing of water body.

(b) Biological magnification : Increase in concentration of persistent chemical at successive trophic levels is called eutrophication. This happens because a toxic substance accumulated by an organism can not be metabolized or excreted, and is thus passed onto next trophic level, e.g., DDT.

(c) Ground water depletion and replacement: Ground water depletion, a term often defined as long term water level declines caused by sustained ground water pumping, is a key issue associated with ground water use. Many areas of India experiencing ground water depletion.
The most servere consequence of excessive ground water pumping is that the water table, below which the ground is saturated – with water, can be lowered. If ground water level declines too far, then the well owner might have to deepen the well, drill a new well, or at least attempt to lower the pump.

6. Why ozone hole forms over Antarctica? How will enhanced ultraviolet radiation affect us?
Ans: Chlorofluorocarbons, mainly released in the atmosphere by developed countries, Slowly enters the stratosphere and the winds move them towards the poles. Environmental conditions prevailing in Antarctica during winter months; there is no sunlight in Antarctica and extremely low temperature ( – 85°C) facilitates the formation of ice clouds. During winter, natural circulation of wind (polar vertex) completely isolates Antarctic air from the rest of the world.

The ice clouds provide the catalytic surface for the reaction of chlorine atoms and then ozone. But this degradation of ozone occurs with the return of solar radiations to Antarctica during spring (September and October). This results in the thinning of ozone layer every year over most of Antarctica. This hole disappears in summer due to warming up of air and the mixing up of Antarctic air with that of the rest of the world.
Enhanced UV radiations on earth would affect humans and other animals by causing:

• Skin cancer
• Blindness and increased chances of cataract in eyes.
• Malfunctioning of immune system.
• Higher number of mutations.

7. Discuss the role of women and communities in protection and conservation of forests.
Ans: Amrita Bishnoi Wildlife protection project The Bishnoi community is known for its peaceful coexistence with nature. It was in 1730 AD. Amrita Devi protested against king’s men’s attemptto cut trees as it was prohibited in Bishnoi religion. It was a party of Maharaja Abhay Singhji, Rular of Marwar (Jodhpur) state who wanted to fell green khejdali trees. Amrita Devi fy her three daughter & more than 360 of other Bishnois lost their lives in saving trees & became martyers. Later ‘Chipko’ movement’ was started by Sunderlal Bahuguna and others to prevent cutting of trees. The people showed enormous bravery in protecting trees from the axe of contractors by hugging them.

8. What measures, as an individual, would you take to reduce environmental pollution?
Ans: To reduce environmental pollution we should take following measures:
(i) Reducing use of CFC.
(ii) Disposing off waste safely.
(iii) Reducing use of polythene.
(iv) Not disposing off waste in water bodies.
(v) Making automobiles pollution free.
(iv) Prevention of noise pollution by using fire crackers/TV/musical instruments at permissible limits.
(vii) Tree plantation in school, around residence.

9. Discuss briefly the following:
(a) Radioactive wastes
(b) Defunct ships and e-wastes
(c) Municipal solid wastes
Ans: (a) Radioactive waste : Radioactive waste include materials that are radioactive & for which there is no further practical use. These are generated by nuclear reactor, nuclear fallout, man made (refining and mining of platinum and thorium), natural radioactive waste and release of radiation in radiation therapy.
Increased risk of cancer, birth defects & infertility are few harmful effects caused by nuclear waste. So, nuclear waste is an extremely potent pollutant.

(b) Defunct ships & e-wastes – The dismantling of defunct ship is a technically complex process, which is potentially harmful to the environment & human health. Defunct i ships contain toxicants like asbestos, mercury, etc. The workers breaking the ships are not suitably protected and are exposed to toxic chemicals. The coastal areas in the vicinity of the ship-breaking yard also becomes polluted. At the international level, it is accepted that there is uncertainty about the relevant controls for the dismantling of such vessels & there is an urgent need to establish a specific enforceable control framework.
Electronic waste comprised of irrepairable computer and other electronic goods, generated by developed countries.
It is valuable source of secondary raw materials, if treated properly, however if not treated properly it is the major source of toxins. Eventually recycling is the only solution for the treatment of e-wastes provided it is carried out in an environment friendly manner.

(c) Municipal solid wastes : These are commonly known as trash or garbage. It consists of everyday items such as product packaging, furniture, clothing, bottles, food scraps, newspapers.
appliances, paints, batteries etc. Source reduction, recycling and compositing are several municipal social waste management practices. Source reduction involves altering the design, manufacture or use of products & materials to reduce die amount and toxicity of what gets thrown away. Recycling diverts items such as paper, glass, plastic & metals into anew products. Composting decomposes organic waste such as food scraps & yard trimmings with micro-organisms, producing a humus-like substance.

10. What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
Ans: The initiatives were taken for reducing vehicular air pollution in Delhi are :-
(i) Introduction of CNG
(ii) Enforcement of pollution control law
(iii) Introduction of green zones
(iv) Use of unleaded fuels
(v) Replacement of old vehicle with new one. The result is that the air quality of Delhi has improved considerably with a substantial fall in pollutant gases.
(vi)Use of catalytic converters in vehicles.
(vii)Application of Euro II norms for vehicle.

11. Discuss briefly the following:
(a) Greenhouse gases
(b) Catalytic converter
(c) Ultraviolet B
Ans: (a) Greenhouse gases: Gases that trap the heat of the sun in the earth’s atmosphere increasing atmospheric temperature effect are called greenhouses gases. CO₂, CH₄, N₂O and CFC, cause greenhouse. In the absence of greenhouse gases, the temperature of earth would go down to -18°C. The net effect of higher GHGs will be disastrous, (i) Melting of polar ice caps and mountain snow caps resulting in rising of sea level threatening submergence of many islands and coastal areas. Odd climate changes like El Nino. Increased floods and drought.
(b) Catalytic converter : Catalytic converter ‘are used to reduce emission of poisonous gases like nitrogen oxides, carbon monoxide & un reacted hydrocarbon in automotive emission. It is made of platinum, palladium and rhodium and is used as catalyst. It converts unbumt hydrocarbons into CO₂. The only precaution required is not to use gasoline having lead as lead inactivates the catalysts of the converter.
(c) Ultraviolet B : Ultraviolet B is one of the three types of invisible light rays given off by the sun. Ultraviolet B penetrates the ozone layer in attenuated form & reaches earths. This is more over equator than poles due to thinning of ozone shield over equator. It causes skin cancer, reduce rate of photosynthesis in phytoplanktons, reduces diversity of aquatic ecosystem.

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NCERT Solutions For Class 12 Biology Ecosystem

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 14 Ecosystem:

Section Name	Topic Name
14	Ecosystem
14.1	Ecosystem–Structure and Function
14.2	Productivity
14.3	Decomposition
14.4	Energy Flow
14.5	Ecological Pyramids
14.6	Ecological Succession
14.7	Nutrient Cycling
14.8	Ecosystem Services
14.9	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Fill in the blanks.
(a) Plants are called as————- because they fix carbon dioxide.
(b) In an ecosystem dominated by trees, the pyramid (of numbers) is————- type.
(c) In aquatic ecosystems, the limiting factor for the productivity is————- .
(d) Common detritivores in our ecosystem are————- .
(e) The major reservoir of carbon on earth is————- .
Ans: (a) Autotrophs
(b) Spindle
(c) Sunlight
(d) Earthworm, bacteria & fungi of decay and vulture
(e) Oceans

2. Which one of the following has the largest population in a food chain?
(a) Producers
(b) Primary consumers
(c) Secondary consumers.
(d) Decomposers
Ans: (d)

3. The second trophic level in a lake is-
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes
Ans: (b)

4. Secondary producers are
(a) Herbivores
(b) Producers
(c) Carnivores
(d) None of the above
Ans: (d)

5. What is the percentage of photo synthetically act., radiation (PAR), in the incident solar radiation?
(a) 100%
(b) 50 %
(c) 1-5%
(d) 2-10%
Ans: (b)

6. Distinguish between
(a) Grazing food chain and detritus food chain
(b) Production and decomposition
(c) ‘Upright and inverted pyramid
(d) Food chain and food web
(e) Litter and detritus
(f) Primary and secondary productivity
Ans: (a) Grazing Food Chain (GFC) begins with primary producers or plants and ends in carnivores (tertiary or top carnivores) whereas Detritus Food Chain (DFC) begins with detritus or dead organic matter and it ends in carnivores. In GFC, energy for the food chain comes from sun whereas in DFC, energy for the food chain comes from organic remains or detritus.

(b) Production is the phenomenon in which the energy is produced by the process of synthesis of organic compound from inorganic substances (such as CO₂, H₂O & minerals) utilizing generally the sunlight. It traps energy.
Decomposition refers to the breakdown of complex organic matter into simpler ones. It releases energy.

(c) In upright pyramid (e.g., grassland & cropland ecosystem), biomass or number of organisms or amount of energy decreases
on moving to upper trophic levels while in an inverted pyramid (eg. tree ecosystem) these quantities tend to increase on going to successive trophic levels.

(d) A food chain is a sequence of different types of organisms by which the flow of energy occurs from one trophic level to another whereas food web is the network of various food chains inter-connected to each other. Food webs increase adaptability and competitiveness of the organisms.

(e) Litter is the dead organic material fallen on the surface of the soil like leaves, remains of animals and excreta. Detritus is the dead organic matter found below the soil surface which is eaten up by the detritivores or broken down by decomposers.

(f) Primary productivity is the rate of synthesis of biomass or energy fixation by the plants. It is comparatively quite high.
Secondary productivity is the rate of synthesis of biomass by consumers (herbivores and carnivores). It is small and decreases with rise of trophic level.

7. Describe the components of an ecosystem.
Ans: The components of an ecosystem are as follows :

1. Abiotic components or non living components : These include inorganic substances or minerals (standing state or standing quality), organic substances and different climatic conditions like temperature, pH, light, etc.
2. Biotic components or living components :

(a) Autotrophs or producers which have capacity to manufacture their own food or which can fix radiant energy of sun into chemical energy, e.g., green plants and photosynthetic bacteria.

(b) Heterotrophs or consumers which are unable to manufacture their own food and depend upon other organisms for their food. These are of following types:

• Primary consumers or herbivores which depend upon producers or green plants for their food.
• Secondary consumers or carnivores which live upon herbivores.
• Top consumers or top carnivores which live upon secondary consumers.

(c) Decomposers or microconsumers decompose dead organic substances of producers and consumers into simple substances and thus continue mineral cycles, e.g., bacteria, fungi, actinomycetes etc.

8. Define’ecological pyramids and describe with examples, pyramids of number and biomass.
Ans:  Ecological pyramid is a graphical method to show the number of organisms or biomass or amount of energy present at different trophic levels. Pyramid of number: Number of individuals at each trophic level is shown in pyramid. The pyramid of number (for example of a grassland) is upright. In this there is a decrease in the number of organisms starting from primary producers (plants) to top consumers (carnivores). Pyramid of biomass : Pyramid of biomass is graphic representation of amount of biomass per unit area sequence wise in rising trophic levels with producers at the base and top carnivores at the apex. Pyramids of biomass of a tree or . grassland ecosystem are upright and the pyramid of a pond ecosystem is inverted.

9. What is primary productivity? Give brief description of factors that affect primary productivity.
Ans: Primary productivity of an ecosystem is the amount of energy fixed or biomass synthesized by primary producers or green plants per unit area per unit time during photosynthesis. Factors affecting primary productivity are –
-Plant species inhabiting a particular area
-Sunlight
-Temperature
-Soil water
-Nutrients
lit deserts, sunlight is abundant but water is scarce or nutrients are lacking. Therefore, in such areas, water & nutrients supply become the limiting factors.

10. Define decomposition and describe the processes and products of decomposition.
Ans: The process by which decomposers break down complex organic remains (dead plants, animal remains and excretions) into inorganic substances like carbon dioxide, water and nutrients is called decomposition. The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralisation. Detritivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation.

By the process of leaching, water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.

Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. The process is called as catabolism.

All the above steps in decomposition operate simultaneously on the detritus. Humification and mineralisation occur during decomposition in the soil.

Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients.

The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.

11. Give an account of energy flow in an ecosystem.
Ans: Flow of energy in an ecosystem is unidirectional. The ultimate source of energy is sun. The solar energy is captured by the green plants which utilize it in synthesizing their own food. The energy fixed by the green plants is transferred to herbivores which feed on them. The energy is then transferred to higher trophic levels (carnivores). At every step, considerable amount of energy is lost. According to 10% law, only 10% of total energy stored in a trophic level is transferred to the next trophic level of a food chain.

12. Write important features of a sedimentary cycle in an ecosystem.
Ans: The movement of nutrient elements through various components of an ecosystem takes place by a biogeochemical cycle. It is of 2 types – gaseous and sedimentary. A nutrient that does not enter the atmosphere easily is said to have a sedimentary cycle. Sedimentary cycle involve cycling of sulphur, phosphorus etc. which are located in earth’s crust.
Phosphorus is a very important element as it is present in various substances found in living beings. The cycling of phosphorus in an ecosystem occurs in such a way that plants obtain it from soil or rocks. The animals or primary consumers obtain it from plants. Secondary consumers or carnivores take it from herbivores while omnivores (like man) receive it both from plants and animals. Phosphorus present in organisms is also released during decomposition.

13. Outline salient features of carbon cycling in an ecosystem.
Ans:  Carbon is an important constituent of living matter. Green plants take it in the form of C02 from atmosphere and fix it as carbohydrates. Carbon which is also present in proteins, fats etc. is transferred to the organisms of other trophic levels. Apart from being released in atmosphere as C02 during respiration, carbon is also released in atmosphere through burning of wood, fossil fuel and decomposition of organic matter by microbes.

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