NCERT Class 12 Biology Chapter 16 Environmental Issues

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NCERT Class 12 Biology Chapter 16 Environmental Issues

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Environmental Issues

Chapter: 16

BIOLOGY

UNIT – V ECOLOGY AND ENVIRONMENT

TEXT BOOK QUESTIONS

Q. 1. What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.

Ans: Domestic sewage has 99% of water and 0.1% impurities. 0.1% Impurities in domestic sewage are suspended solids e.g. sand, silt and clay, colloidal material e.g. fecal matter, bacteria, cloth and paper fibers, dissolved materials eg. organic compounds and salts like nitrate, ammonia, phosphate, sodium, calcium. 

Effects of sewage discharge on a river are:

(i) Domestic Sewage has pathogenic microorganisms and its disposal into water without proper treatment can cause outbreak of diseases like dysentery, typhoid, jaundice, cholera etc.

(ii) Domestic sewage increases the levels of BOD.

(iii) Algal bloom.

(iv) Eutrophication.

Q. 2. List all the wastes that you generate, at home, school or during your Trips to other places, could you very easily reduce? Which would be Difficult or rather impossible to reduce? 

Ans: It consists of paper, food wastes, plastics, glass, metals, rubber, leather, textile etc.

Paper, food wastes are easy to reduce. Non- biodegradable wastes such as plastic, metal, broken glass, etc. are difficult to decompose because micro-organisms do not have the ability to decompose them.

Q. 3. Discuss the causes and effects of global warming. What measures need to be taken to control global warming?

Ans: Global warming occurs due to increased level of greenhouse gasses in the atmosphere. Greenhouse gasses are carbon dioxide, methane, CFC, nitrous oxide and water vapor.

Effects of Global Warming:

(i) Increase in level of greenhouse gasses has caused heating of Earth leading to global warming.

(ii) Temperature of Earth has increased by 0.6°C.

(iii) Ozone hole: It is the area above Antarctica (shown in purple color] where the ozone layer is thinnest.

(iv) Odd climatic changes (e.g. EL Nino effect).

(v) Increased melting of polar ice caps and Himalayan snow caps. 

(vi) Rise in sea level that can submerge many coastal areas. 

Following measures can be used to decrease the global warming:

(i) Decreasing the use of fossil fuel.

(ii) Improving efficiency of energy usage. Reducing deforestation.

(iii) Planting trees.

(iv) Slowing down the growth of human population.

(v) Reduce emission of greenhouse gasses into the atmosphere.

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

Column A	Column B
(a) Catalytic converter	(i) Particulate matter
(b) Electrostatic precipitator	(ii) Carbon monoxide and nitrogen oxides
(c) Earmuffs	(iii) High noise level
(d) Landfills	(iv) Solid wastes

Ans: 

Column A	Column B
(a) Catalytic converter	(ii) Carbon monoxide and nitrogen oxides
(b) Electrostatic precipitator	(i) Particulate matter
(c) Earmuffs	(iii) High noise level
(d) Landfills	(iv) Solid wastes

Q. 5. Write critical notes on the following:

(a) Eutrophication.

Ans: Eutrophication is excessive growth of algae, plants and animal in water bodies due to nutrient enrichment mostly nitrogen and phosphorous.

(b) Biological magnification.

Ans: Biomagnification is increase in concentration of the toxicant at successive trophic levels in the food chain. It occurs because a toxic substance accumulated by an organism cannot be metabolized or excreted, and is passed on to the next higher trophic level in the food chain. E.g. If DDT concentration is 0.003 ppb (parts per billion) in water then it reaches 25 ppm (parts per million) in fish-eating birds through Biomagnification. 

(c) Groundwater depletion and ways for its replenishment.

Ans: Ground water depletion and ways for its replenishment:

(i) Ground water is depleting due to deforestation, water pollution and excessive water wastage etc. 

(ii) Measures for replenishing ground water are rain water harvesting, preventing deforestation and plantation of more trees. 

Q. 6. Why ozone hole forms over Antarctica? How will enhanced ultraviolet Radiations affect us?

Ans: UV rays act on CFCs in stratosphere releasing Cl atoms. Cl degrades ozone releasing molecular oxygen. Ozone depletion in the stratosphere has resulted in formation of a large area of thinned ozone layer called ozone hole. It is particularly marked over the Antarctic region.

OZONE HOLE results in the increase of UV-B radiations.

(a) UV-B damages DNA and mutation may occur.

(b) UV-B causes aging of skin and skin cancer. 

(c) Snow-blindness.

(i) Cornea in human eye absorbs UV-B radiation. This causes inflammation of cornea called snow-blindness, cataract and corneal damage. 

Q. 7. Discuss the role of women and communities in protection and conservation of forests.

Ans: People’s Participation in Conserva- tion of Forests ― 

(i) Bishnoi community and Amrita Devi of Jodhpur in Rajasthan.

(ii) Chipko Movement of Garhwal Himalayas.

(iii) Joint Forest Management (JFM).

Q. 8. What measures, as an individual, you would take to reduce environmental pollution?

Ans: Methods to control environmental pollution are: 

(i) Proper maintenance of automobiles and phasing out of old vehicles. 

(ii) Use of lead free petrol and diesel.

(iii) Use of low Sulphur petrol and diesel.

(iv) Catalytic converters. 

(v) Use of compressed natural gas [CNG] instead of petrol and diesel.

(vi) Application of stringent pollution-level norms for vehicles to reduce the sulfur and aromatic content in petrol and diesel fuels.

Q. 9. Discuss briefly the following:

(a) Radioactive wastes.

Ans: Radioactive wastes: It is most potent pollutant. Radioactive wastes cause pollution due to 

(i) Accidental leakage of radioactive materials from nuclear energy plants e.g. Three Mile Island and Chernobyl incident 

(ii) Unsafe disposal of radioactive wastes. Radiations cause mutations, cancer and death at fatal doses. It should be stored in shielded containers and then buried 500 m deep in earth.

(b) Defunct ships and e-wastes.

Ans: Defunct ships and e-wastes: Defunct ships and E-wastes generated in the developed world are exported to developing countries like China, India where metals like copper, iron. silicon, nickel and gold are recovered during recycling process. Recycling involves manual participation which exposes workers to toxic substances.

(c) Municipal solid wastes.

Ans: Municipal solid wastes are wastes from homes, offices, stores, schools, hospitals etc that are collected and disposed by the municipality. It consists of paper, food wastes, plastics, glass, metals, rubber, leather, textile etc. Methods of solid waste disposal are Open Burning and Sanitary landfills.

Q. 10. What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?

Ans: Methods to control vehicular pollution are:

1. Proper maintenance of automobiles and phasing out of old vehicles.

2. Use of lead free petrol and diesel.

3. Use of low Sulphur petrol and diesel.

4. Catalytic converters.

5. Use of compressed natural gas [CNG] instead of petrol and diesel. 

6. Application of stringent pollution-level norms for vehicles to reduce the sulfur and aromatic content in petrol and diesel fuels.

Air quality is worsening in Delhi.

Q. 11. Discuss briefly the following: 

(a) Greenhouse gasses.

Ans: Greenhouse gasses: Greenhouse gasses absorb long wave infrared radiations from Earth and emit it again towards the earth. The cycle is repeated many times till earth surface has no infrared radiation to emit. This heats the earth surface and leads to global warming. Greenhouse gasses are CO2 (60%), methane (20%), CFC or chlorofluoro-carbons (14%), N20 (6%) and water vapors.

(b) Catalytic converter.

Ans: Catalytic converter: Catalytic converters having platinum-palladium and rhodium as the catalysts are fitted into automobiles for reducing emission of poisonous gases.Exhaust gasses pass through the catalytic converter. Unburnt hydrocarbons are converted into carbon dioxide and water. Carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.

(c) Ultraviolet B.

Ans: Ultraviolet-B: 

(i) UV-B damages DNA and cause mutation.

(ii) UV-B causes aging of skin and skin cancer.

(iii) Cornea in human eye absorbs UV-B radiation. This causes inflammation of cornea called snow-blindness, cataract and corneal damage.