NCERT Solutions for Class 12 Biology Chapter 16: Environmental Issues

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    1. What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
    Ans.The various constituents of domestic sewage:
    (i) Dissolv ed salt such as nitrates, phosphates etc. from detergents.
    (ii) Toxic metal ions from paints, varnishes etc.
    (iii) Biodegradable organic matter from kitchen and toilet.
    (iv) Pathogenic microbes in the faceal matter.
    Effects of sewage discharge on river:
    (i) A sharp decline is dissolve oxygen. Low oxygen levels in the water causes death of fisher and other marine creatures.
    (ii) Algal bloom which results from the presence of organic matter in water which causes:
    (a) Deterioration of the water quality.
    (b) Fish mortality.
    (c) Toxicity to human and animals.
    (iii) Biological magnification of few toxic substances causing harmful effects in living species.
    (iv) Destruction of flora and fauna of the 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.
    Yes, waste can be easily reduced by use of the above materials. Wastage of paper can be minimized by writing both sides of the paper and by using recycled paper. Plastic and glass waste can also reduced by recycling and reusing.
    Non-biodegradable wastes such as plastic, metal, broken glass etc. are difficult to decompose because microorganism do not have ability to decompose them.

    3. Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
    Ans. 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) Eruption 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) Dev eloping substitutes for chlorofluorocarbons. 

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

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

    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: Eutrophication may be defined as the inorganic nutrient enrichment of natural waters, leading to an increased production of algae and macrophytes.
    (b) Biological magnification: Biological magnification is the increase in concentration of toxic substances such as DDT in subsequent tropical level.
    (c) Groundwater depletion: Groundwater has been extensively used for irrigation, industrial waste and household use. This has lead to serious reduction of underground water levels.
    Ways for its replenishment:
    (i) Rain water harvesting by digging holes in the ground and storing them during rainy season.
    (ii) Sewage and factory wastes should be treated to clean them before their release into water source.

    6. Why does ozone hole forms over Antarctica? How will enhanced ultraviolet radiation affect us?

    Ans. Ozone hole forms over Antarctica because of increase of accumulation of ozone depleting substances like CH4N4O, chlorofluorocarbons (CFCS) released into atmosphere.
    Enhanced ultraviolet radiation causes:
    (i) Skin cancer
    (ii) Blindness and cataract in eyes
    (iii) Weak immune system
    (iv) Higher frequency of mutation. 

    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 attempt to 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 with her three daughters and more than 360 of other Bishnois lost their lives in saving trees and 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.
    (vi) 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 wastes: The radioactive wastes are the material that is either intrinsically radioactive or has been contaminated by the radioactivity. The radioactive waste nuclear research, coal and rare-earth mining etc.

    (b) Defunct ships and e-wastes: The defunct ships are the dead ships that are no longer in use. These shops are a source of various toxicants such as asbestos, lead, mercury etc.
    e-waste is any electrical or electronic equipment that has been discarded or is of no use. The use of electronics which are destined for refurbishment, reuse, resale, through material recovery or disposal are also considered e-waste.

    (c) Municipal solid wastes: It is commonly known as trash or garbage. It consists of everyday item discarded by public such as kitchen waste, papers, bottles, batteries etc.

    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.
    All these efforts have significantly improved the air quality of Delhi that recorded a substantial fall in CO2 and SO2 level in the city

    11. Discuss briefly the following:
    (a) Greenhouse gases
    (b) Catalytic converter
    (c) Ultraviolet B

    Ans. (a) Greenhouse gases: Greenhouse gases are the gases that absorb and emits infrared radiation. The greenhouse gases trap and emit infrared radiation. The greenhouse gases trap heat in the earth’s atmosphere and warm the planet. CO2, NO4, CH3, O3 CFCs and water vapours are collectively known as greenhouse gases.

    (b) Catalytic Converted: It is an antipollution device, used in an automotive exhaust system that contains a catalyst for that convert pollutant in the exhaust gases, such as CO, unturned hydrocarbons and oxides of nitrogen into harmless compounds.

    (c) Ultraviolet B: It is a part of UV-radiation of wavelength of 280-320 nm. Ozone layer absorbs 50% of UV-B and protects us from harmful effects.
    It damages the DNA and causes:

    1. Early ageing of skin.
    2. Various kinds of skin cancer.
    3. Inflammation of cornea, cataract etc. 

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