NCERT Solutions for Class 12 Biology Chapter 16 Environmental Issues

Here we provide NCERT Solutions for Class 12 Biology Chapter 16 Environmental Issues for English medium students, Which will very helpful for every student in their exams. Students can download the latest NCERT Solutions for Class 12 Biology Chapter 16 Environmental Issues pdf, free NCERT solutions for Class 12 Biology Chapter 16 Environmental Issues book pdf download. Now you will get step by step solution to each question.

NCERT Solutions for Class 12 Biology Chapter 16 Environmental Issues

Question 1.
What are the various constituents of domestic sewage ? Discuss the effects of sewage discharge on a river.
The domestic sewage contains every-thing that goes down the drain into the sewer of the house. The various constituents of domestic sewage are suspended solids, colloidal particles, pathogenic contaminants and dissolved materials. Suspended solids are sand and silt. Colloidal particles include clay, faecal matter, fine fibres of paper and cloth. Pathogenic contaminants are eggs of coliforms and enterococci. Dissolved materials includes inorganic nutrients such as nitrates, phosphates, ammonia, sodium and calcium. Effects of sewage discharge on a river :

  • Water becomes unfit for bathing and drinking and also for domestic or industrial use as it becomes colored, turbid with a lot of particulate matter floating on water.
  • The domestic sewage adds nitrates and phosphates into the river. These nitrates and phosphates encourage a thick bloom of blue green algae, which depletes the oxygen content of the water during night. This suffocates the fish and other aquatic life. Consequently river become highly polluted.

Question 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?
Plastic containers, paper, electronic goods, left over food, food package, disposable glasses, cup plates, polythenes, excreta, soap and detergent waste are the wastes that one can generate at home, school or during trips to other places. Yes, we can easily reduce waste through judicious use of material by changing our habits & life styles.
Out of these, polythene and plastic material are hard to dispose off as they are non- biodegradable and they can be recycled back.

Question 3.
Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
Green house effect is the progressive, gradual warming of the earth’s atmosphere caused by the insulating effect of carbon dioxide and other green house gases that have proportionately increased in the atmosphere. The green house effect disturbs the way the earth’s climate maintains the balance between incoming and outgoing energy by allowing short-wave radiation from the sun to penetrate through to warm the earth, but preventing the resulting long-wave infrared radiation from escaping back into the atmosphere. There is concern that increasing concentration of green house gases, including carbon dioxide, methane, and man made chlorofluorocarbons, may enhance the greenhouse effect and cause global warming.
Effects of global warming are :

(i) Warming of atmosphere will significantly increase its moisture carrying capacity. While the troposphere warms up, the stratosphere will cool down. This would cause extensive changes in precipitation patterns due to changed pattern of air- mass movements. Besides, the frequency of droughts, floods, etc., is estimated to increase substantially. The climate change will increase threats to human health, predominantly in tropical and subtropical countries, due to change in ranges of disease vectors, water-borne pathogens, etc.

(ii) The global warming may contribute to sea level rise due to the thermal expansion of oceans as it warms, and melting of glaciers and Greenland ice sheets. A rise of even half a meter in sea level would profoundly affect human population, one-third of which lives within 60 km of a coastline. Numerous low-lying islands may be submerged. Inundation of coastal salt marshes and estuaries may deprive of many important birds and fishes, their breeding grounds, forcing their extinction.
Strategies to deal with global warming :

  • Complete replacement of chlorofluoro-carbon with substitutes that have little effect on ozone and global warming.
  • Increasing vegetation cover of forests for photosynthetic utilisation of Co2.
  • Reduction in use of nitrogen fertilisers and instead relying more on nitrogen fixation.
  • Limiting use of fossil fuels by developing alternate sources of energy, e.g., solar energy, wind energy.
  • Increasing use of alternative, renewable, nonpolluting sources of energy like solar energy, wind energy, hydropower etc.

Question 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
(a) – (ii); (b) – (i); (c) – (iii); (d) – (iv).

Question 5.
Write critical notes on the following :
(a) Eutrophication
(b) Biological magnification
(c) Groundwater depletion and ways for its replenishment
(a) Eutrophication : Eutrophication is the phenomenon of nutrient enrichment of a water body that initially support a dense growth of plant and animal life. It is caused by run-off from fertilised fields, sub-urban lawns, feed lots and detergent rich sewage. Organic loading or occurrence of excess organic matter occurs inside water. The rapid growth of water plants especially the algae, is called bloom. They cut off light from submerged plants and latter die. This decreased oxygen putrefaction further decreases dissolved oxygen replenishment inside water. Blue green algae present in the bloom also release toxins. Both toxicity and decreased oxygen level kill aquatic animals.

(b) Biological magnification : Industrial wastes released into water contain toxic substances, such as arsenic, cadmium, lead, zinc, copper, mercury, and cyanides, besides some salts, acids and alkalies. All these materials can prove harmful for our health.
NCERT Solutions for Class 12 Biology Chapter 16 Environmental Issues 5.1
They may reach human body directly with contaminated food or indirectly by way of plants and other animals. Concentration of the toxic materials increases at each trophic level of a food chain. This is called biological magnification. River water may have a very low concentration of DDT, but the carnivorous fish in that river may contain high concentration of DDT and become unfit for eating by man. Mercury discharged into rivers and lakes is changed by bacteria to the neurotoxic form called methyl mercury. The latter is highly poisonous and may be directly absorbed by fish.

(c) Groundwater depletion and ways for its replenishment : Groundwater depletion is defined as long-term water-level decline caused by sustained groundwater pumping. The volume of ground water in storage is decreasing in many areas of the world in response to pumping. Some of the negative effects of groundwater depletion include increased pumping costs, deterioration of water quality, reduction of water in streams and lakes.
Some ways for water replenishment are :

  • Reduction in consumption : Sprinkler and subsurface irrigation techniques reduce the amount of water used in irrigation.
  • Rain water harvesting : Rain water collected over roofs is allowed to pass into ground through deep water pipes.

Question 6.
Why does ozone hole forms over Antarctica? How will enhanced ultraviolet radiation affect us?
A large amount of ODS (Ozone Depleting Sub-stances) like CFCs, N2O, halons, SO2, CH4, Cl-are released by advanced countries like USA, Japan, European countries. These are released in stratosphere, drift towards poles and reach there before the coming of winter. During winter (temp. 85°C) ice clouds are formed over Antarctica and no sunrise is received in polar areas. It catalyses release of Cl from CFCs. With the coming of spring season, Cl reacts with ozone in the presence of sunlight and converts 03 into 02 causing ozone depletion/thining of ozone shield in stratosphere called ozone hole. This hole disappears in summer due to free mixing of air ofAntarctica with therestofthe global air. Effect of Enhanced UV Radiation, (i) Snow blindness or inflammation of cornea (ii) Damage of skin cells and development of skin cancer, (iii) Damage to nucleic acids and proteins, (iv) Reduced immunity (v) Higher number of cataracts in humans.

Question 7.
Discuss the role of women and communities in protection and conservation of forests.
In 1731, a Bishnoi women Amrita Devi showed exemplary courage by hugging a tree to prevent its cutting. Her three daughters and hundreds of other Bishnois followed her. They were killed by soldiers of king of Jodhpur. This movement forced the king to abandon cutting of trees. Later ‘Chipko Movement’ was started by Sundar Lai Bahuguna and others to prevent the cutting of trees.

Question 8.
What measures, as an individual, you would take to reduce environmental pollution?
To reduce environmental pollution, we should change our habits and lifestyle so as to reduce the use of disposable materials. We should use preferably those items which can easily be recycled and also minimise the use of fossil fuels. We should also take measures to improve the quality of air by using CNG gases wherever possible instead of using diesel or petrol. We should also use catalytic converter in our vehicles.

Question 9.
Discuss briefly the following :
(a) Radioactive wastes
(b) Defunct ships and e-wastes
(c) Municipal solid wastes
(a) Radioactive Waste. They are nonusable discards which possess radioactivity. Radioactive wastes are of three types: —

  • Wastes with low level radioactivity: Coolant water of atomic reactors and pond water used for cooling spent fuel contain very small amount of radioactivity. This, however, undergoes biomagnification.
    Irradiation centres, radiotherapy units and laboratories also produce wastes with low level radioactivity,
  • Wastes with intermediate level radioactivity: They are radioactive wastes of many ores which are separated during refinement of minerals,
  • Wastes with high level radioactivity: Spent fuel of atomic reactors and leakage from reactors have very high level of radioactivity. All wastes with radioactivity have to be handled carefully and dumped 500 m deep in earth or inside sea after placing them inside very thick protective containers.
    Radioactive wastes are highly dangerous to human beings, animals, microbes and vegetation. They kill all of them. Loss of hair, nails appearance of deformities, cancers and genetic defects appear due to mutations.

(b) Defunct ships and e-wastes – Defunct ships also contribute to solid wastes. Such ships are broken down for scarp metal in developing countries like India. These defunct ships are the source of toxicants like asbestos, polychlorinated biphenyls, tributylin, lead, mercury, etc. The workers get exposed to these chemicals and coastal area in the vicinity of ship breaking yard gets polluted. Irreparable computers and other electronic goods are responsible for electronic wastes or e-wastes. Such wastes can only be buried in land fills or incinerated. Developed countries export the e-wastes to developing countries where metals like copper, iron, silicon, nickel and gold are recovered from e-wastes by recycling process. In the process, workers get exposed to these harmful toxic substances.

(c) Municipal solid wastes – Municipal solid wastes include domestic/kitchen wastes, market wastes, sweepings, wastes, from commercial complexes, rubbish, hospitals, slaughter houses, livestock/poultry wastes and trash like waste metals e.g., cans, plastic, pet bottles, polyethylene carry bags etc. Hospital wastes include vials, plastic and glass bottles, syringes, needles, organic wastes, chemicals and a lot of pathogen carriers. Hospital and domestic wastes are thus a source of variety of pathogens. Municipal wastes are partly degradable and partly nondegradable. Burning reduces the volume of wastes although it is generally not burnt to completion and open dumps often serve as breeding ground for rats and flies.

Question 10.
What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
Under the direction of Supreme Court of India, the State Government of Delhi took the following measures to improve the quality of air:

  • Switching over the entire fleet of public transport buses from diesel to CNG (Compressed Natural Gas) by the end of 2002.
  • Phasing out of old vehicles.
  • Use of unleaded petrol.
  • Use of low sulphur petrol and diesel.
  • Use of catalytic converters in vehicles.
  • Application of Euro II norms for vehicles.

Because of above mentioned measures adopted by the Government the air quality of Delhi has improved with a substantial fall in S02, CO, Nox level between 1997-2005.

Question 11.
Discuss in brief the following:
(a) Green house gases
(b) Catalytic converter
(c) Ultraviolet B
(a) Green house gases : The gases which are transparent to solar radiation but retain and partially reflect back long wave heat radiations are called green house gases. Green house gases are essential for keeping the earth warm and hospitable. They are also called radiatively active gases. They prevent a substantial part of long wave radiations emitted by earth to escape into space. Rather green house gases radiate a part of this energy back to the earth. The phenomenon is called green house flux. Because of green house flux, the mean annual temperature of earth is 15°C. In its absence it will fall to – 18°C. However, recently the concentration of green house gases has started rising resulting in enhanced green house effect that is resulting in increasing the mean global temperature. It is called global warming. A regular assessment of abundance of green house gases and their impact on global environment is being made by IPCC (Intergovernmental Panel on Climate Change). The various green house gases are CO2 (warming effect 60%), CH4 (effect 20%) , chlorofluorocarbons or CFCs (14%) andT nitrous oxide (N2O, 6%). Others of minor significance are water vapours and ozone.

(b) Catalytic converter: Catalytic converters are devices that are fitted into automobiles for reducing the emission of gases. These have expensive metals (platinum – palladium and rhodium) as catalysts. As the exhaust passes through the catalytic converters, unburnt hydrocarbons are converted into CO2 and H2O and carbon monoxide and nitric oxide are changed to CO2 and N2 respectively. Vehicles fitted with catalytic converters should be run on unleaded petrol as leaded petrol would inactivate the catalyst in the converters.

(c) Ultraviolet B – UV-B having 280-320nm wavelength. Their harmful radiations penetrate through the ozone hole to strike the earth. On earth, these can affect human beings and other animals by causing :

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

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