NCERT Solutions for Class 12 Biology Chapter 16 - Environmental Issues

Question 1:

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


Constituents of domestic sewage. It mainly consists of biodegradable organic matter :
1. It results in eutrophication.
2. Suspended solids e.g., sand, silt and clay.
3. Colloidal materials. They are both organic and inorganic faecal matter e.g. bacteria, cloth and paper fibre.
4. Dissolved materials. e.g. nutrients (nitrates, ammonia, phosphates, sodium and calcium). Effects of Sewage discharge on a river:
1. Water ways become biologically barren. Aquatic organisms can tolerate poisons and other pollutants only in low concentrations. Excess may prove lethal. Different organisms have different levels of tolerance or sensitivity to various effluents or poisons and toxicity of most poisons is also affected by environmental factors such as temperature, –pH, oxygen contents, calcium contents etc. Water ways polluted with zinc and lead often become biologically barren.
2. Diseases caused by polluted water.
(i) Bacterial diseases. Cholera, Typhoid, Diarrhoea, Dysentery.
(ii) Viral diseases. Jaundice, Polio etc.
(iii) Protozoanal diseases. Diseases associated with stomach and intestines e.g. Amoebic dysentery, Giardiasis etc.
(iv) Helminthic diseases. Infection of some intestinal parasites like Ascaris lumbricoides is through drinking water only. Guinea worm diseases is through Cyclops present in the drinking water. Through contaminated water they reach to another host i.e. man.

Question 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 ?


List of wastes:
1. Papers, clothes, polythene bags
2. Disposable crockery,
3. Aluminium foil, cans
4. Leftover of tiffins
5. Wood
6. Sewage
Wastes which can be reduced:
1. Papers, clothes,
2. Left over of tiffins.
Wastes which cannot be reduced:
1. Aluminium foil cans 2. Disposable crockery 3. Polythene bags

Question 3:

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


Global warming. Increase in the level of greenhouse gases has led to considerable heating of earth leading to global warming. During the past century, the temperature of earth has increased by 0.6°C, most of which during the last three decades. It is estimated that average global temperate may rise 1.4 to 5.8°C in the year 2100.
Effects of global warming
1. Effect on weather and climate. (i) The average temperature of earth may increase by 1.4° to 5.8°C by the year 2100.
(ii) Winter precipitation may decrease at lower altitude.
(iii) Frequency of draughts, floods may increase.
(iv) Climatic change is threat to human health in tropical and subtropical countries.
2. Sea level change. Sea level had been raised by 1 to 2 mm per year during the 20th century. It is predicted that by the year 2100, the global mean sea level can increase up to 0.88 m over the 1990 level. The global warming may contribute to sea level rise due to the thermal expansion of ocean.
3. Effect on range of species distribution. Vegetation may extend 250-600 km poleward with a global rise in temperature by 2 to 5°C during 21st century.
4. Effect on food production. Increased temperature will cause eruption of plant diseases and pests and vast growth of weeds. Strategies to deal with Global Warming Some of the strategies that could reduce the global warming by stabilizing atmospheric concentrations of greenhouse gases include:
1. Reducing the greenhouse gas emissions by limiting the use of fossil fuels, and by developing alternative renewable sources of energy (e.g. wind energy, solar energy, etc.).
2. Increasing the vegetation cover, particularly the forests, for photosynthetic utilization of CO2.
3. Minimizing the use of nitrogen fertilizers in agriculture for reducing NO2 emissions.
4. Developing substitutes for chlorofluorocarbons.
5. Apart from the above litigation strategies, adaptations to address localized impacts of climate change will be necessary.

Question 4:

Match the items in column A and column B :


1. – (b), 2. – (a), 3. – (c ), 4. – (d)

Question 5:

Write critical notes on Eutrophication.


Eutrophication. The process by which a body of water becomes barren either by natural means or by pollution, extensively rich in dissolved nutrients. It results in the increased primary productivity that often leads to seasonal deficiency in dissolved oxygen.
Algal bloom. Phosphorus and nitrates dissolved in water act as nutrients and accelerate the growth of algae that may form a mat on the water surface. It is termed algal bloom.
Effects.. The algae use oxygen at night and may deoxygenate the water enough to kill the fish and other animals. The algal mat at the water surface may block light to the submerged plants. The algae may die and sink, and feed the oxygen-consuming bacteria. They may be pushed on to the shore by wind and decompose, releasing foul gases, such as hydrogen sulphide. Silt and decaying matter may accumulate and finally fill the lake or pond. This process is called senescence. It is a natural stage in the change of a lake into dry land and it becomes barren, ultimately death of lake occurs.

Question 6:

Write critical notes on Biological magnification.


Biological magnification (Biomagnification). The phenomenon in which the harmful pollutants (such as pesticides) enter the food chain and get concentrated more and more at each successive trophic level of organisms is called biological magnification. This phenomenon is well known for mercury and DDT. Figure on the side shows biomagnification of DDT in an aquatic food chain. Zooplankton (tiny floating animals) in the food chain, accumulated modest levels of DDT. However, small fish, forming the next level of the food chain, must eat zooplankton several times their own weight and thus they accumulated more of DDT.
In this manner, the concentration of DDT magnified at successive trophic levels, starting with 0.003 ppb (ppb = parts per billion) in water it ultimately reached 25 ppm (ppm = parts per million) in fish-eating birds.Effect. High concentrations of DDT disturb calcium metabolism in birds. It causes thinning of egg shell and their premature breaking. Thus, there is decline in bird population.

Question 7:

Write critical notes on Ground water depletion and ways for its replenishment.


Ground water depletion and ways for its replenishment. Underground water is more pure and safe for drinking. It is getting polluted particularly in industrial towns. The common sources of underground water pollution are sewage and industrial effluents spilled over the ground. The fertilizers and pesticides used in fields also act as pollutants. Pollution is also increased due to seepage from refuse dumps, septic tanks and seepage pits.
Method to control. Sewage and factory wastes should be treated to clean them before their release into water sources.

Question 8:

Why ozone hole forms over Antarctica? How will enhanced UV radiations affect us?


Ozone hole. During the period 1956-1970 the spring time O3 layer thickness above Antarctica varied from 280-325 Dobson unit. Thickness was sharply reduced to 225 DU in 1979 and 136 DU in 1985. Antarctic air is completely isolated from rest of world by natural circulation of wind called as polar vertex. The decline in spring time, ozone layer thickness is called ozone hole. It was first noted in 1985 over Antarctica.
Effects of UV radiations on human.
1. In humans, the increase UV radiation increases the incidence in cancer (including melanoma).
2. Reduces the functioning of immune system.
3. Cornea absorbs UV–B radiations, and a high dose of UV–B causes inflammation of cornea called snow blindness, cataract etc. Exposure may permanently damage cornea and cause cataract.

Question 9:

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


Role of women and communities in protection and conservation of forests:
1. In 1731, Bishnoi community led by women Amrita Devi obstructed the cutting of trees by hugging the tree and asked the workers of king to cut her before cutting the tree. Her three daughters and hundreds of other Bishnois lost their lives in saving trees.
2. Chipko movement started by Chandi Prasad Bhatt and Sunder Lal Bahuguna of Silyara in Tehri region, when workers of contractor were not allowed to cut the trees by village people by hugg ing around them.

Question 9:

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


Role of individual in reducing pollution. 1. Use of unleaded petrol or CNG in vehicles as fuel.
2. Use of reformulated gasoline to save ozone in the atmosphere.
3. Use of power generators in residential areas should be avoided. 4. Plantation of trees.
5. Excessive and unplanned use of fertilizers should be avoided.
6. Biodegradable material should be used.
7. Donot blow horn with jarring sound.
8. Radio, transistors, T.V., Music system should be kept at low volume to control noise pollution.

Question 10:

Discuss briefly the radioactive wastes.


Radioactive wastes. Radioactive wastes are of three types depending on the amount of radioactivity.
1. Low level radioactive wastes.
2. Intermediate level radioactive wastes.
3. High level radioactive wastes.
Use of nuclear energy has two most serious problems. The first is accidental leakage and the second is safe disposal of radioactive wastes. Wastes from atomic power plants come in the form of spent fuels of uranium and plutonium. People working in such power plants, nuclear reactors, fuel processors, etc. are vulnerable to their exposure. These also undergo biological magnification and may reach to 75,000 times in birds.
Radio isotopes. Many radioactive isotopes like C14, I125, P32 and their compounds are used in scientific researches. The waste water of these research centres contain the radioactive elements which may reach the human beings through water and food chains.
Disposal of radioactive wastes. Such wastes are first concentrated to reduce the volume and then kept for 50-100 years in small ponds within the premises of nuclear power plants. This interim storage causes considerable decay of radioactivity and lessening of heat problem. It has been recommended that subsequent storage should be done in suitably shielded containers buried within the rocks, about 500 m deep inside Earth. However, this method of disposal is meeting stiff opposition from the public.

Question 11:

Discuss briefly the defunct ships and e-wastes.


Defunct ships and e-wastes. Defunct ships are a kind of solid waste requiring proper disposal. Such ships are broken down in developing countries because of cheap labour and for scrap metal. They often contain toxic substances such as asbestos, polychlorinated biphenyls, tributyltin, lead and mercury.
Similarly irreparable computers and electronic goods are known as electronic wastes or e-wastes. Most of them are shipped to developing countries for metals like copper, nickel, silicon, gold are recovered by recycling. Recycling the environmental friendly technologies steal the methods for treatment of defunct ships and e-wastes. International treaty called Basel Convention drafted in Basel (Switzerland) was result of great demand from developing countries.

Question 12:

Discuss briefly the municipal solid wastes.


Municipal Solid Wastes. Solid wastes refer to everything that goes out in trash. Municipal solid wastes are wastes from homes, offices, stores, schools, etc. that are collected and disposed by the municipality.
The municipal solid wastes generally comprise paper, food wastes, glass, metals, rubber, leather, textile, etc. Burning reduces the volume of the wastes, although it is generally not complete and open dumps often serve as the breeding ground for rats and flies.
Management of municipal solid wastes.
1. Sanitary landfills were adopted as the substitute for open-burning dumps. In a sanitary landfill, wastes are dumped in a depression or trench after compaction, and covered with dirt everyday.
2. Municipal solid wastes, containing bio-degradable organic wastes, can be transformed into organic manure for agriculture.
3. Sewage sludge and industrial solid wastes are used as land fills.
4. Hazardous metal-containing wastes are used as bedding material for road construction.
5. Other options are incineration of wastes and using emitted heat in electricity generation, and recycling various components of wastes.

Question 13:

Explain any three measures which will control vehicular air pollution in Indian cities.


Some specific measures taken to reduce vehicular air pollution are follows :
1. Use of CNG (Compressed Natural Gas) for its public transport system.
2. Phasing out of old vehicles.
3. Use of unleaded petrol.
4. Use of low sulphur petrol and diesel.
5. Use of catalytic converter in vehicles.
6. Application of Euro II norms for vehicles.
Because of above mentioned steps taken up by the Government, the air quality of Delhi has improved with a substantial fall in carbon monoxide, oxides of sulphur and nitrogen level between 1997-2005.

Question 14:

Discuss briefly the greenhouse effect.


Greenhouse effect. Earth’s temperature is maintained by reradiated infra-red radiations by CO2, CH4, O3, NO and NO2 and slightly by water vapours in atmosphere. These gases prevent heat from escaping to outer space, so are functionally comparable to glass panels of a greenhouse and are called greenhouse gases (GHGs) and called as greenhouse effect. The CO22 is added to atmosphere mainly by burning of fossil fuels, volcanic activities etc.
Greenhouse gases are useful in keeping the earth warm with an average temperature of 15° C. In their absence the surface temperature of earth will be as low as 18° C. This temperature will freeze all water and kill most life. However, excess of greenhouse gases is equally harmful. Over 7 × 1012 kg of CO2 is being added annually to the atmosphere by burning of fossil fuels. As a result CO2 concentration of the atmosphere has risen from 0.028% in 1800 to 0.0359% in 1994.

Question 15:

Discuss briefly the catalytic converter.


Catalytic converter. Catalytic converters, having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing emission of gases. As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively. Motor vehicles equipped with catalytic converter should use unleaded petrol because leaded petrol inactivates the catalyst.
It has been established that installation of catalytic convertors can slash carbon monoxide emission from 90 grams to 3.4 grams per mile run. So if half the vehicles on Delhi and Mumbai roads are made to install such catalytic converters, then total CO emission in India can be reduced by 70 per cent.

Question 16:

Discuss briefly the ultraviolet B radiations.


Ultraviolet-B radiations. These are high energetic UV-radiations which are mostly blocked by the ozonosphere located in the stratosphere of the atmosphere. But due to increased production of ozonedepleting substances (ODS) like CFCs, halons, etc., the ozone shield is becoming thinner and thinner. This is increasing the amount of UV-ow does this affect the plants?