NCERT Exemplar Problems Class 12 Biology Chapter 16 Environmental Issues

Multiple Choice Questions
Single Correct Answer Type
1. Non-biodegradable pollutants are created by
(a) Nature (b) Excessive use of resources
(c) Humans (d) Natural disasters
Answer. (c) Non-biodegradable pollutants are created by humans.

2. According to the Central Pollution Control Board, particles that are responsible for causing great harm to human health are of diameter
(a) 2.50 micrometers (b) 5.00 micrometers
(c) 10.00 micrometers (d) 7.5 micrometers
Answer. (a) According to CPCB (Central Pollution Control Board) particulate size 2.5 micrometer or less in diameter (PM 2.5) are responsible for causing the greatest harm to human health.

3. The material generally used for sound proofing of rooms like a recording studio and auditorium, etc. is
(a) Cotton (b) Coir (c) Wood (d) Styro foam
Answer. (d) Styro foam is a kind of expanded polystyrene used especially for making food containers used for sound proofing of rooms like a recording studio and auditorium, etc.

4. Compressed Natural Gas (CNG) is
(a) Propane (b) Methane (c) Ethane (d) Butane
Answer. (b) Compressed Natural Gas (CNG) is methane.

5. World’s most problematic aquatic weed is
(a) Azolla (b) Wolffia (c) Eichhomia (d) Trapa
Answer. (c) The world’s most problematic aquatic weed is water hyacinth (Eichhornia crassipes) also called Terror of Bengal. It were introduced into India for their lovely flowers (mauve coloured) and shape of leaves. They grow abundantly in eutrophic (nutrient rich) water bodies. Eichhornia caused havoc by their excessive growth by causing blocks in our water ways and lead to an imbalance in the ecosystem dynamics of the water body. They grow faster than our ability to remove them.

6. Which of the following causes biomagnification?
(a) SO2 (b) Mercury
(c) DDT (d) Both (b) and (c)
Answer. (d) Biomagnification refers to increase in concentration of the toxicant at successive trophic level. This phenomenon is well known for DDT and Hg. In an aquatic food chain concentration of DDT is 0.003 ppb (parts per billion) in water but it can ultimately reaches 25 ppm in fish eating birds through biomagnification. Highest DDT deposition shall occur in birds or sea gull. High concentration of DDT disturb calcium metabolism in birds which causes:
1. Thining of egg shell.
2. Their premature breaking of egg shell.
Thus eventually causing decline in bird population.

7. The expanded form of DDT is
(a) Dichloro diphenyl trichloroethane
(b) Dichloro diethyl trichloroethane
(c) Dichlorodipyrydyltrichloroethane
(d) Dichloro diphenyl tetrachloroacetate
Answer. (a) The expanded form of DDT is dichloro diphenyl trichloroethane.

8. Which of the following material takes the longest time for biodegradation?
(a) Cotton (b) Paper (c) Bone (d) Jute
Answer. (c)

9. Choose the incorrect statement.
(a) The Montreal protocol is associated with the control of emission of ozone depleting substances
(b) Methane and carbon dioxide are greenhouse gases
(c) Dobson units are used to measure oxygen content
(d) Use of incinerators is crucial to disposal of hospital wastes
Answer. (c) The thickness of ozone is measured in terms of Dobson Units (DU). In stratosphere ozone gas is continuously-formed by the action of ultra violet rays on molecular oxygen & also degraded into molecular oxygen.
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10. Among the following which one causes more indoor chemical pollution?
(a) Burning coal (b) Burning cooking gas
(c) Burning mosquito coil (d) Room spray
Answer. (a) Burning coal causes more indoor chemical pollution.

11. The green scum seen in the fresh water bodies is
(a) Blue green algae (b) Red algae
(c) Green algae (d) Both (a) and (c)
Answer. (d) The green scum seen in the fresh water bodies is due to blue green algae and green algae.

12. The loudness of a sound that a person can withstand without discomfort is about
(a) 150 dB (b) 215 dB (c) 30 dB (d) 80 dB
Answer. (d) Green muffler is related to pollution of noise. Noise pollution is measured in decibels (dB). Intensity level of whispering sound is 20-40 dB. Intensity of sound in normal conservation 30-60 dB. Day time sound level in silent zone is 50 dB. Noise become uncomfortable above 80 dB. Sound become hazardous noise pollution at level above 80 dB.

13. The major source of noise pollution, worldwide is due to
(a) Office equipment
(b) Transport system
(c) Sugar, textile and paper industries
(d) Oil refineries and thermal power plants
Answer. (b) The major source of noise pollution, worldwide is due to transport system.

14. Match correctly the following and choose the correct option:
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The correct matches is
(a) i”C, ii”D, iii”A, iv”B (b) i”A, ii”C, iii”B, iv”D
(c) i”D, ii”A, iii”B, iv”C (d) i”C, ii”D, iii”B, iv”A
Answer. (a)
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15. Catalytic converters are fitted into automobiles to reduce emission of harmful gases. Catalytic converters change unburnt hydrocarbons into (a) Carbon dioxide and water (b) Carbon monoxide (c) Methane (d) Carbon dioxide and methane.
Answer. (a) Catalytic converters are fitted into automobiles for reducing emission of poisonous gases.’ Catalytic converters have expensive metals namely platinum—palladium and rhodium (Pt—Pd and Rh) as catalysts. As the exaust passes through the catalytic converter :
1. Unburnt hydrocarbons are converted into CO2 and H20.
2. Carbon monoxide is changed to CO2.
3. Nitric oxide (NO) is changed to N, gas.
Vehicles equipped with catalytic converters should use unleaded petrol because lead in the petrol inactivates the catalyst.

16. Why is it necessary to remove sulphur from petroleum products?
(a) To reduce the emission of sulphur dioxide in exhaust fumes.
(b) To increase efficiency of automobiles engines.
(c) To use sulphur removed from petroleum for commercial purposes.
(d) To increase the life span of engine silencers.
Answer. (a) To reduce the emission of sulphur dioxide in exhaust fumes is necessary to remove sulphur from petroleum products.

17. Which one of the following impurities is easiest to remove from wastewater?
(a) Bacteria (b) Colloids
(c) Dissolved solids (d) Suspended solids
Answer. (d) Suspended solids impurities is easiest to remove from waste water.

18. Which one of the following diseases is not due to contamination of water?
(a) Hepatitis-B (b) Jaundice (c) Cholera (d) Typhoid
Answer. (a) Sewage from our homes as well as from hospitals are likely to contain many undesirable pathogenic micro-organisms and its disposal into a water without proper treatment may cause outbreak of serious diseases such as:
1. Dysentry, 2. Typhoid, 3. Jaundice, 4. Cholera

19. Nuisance growth of aquatic plants and bloom-forming algae in natural waters is generally due to high concentrations of
(a) Carbon (b) Sulphur (c) Calcium (d) Phosphorus
Answer. (d) Nuisance growth of aquatic plants and bloom-forming algae in natural waters is generally due to high concentrations of phosphorus.

20. Algal blooms impart a distinct colour to water.due to
(a) Their pigments
(b) Excretion of coloured substances
(c) Formation of coloured chemicals in water facilitated by physiological degradation of algae.
(d) Absorption of light by algal cell wall.  
Answer. (a) Algal blooms impart a distinct colour to water due to their pigments.

21. Match the items in column 1 and column II and choose the correct option:
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The correct match is:
(a) A—ii, B—i, C—iv, D—iii (b) A—iii, B—ii, C—iv, D—i
(c) A—iii, B—iv, C—i, D—ii (d) A—iii, B—i, C—iv, D—i
Answer. (c)
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22. In the textbook you came across Three Mile Island and Chernobyl disasters associated with accidental leakage of radioactive wastes. In India we had Bhopal gas tragedy. It is associated with which of the following?
(a) CO2 (b) Methyl Iso-Cyanate
(c) CFC’s (d) Methyl Cyanate
Answer. (b) In the textbook we came across Three Mile Island and Chernobyl disasters associated with accidental leakage of radioactive wastes. In India we had Bhopal gas tragedy. It is associated with Methyl Iso-Cyanate (MIC).

Very Short Answer Type Questions
1. Use of lead-free petrol or diesel is recommended to reduce the pollutants emitted by automobiles. What role does lead play?
Answer. Anti knocking agent

2. In which year was the Air (Prevention and Control of Pollution) Act amended to include noise as air pollution?
Answer. 1987.

3. Name the city in our country where the entire public road transport runs on CNG.
Answer. Delhi.

4. It is a common practice to undertake desilting of the overhead water tanks. What is the possible source of silt that gets deposited in the water tanks?
Answer. The soil particles carried by water from the source of supply.

5. What is cultural eutrophication?
Answer. Pollutants from man’s activities like effluents from the industries and homes can radically accelerate the aging process. This phenomenon has been called Cultural or Accelerated Eutrophication.

6. List any two adverse effects of particulate matter on human health.
Answer. When particulate matter inhaled deep into the lungs they cause:

  1. Breathing and respiratory symptoms
  2.  Irritation
  3.  Inflammations
  4. Damage to the lungs and premature deaths.

7. What is the raw material for polyblcnd?
Answer. Plastic waste.

8. Blends of polyblend and bitumen, when used, help to increase road life by a factor of three. What is the reason?
Answer. Blends of polyblend and bitumen, when used to lay roads, enhanced the bitumen’s water repellant properties, hence helped to increase road life by a factor of three.

9. Mention any two examples of plants used as wind breakers in the agricultural fields.
Answer. Acacia and Neem.

10. Name an industry which can cause both air and thermal pollution and as well as eutrophication.
Answer. Fertiliser factory.

11. What is an algal bloom?
Answer. Presence of large amounts of nutrients in waters causes excessive growth of planktonic (free-floating) algae, called an algal bloom.

12. What do you understand by biomagnification?
Answer. Biomagnification refers to increase in concentration of the toxicant at successive trophic levels.

13. What are the three major kinds of impurities in domestic wastewater?
Answer. 1. Suspended solids, e.g., Sand, silt and clay.
2. Colloidal materials, e.g., Fecal matter, bacteria, cloth and paper fibres.
3. Dissolved materials, e.g., Nutrients (nitrate, ammonia, phosphate, sodium, calcium).

14. What is reforestation?  
Answer. Reforestation is the process of restoring a forest that once existed but was removed at some point of time in the past.

15. What is the best solution for the treatment of electronic wastes?
Answer. Recycling.

Short Answer Type Questions
1. Is it true that carpets and curtains/drapes placed on the floor or wall surfaces can reduce noise level. Explain briefly.
Answer. Yes, carpets and curtains/drapes placed on the floor or wall surfaces can reduce noise level because these are sound absorber substances.

2. What is hybrid vehicle technology? Explain its advantages with a suitable example?
Answer. Vehicles running on dual mode like petrol and CNG are hybrid vehicle. As CNG is a green fuel there is conservation of fossil fuels and reduction in the environmental pollution.

3. Is it true that if the dissolved oxygen level drops to zero, the water will become septic? Give an example which could lower the dissolved oxygen content of an aquatic body.
Answer. Yes, the water become septic if the dissolved oxygen drops to zero. Organic pollution (biodegradable) is an example.

4. Name any one greenhouse gas and its possible source of production on a large scale. What are the harmful effects of it?
Answer. CO2 and Methane. CO2 levels are increasing due to burning of fossil fuels, leading to Global Warming.

5. It is a common practice to plant trees and shrubs near the boundary walls of buildings. What purpose do they serve?
Answer. The plants growing near the boundary wall act as barriers for sound pollution and act as dust catchers.

6. Why has the National Forest Commission of India recommended a relatively larger forest cover for hills than for plains?
Answer. The National Forest Commission of India recommended a relatively larger forest cover for hills than for plains to reduce the chances of landslides.

7. How can slash and bum agriculture become environment friendly?
Answer. Slash and bum agriculture, commonly called as Jhum cultivation in the north-eastern states of India, has also contributed to deforestation. In slash and bum agriculture, the farmers cut down the trees of the forest and bum the plant remains. The ash is used as a fertilizer and the land is then used for farming or cattle grazing. After cultivation, the area is left for several years so as to allow its recovery. The farmers then move on to other areas and repeat this process. In earlier days, when Jhum cultivation was in prevalence, enough time-gap was given such that the land recovered from the effect of cultivation. With increasing population, and Treated cultivation, this recovery phase is done away with, resulting in deforestation.

8. What is the main idea behind “Joint Foregt Management Concept”introduced by the Government of India?
Answer. Realising the significance of participation by local communities, the Government of India in 1980s has introduced the concept of Joint Forest Management (JFM) so as to work closely with “the local communities for protecting and managing forests. In return for their services to the forest, the communities get benefit of various forest products (e.g., fruits, gum, rubber, medicine, etc.), and thus the forest can be conserved in a sustainable manner.

9. What do you understand by Snow-blindness?
Answer. In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of cornea, called snow-blindness.

10. How has DDT caused decline in bird population?
Answer. High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations.

11. Observe the figure A and B given below and answer the following questions
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(i) The power generation by the above two methods is non-polluting. True/False
(ii) List any two applications of solar energy.
(iii) What is a photovoltaic cell?
Answer. (i) True.
(ii) (a) Electricity generation (b) Solar light
(iii) A photovoltaic cell is a semiconductor diode that converts visible light into direct current (DC).

Long Answer Type Questions
1. Write a short note on electronic waste. List the various sources of e-wastes and the problems associated with its disposal.
Answer. Discarded unusable electronic gadgets such as computers, mobile phones, circuits, television sets, etc., form electronic waste. These contain harmful toxic substances like heavy metals to which the unskilled manual workers are directly exposed.

2. What is organic farming? Discuss the benefits of organic fanning as a viable practise in the context of developing nations like India.
Answer. The use of Biofertilisers in agriculture is called organic farming. Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria. The nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient. Other bacteria can fix atmospheric nitrogen while free- living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.
Currently, in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers.

3. Water logging and soil salinity are some of the problems that have come in the wake of the Green Revolution. Discuss their causes and adverse effects to the environment.
Answer. Water logging and soil salinity are some of the problems that have come in the wake of the Green Revolution. Irrigation without proper drainage of water leads to water logging in the soil. Besides affecting the crops, water logging draws salt to the surface of the soil. The salt then is deposited as a thin crust on the land surface or starts collecting at the roots of the plants. This increased salt content is inimical to the growth of crops and is extremely damaging to agriculture.

4. What are multipurpose trees? Give the botanical and local names of any two multipurpose trees known to you and list their uses.
Answer. Multipurpose trees are that which are grown for more than one purpose or benefits. They may provide food in the form of fruit, seeds, or roots; and also provides firewood, medicines, fibres, etc.
(i) Neem (Azadirachta indicd)— Used as insect repellent, antibiotic, firewood and windbreaks.
(ii) Coconut palm (Cocos nucifera)— Used for food, purified water (juice from inside the coconut), roof thatching, firewood, shade and rope making.

5. What are the basic characteristics of a modem landfillsite. List any three and also mention the reasons for their use.
Answer. Characteristics of a modem landfill include:

  1. Methods to contain leachate such as lining clay or plastic liners.
  2. Compaction and covering of the waste to prevent it from being blown by wind.
  3. Installation of a landfill gas extraction system to extract the gas for use in generation of power.

6. How does an electrostatic precipitator work?
Answer. Electrostatic precipitator has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons. These electrons attach to dust particles giving them a net negative charge. The collecting plates are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust to fall.
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7. Observe figure and answer the followiag,questions.
(i) What ecological term is used to describe the DDT accumulation at different trophic levels?
(ii) list any one effect of DDT accumulation on birds.
(iii) Will DDT accumulation lead to eutrophication?
Does it affect the BOD?
Name disease caused by accumulation of any heavy metal.
Answer. (i) Biomagnification
(ii) High concentrations of DDT disturb, calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations.
(iii) Yes.
(iv) Yes, it increases the BOD.
(v) Disease caused by eating fish found in water contaminated with industrial waste having mercury is Minamata disease. Cd pollution associated with disease is called “Itai-Itai”. Arsenic (As) poisoning causes “Black foot disease”.
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