CBSE Class 12 Biology Environmental Issues Worksheet Set B

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

2. Name the city in our country where the entire public road transport runs on CNG.

3. What is cultural eutrophication?

4. What is the raw material for polyblend?

5. What is an algal bloom?

6. What is the best solution for the treatment of electronic wastes?

7. What is the main idea behind “Joint Forest Management Concept” introduced by the Government of India?

8. What do you understand by Snow-blindness?

9. DDT content in the water of a lake that supplies drinking water to the near by villages, is found to be 0.003ppm.The kingfishers of that area are reported to have 2ppm of DDT. Why has the concentration increased in these birds? What harm will this cause to the bird population? Name the phenomenon.

10. Thermal power plants are inevitable in an industrial and densely populated country like ours. What harm do they do to the environment? Also mention any precaution that could be taken to save our environment.

Important Questions for NCERT Class 12 Biology Environmental Issues

Question. The Bharat Stage-III, norms for reducing the level of vehicular pollutant, is equivalent to -
(a) Euro-I norms
(b) Euro-II norms
(c) Euro-III norms
(d) Euro-IV norms

Answer : C

Question. Pollution is undesirable changes in physical, chemical and biological properties. Which among the following is not air pollution induced plant injury -
(a) Reduced growth and yield
(b) Premature death of plant
(c) Clogging of Stomata
(d) Oxygen binding ability

 Answer : D

Question. Air (Prevention and control of pollution) act 1981 was amended in 1987 to include __________ as an air pollutant. -
(a) Particulated matter
(b) Hydrocarbons
(c) Noise
(d) Radioactive pollutants

Answer : C

Question. The ozone hole over Antarctica develops each year between -
(a) Late August and early October
(b) Early August and late October
(c) Early October and early December
(d) Late October and late December 

Answer : A

Question. Which of the following is not a result of water logging-
(a) Deposition of salt crust on land
(b) Collection of salts around root
(c) Damage to agriculture
(d) Leaching of salts

Answer : D

Question. The Specific intensity of noise, which may damage ear drums and causes permanently impairing hearing ability is -
(a) Equal and less than 150 dB
(b) Equal and more than 150 dB
(c) Less than 20 dB
(d) Less than 80 dB

Answer : B

Question. Noise as one of the important air pollutant is not responsible for -
(a) Sleeplessness
(b) Increase heart beating
(c) Altered breathing pattern
(d) Decreased oxygen carrying capacity

Answer : D

Question. To safe guard our water resources, water (prevention and control of pollution) act was came in force -
(a) 1971
(b) 1972
(c) 1974
(d) 1981

Answer : C

Question. According to National forest policy (1988) of India has recommended 33% forest cover for plains and_______% area for hills.-
(a) 30%
(b) 19.4%
(c) 67%
(d) 76%

Answer : C

Question. Montreal Protocol was come in action from -
(a) 1987
(b) 1988
(c) 1989
(d) 1992

Answer : C

Question. Which among the following is not a result of Deforestration -
(a) Enhanced carbondioxide concentration
(b) loss of biodiversity
(c) Ozone depletion
(d) Disturbed hydrological cycle

Answer : C

Question. According to Euro-III norms, which among the following standard is not true -
(a) Sulphur should be controlled at 350 ppm in Diesel 
(b) Sulphur should be controlled at 150 ppm in petrol
(c) Aromatic hydrocarbons should be contained at 42 percent
(d) Sulphur content should be controlled at 50 ppm in petrol and diesel

Answer : D

Ques. The maximum biomagnification would be in which of the following in case of aquatic ecosystem?
(a) Zooplanktons
(b) Phytoplanktons
(c) Fishes
(d) Birds 

Answer: D

Ques. Which one of the following organisms is used as indicator of water quality?
(a) Azospirillum
 (b) Escherichia
(c) Biggiata
(d) Chlorella 

Answer: B

Ques. The most common indicator organism that represents polluted water is
(a) C.vibrio
(b) Entamoeba histolytica
(c) E.coli
(d) P.typhi. 

Answer: C

Ques. Phosphate pollution is caused by
(a) sewage and phosphate rock
(b) sewage and agricultural fertilizers
(c) phosphate rock only
(d) agricultural fertilizers only. 

Answer: B

Ques. When huge amount of sewage is dumped into a river, its B.O.D. will
(a) slightly decrease
(b) remain unchanged
(c) increase
(d) decrease. 

Answer: C

Ques. In Minamata Bay Japan the animals which remained free from minamata disease, are
(a) dogs
(b) cats
(c) pigs
(d) rabbits. 

Answer: D

Ques. A dental disease characterized by mottling of teeth is due to the presence of certain chemical element in drinking water. Which of the following is that element?
(a) Fluorine
(b) Boron
(c) Mercury
(d) Chlorine

Answer: A

Ques. Which among the following is likely to have the highest levels of D.D.T. depositions in its body?
(a) Sea gull
(b) Phytoplankton
(c) Eel
(d) Crab 

Answer: A

Ques. A disease caused by eating fish contaminated by industrial waste, containing mercury compounds, is called
(a) osteosclerosis
(b) Hashimoto’s oxidase
(c) Bright’s disease
(d) Minimata disease.

Answer: D

Ques. American water plant that has become a troublesome water weed in India is
(a) Cyperus rotundus
(b) Eichhornia crassipes
(c) Typha latifolia
(d) Trapa bispinosa.

Answer: B

Ques. Polyblend, a fine powder of recycled modified plastic, has proved to be a good material for
(a) making tubes and pipes
(b) making plastic sacks
(c) use as a fertiliser
(d) construction of roads. 

Answer: D

Ques. Which of the following methods is the most suitable for disposal of nuclear waste?
(a) Bury the waste within rocks deep below earth’s surface
(b) Shoot the waste into space
(c) Bury the waste under Antarctic ice-cover
(d) Dump the waste within rocks under ocean

Answer: A

Ques. Which one of the following statements is incorrect in case of Bhopal tragedy?
(a) Methyl isocyanate gas leakage took place.
(b) Thousands of human beings died.
(c) Radioactive fall out engulfed Bhopal.
(d) It took place in the night of December 2/3, 1984.

Answer: C

Ques. In 1984, the Bhopal gas tragedy took place because methyl isocyanate
(a) reacted with DDT
(b) reacted with ammonia
(c) reacted with CO₂
(d) reacted with water. 

Answer: D

Ques. In 1984, Bhopal gas tragedy was caused due to leakage of
(a) potassium isocyanate
(b) methyl isocyanate
(c) sodium monoxide
(d) none of these.

Answer: B

Ques. The two great industrial tragedies namely, MIC and Chernobyl tragedies respectively occurred where and at which time?
(a) Bhopal 1984, Ukraine 1986
(b) Bhopal 1986, Russia 1988
(c) Bhopal 1984, Ukraine 1990
(d) Bhopal 1984, Ukraine 1988 

Answer: A

Ques. Which of the following isotopes is most dangerous to Homo sapiens?
(a) Phosphorus-32
(b) Strontium-90
(c) Cesium-137
(d) Iodine-131

Answer: B

Ques. Gas released during Bhopal tragedy was
(a) methyl isocyanate
(b) potassium isothiocyanate
(c) sodium isothiocyanate
(d) ethyl isothiocyante. 

Answer: A

Ques. Which of the following pairs of gases is mainly responsible for greenhouse effect?
(a) Carbon dioxide and methane
(b) Ozone and ammonia
(c) Oxygen and nitrogen
(d) Nitrogen and sulphur dioxide 

Answer: A

Ques. The UN Conference of Parties on climate change in the year 2012 was held at
(a) Lima
(b) Warsaw
(c) Durban
(d) Doha. 

Answer: D

Ques. The UN Conference of Parties on climate change in the year 2011 was held in
(a) Peru
(b) Qatar
(c) Poland
(d) South Africa.

Answer: D

Very Short Answer Questions

Question. Mention the information that the health workers derive by measuring BOD of a water body.
Answer: By measuring BOD of a water body, health workers find the amount of dissolved oxygen in water. The lesser the amount of dissolved oxygen, the more polluted the water body will be.

Question. Why is the use of unleaded petrol recommended for motor vehicles equipped with catalytic converters? 
OR
Why is it desirable to use unleaded petrol in vehicles fitted with catalytic converters?
Answer : Lead in petrol inactivates the catalysts (platinum, palladium and rhodium) which convert harmful pollutants (CO, unburnt hydrocarbons, nitric oxide) to lesser harmful pollutants (CO₂, H₂O, N₂).

Question. Why are lichens regarded as pollution indicators?
Answer : Lichens are regarded as pollution indicators because they do not grow in areas that are polluted.
So their presence indicates no pollution in that area and their absence indicates that the area is polluted.

Question. Which of the following is not a greenhouse gas?
CO₂, CH₄, O₂, CFCs.
Answer : O₂.

Question. Why does ozone hole form in spring and not in winter?
Answer : Sunlight is necessary for ozone degradation and it is available only during spring.

Question. Excessive nutrients in a fresh water body cause fish mortality. Give two reasons.
Answer: Excessive nutrients result in excessive algal growth or eutrophication in the water body. Thus, the water quality becomes poor as the oxygen level decreases.

Question. How is snow-blindness caused in humans? 
Answer. In human eye, cornea absorbs UV-B radiation, and a high dose of UV–B causes inflammation of cornea leading to snow-blindness.

Question. Why is Eichhornia crassipes nicknamed as “Terror of Bengal”? 
Answer: Eichhornia crassipes is an aquatic weed that grows abundantly and very fast in eutrophic water bodies and causes imbalances in water ecosystem. It causes oxygen depletion leading to death of aquatic life (eutrophication).

Question. Name two greenhouse gases produced by anaerobic microbes. 
Answer: Carbon dioxide and methane.

Question. In which year was the Air Prevention and control of pollution Act amended to include noise as air pollution.
Answer: 1987.

Question. State the cause of accelerated eutrophication. 
Answer: Pollutants from human activities, effluents from industries, effluents from home, sewage and agricultural wastes (chemical wastes) radically accelerate the aging process.

Short Answer Questions

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

Question. A crane had DDT level at 5 ppm in its body. What would happen to the population of such birds? Explain giving reasons.
OR
DDT content in the water of a lake that supplies drinking water to the nearby villages, is found to be 0.003 ppm. The kingfishers of that area were reported to have 2 ppm of DDT. Why has the concentration increased in these birds? What harm will this cause to the bird population?
Name the phenomenon.
Answer. DDT being a toxic substance gets accumulated in the organism and passes on to the next higher trophic level because it cannot be metabolised or excreted. Thus, concentration of DDT has increased in the birds in the given case. The high concentration of DDT disturbs the calcium metabolism in birds, causes thinning of eggshells, their premature breaking and eventually causes a decline in the bird population.The phenomenon is called biomagnification.

Question. Ornithologists observed decline in the bird population in an area near a lake after the setting of an industrial unit in the same area. Explain the cause responsible for the decline observed.
Answer. Harmful wastes from the industrial unit must have entered the trophic levels of food chain causing biomagnification. It must have accumulated in the birds as it can neither be metabolised nor be excreted. High concentration of harmful chemical may disturb calcium metabolism in birds causing thinning of the egg shells and their premature breaking, ultimately causing decline in bird populations.

Question. Study the graph given below. Explain how is oxygen concentration affected in the river when sewage is discharged into it.

Answer. When sewage is discharged into the river, the oxygen concentration declines sharply because a large amount of oxygen is consumed by aerobic microorganisms in river to decompose the organic matter in river. When the amount of organic matter reduces, the amount of dissolved oxygen again increases.

Question. How do automobiles fitted with catalytic converters reduce air pollution? Suggest the best fuel for such vehicles.
Answer. Catalytic converters have expensive metals like platinum-palladium and rhodium as catalysts.
As exhaust emission passes through 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.Unleaded petrol is the best fuel for such vehicles.

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

Question. Chlorofluorocarbons (CFCs) are widely used as refrigerants. Then why is it suggested to reduce its emission as far as possible? Explain. 
OR
Refrigerants are considered to be a necessity in modern living, but are said to be responsible for ozone holes detected in Antarctica. Justify.
Answer. CFCs find wide use as refrigerants. CFCs discharged in the lower part of atmosphere move upward and reach stratosphere. In stratosphere, UV rays act on them releasing chloride atoms. Chloride atoms degrade ozone, releasing molecular oxygen. Whatever CFCs are added to the stratosphere have permanent and continuing effects on ozone. These have resulted in ozone hole.

Question. Why are there regular reminders to reduce the use of CFCs in the production of industrial and household appliances? Explain. 
Answer. CFCs discharged in the lower part of atmosphere move upward and reach stratosphere. In stratosphere, UV rays act on them releasing Cl atoms, which in turn degrade ozone. Ozone depletion will result in entry of harmful UV-B radiations into the earth’s atmosphere resulting in deleterious effects on all living organisms.

Question. Plenty of algal bloom is observed in a pond in your locality.
(a) Write what has caused this bloom and how does it affect the quality of water.
(b) Suggest a preventive measure.
Answer. (a) Presence of large amounts of nutrients (Nitrogen and Phosphorus) in water causes excessive growth of algae. This growth depletes dissolved oxygen in water and imparts distinct colour to the water bodies. The bloom forming algae are extremely toxic and deteriorates water quality resulting in fish mortality.
(b) Following preventive measures can be carried out:
(i) Treatment of waste water before it reaches the pond.
(ii) Integrated waste water treatment.
(iii) Avoid using NPK fertilisers.
(iv) Use of organic or biodegradable manure or resort to organic farming.

Question. Explain giving reasons the cause of appearance of peaks ‘a’ and ‘b’ in the graph shown below.

Answer. ‘a’–High BOD due to sewage discharge.
‘b’–Increase in dissolved oxygen due to sewage decomposition. Micro-organisms involved in biodegradation of organic matter consume a lot of oxygen, therefore,there is a sharp decline in dissolved oxygen. When the sewage is completely degraded, oxygen concentration again increases.

Question. (a) Rearrange the following greenhouse gases in increasing order of their relative contribution to the total global warming:
N₂O; CFC; CO₂; C₂H₄
(b) What is the effect of global warming on polar ice-caps? Comment on its possible ecological impact. 
Answer. (a) C₂H₄ < N₂O < CFC < CO₂
(b) Global warming results in rise of atmospheric temperature. This leads to the increased melting of polar ice caps which will cause the rise in sea level and many coastal areas will be submerged.

Question. Justify the need for signing of Montreal Protocol by the participating nations.
Answer. The Montreal Protocol was signed to control the emission of ozone depleting substances. Excessive use of CFCs and other ozone depleting chemicals has resulted in thinning of ozone layer. Further thinning would allow harmful UV-B radiations to enter Earth’s atmosphere and have deleterious effects on living organisms.

Question. It is a common practice to plant tree and shrubs near the boundary walls of building. What purpose do they serve?
Answer. The plant growing near the boundary wall act as barrier for sound pollution and act as dust catchers.

Question. What is ozone shield and why is it important? Name the gases that cause stratospheric ozone depletion.
Answer. The thin layer of ozone around the atmosphere that prevents entry of harmful UV rays is called ozone shield. Ozone shield functions as a shield against strong UV radiations. The gases that cause ozone depletion are methane, nitrous oxide and chlorofluorocarbons.

Question. What is polyblend? Why did the plastic manufacturers think of producing it? Write its usefulness. 
Answer. Polyblend is a fine powder of recycled modified plastic. Polyblend was produced to recycle plastic waste. When blended with bitumen, polyblend can be used to lay roads that have increased road life.

Question. Mention how e-waste is produced and disposed off. Write the solution for its treatment.
OR 
Name any two sources of e-wastes and write two different ways for their disposal.
OR 
How e-wastes are being handled in our country? Write the correct solution for treating this waste. 
Answer. Irreparable computers and other electronic goods are the known sources of electronic wastes (e-wastes). E-wastes are buried in landfills or incinerated. Recycling is the only solution for the treatment of e-wastes.

Question. With the help of a flow chart, show the phenomenon of biomagnification of DDT in an aquatic food chain. 
Answer. 

Question. Write what was the percentage of forest cover of India at the beginning and at the end of the twentieth century. How different is it from the one recommended by the National Forest Policy of our country?
Answer. At the beginning of the twentieth century, forests covered about 30 % of the land of India. By the end of the century, it shrunk to 19.4 %, whereas the National Forest Policy (1988) of India has recommended 33 % forest cover for the plains and 67 % for the hills.

Question. Justify the need for signing of ‘Montreal Protocol’ by the participating nations in 1987.
Answer. Montreal Protocol has been signed to control the emission of ozone depleting substances which results in thinning of ozone layer and allows the UV rays to penetrate the earths surface. These harmful UV rays cause deleterious effects (cataract/skin cancer/ageing of skin.)