CBSE Class 12 Biology HOTs Environmental Issues

Very Short Answer Questions

Question. Mention two advantages for preferring CNG over diesel as an automobile fuel. 
Answer. Advantages of CNG are:
(i) burns efficiently and leaves behind less unburnt residues
(ii) cheaper than petrol or diesel
(iii) causes less pollution
(iv) cannot be adulterated
(v) cannot be siphoned by thieves. (any two)

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

Question. 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.

Question. Name the city in which the entire public road transport runs on CNG. 
Answer. Delhi.

Question. List two advantages of the use of unleaded petrol in automobiles as fuel.
Answer. (i) Allows the catalytic convertor to remain active.
(ii) Reduces air pollution.

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. An electrostatic precipitator in a thermal power plant is not able to generate high voltage of several thousands. Write the ecological implication because of it. 
Answer. As a result of this particulate matter or dust particles will be released in the air causing air pollution.

Question. What is an algal bloom? 
Answer. The excessive growth of algae (free-floating) that causes colouration of water bodies is called algal bloom.

Short Answer Questions

Question. 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.
Answer. The particulate and gaseous pollutants are released from thermal power plants which lead to harmful effects. These pollutants can cause:
(i) breathing or respiratory symptoms when inhaled.
(ii) irritation, inflammations and damage to lungs and premature death.
Precautionary measures include use of electrostatic precipitators by which 99% of the particulate matters can be removed from the exhaust.

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. A person has inhaled air having particulate pollutants of size less than 2.5 micrometers in diameter. What could be the impact of their pollutants on his respiratory system? 
Answer. Particulate pollutants inhaled deep into the lungs cause irritation, inflammation, damage to the lungs, and premature death.

Question. (a) Name any two places where it is essential to install electrostatic precipitators. Why it is required to do so?
(b) Mention one limitation of the electrostatic precipitator. 
Answer. (a) It is essential to install electrostatic precipitators in thermal power plants and smelters to remove particulate matter.
(b) Limitation of the electrostatic precipitator:
(i) particulate matter less than 2.5 micrometres are not removed.
(ii) velocity of air between plates must be low enough to allow the dust to fall.
(iii) it cannot work without electricity. (Any one)

Question. Discuss the role of women and communities in protection and conservation of forests.
Answer. Women and communities played an important role in protection and conservation of forests. In 1731, a Bishnoi woman, Amrita Devi showed exemplary courage by hugging a tree to prevent its cutting. Amrita Devi Bishnoi Wildlife protection Award is being awarded by the Government of India to individuals or communities from rural areas that show extraordinary courage and dedication in protecting wildlife. In Garhwal, local women hugged trees to prevent the contractor from cutting down trees.

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. Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
Answer. (i) Cause
• Increase in the level of greenhouse gases (CO2, methane, etc.) in the atmosphere.
These gases allow the heat waves to reach earth but prevent their escape and thus the earth becomes warm.
(ii) Effects
• The temperature of the earth has increased by 0.6°C in the last three decades, which will lead to changes in precipitation patterns.
• Rise in temperature leads to deleterious changes in environment resulting in odd climatic changes called El Nino effect.

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. (a) Why are the colourful polystyrene and plastic packaging used for protecting the food,considered an environmental menace?
(b) Write about the remedy found for the efficient use of plastic waste by Ahmed Khan of Bangalore. 
Answer. (a) The colourful polystyrene and plastic packaging are non-biodegradable and non-ecofriendly.
(b) The remedy was found by developing polyblend, which is a fine powder of recycled modified plastic. Polyblend is mixed with bitumen to lay roads. This enhanced the water repellent
property of bitumen and enhanced the life of roads.

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.

Long Answer Questions

Question. Explain any three remedial measures to overcome the acute air pollution in our cities.
Answer. (i) Electrostatic precipitators to remove paritculate matter present in the exhaust from thermal power plant.
(ii) Scrubber to remove SO2 from the exhaust of thermal power plant.
(iii) Alternative sources of energy in place of petrol.
(iv) Lead-free petrol or diesel.
(v) Catalytic convertors – to reduce lead pollution.
(vi) Use of CNG.
(vii) Use of low sulphur petrol and diesel.
(viii) Phasing out of old vehicles and stringent enforcement of pollution level norms.

Question. (i) State the consequence if the electrostatic precipitator of a thermal plant fails to function.
(ii) Mention any four methods by which the vehicular air pollution can be controlled.
Answer. (i) Particulate matter will pollute the air.
(ii) Vehicular pollution can be controlled by:
Control of air pollution in Delhi
• In 1990’s Delhi ranked 4th among 41 most polluted cities of the world. A Public Interest Litigation (PIL) was filed in the Supreme Court.
• All buses of Delhi were converted to run on CNG by the end of 2002 as per the directives of the Supreme Court.
• Advantages of CNG over diesel/petrol:
(a) CNG burns most efficiently without leaving any unburnt remnant behind.
(b) CNG is cheaper than petrol or diesel.
(c) CNG cannot be siphoned off by thieves and adulterated like petrol or diesel.

Question. How does an electrostatic precipitator work to remove particulate pollutants released from the thermal power plants? 
Answer. Electrostatic precipitator (ESP)
• It is an electrical device used to remove particulate matter present in the exhaust of thermal power plant.
• More than 99% particulate matter can be removed by this method.
• ESP has electrode wires and a stage of collecting plates.
• Electrode wires are provided with an electric current of several thousand volts, which produces a corona that releases electrons.
For diagram,

Question. Mention the major cause of air pollution in metro cities. Write any three ways by which it can be reduced. 
Answer. Major causes of air pollution are: Causes
(a) Smoke from forest fires, volcanic eruptions, etc.
(b) Decomposition of garbage resulting in release of unwanted gases into the atmosphere.
(c) Burning of fossil fuels in automobiles and industries release particulate and air pollutants.
(d) Use of leaded petrol.
(e) Gaseous wastes or particulate matter as by-products of various industries.
(f) Smoke stacks of thermal power plants, smelters and other industrial release, particulate and gaseous air pollutants with harmless gases like N2, O2, etc.
Control methods:
(i) Using electrostatic precipitators to remove particulate matter from exhaust of industries and thermal power plant.
(ii) Using scrubber to remove gases like SO2.
(iii) Use of catalytic converters in automobiles for reducing emission of poisonous gases.

Question. By the end of 2002 the public transport of Delhi switched over to a new fuel. Name the fuel.
Why is this fuel considered better? Explain.
Answer. The fuel was CNG or compressed natural gas. CNG is considered better because of the following reasons:
(i) CNG burns more efficiently unlike diesel or petrol.
(ii) Very little of it is left unburnt.
(iii) It cannot be adulterated.
(iv) It is cheaper than petrol or diesel.

Question. Discuss briefly the following:
(a) Radioactive wastes
(b) Defunct ships and e-wastes
(c) Municipal solid wastes
Answer. (a) Radioactive wastes: These are nuclear wastes which are most potent pollutants as they cause mutations. These cannot be reused or recycled and are disposed off carefully to prevent leakage.
(i) Accidents: There are accidental leakage as in Three Mile Island and Chernobyl incidents.
(ii) Radioactive waste disposal: Radiation given off by nuclear waste is extremely damaging to living organisms as it causes mutation at an extremely high rate, causing cancer.
Therefore, nuclear waste is an extremely potent pollutant.
(b) Defunct ships: Old defunct ships are dismantled to obtain scrap metals. Defunct ships contains toxicants like asbestos, mercury, lead, tributylin, etc. The workers engaged in ship are exposed to toxic chemicals. The coastal areas connected with ship breaking yard also become polluted.
e-wastes: These are the wastes (like irreparable computers and other electronic goods) generated in the developed countries and exported to developing countries including India, China and Pakistan where metals like gold, nickel, silicon, copper, iron, etc., are recovered during recycling process. Recycling is done manually by workers and hence they are exposed to some toxic substances.
(c) Municipal solid wastes: Wastes produced from homes, offices, schools, hospitals, etc., are collected and disposed off by the municipality. These generally consists of paper, leather,
textile, rubber, glass, etc. Sanitary landfills are used to dump these wastes.

Question. Write any three ways by which noise pollution affects the human body adversely. List any three steps that should be followed in order to reduce noise pollution. 
Answer. Effects of noise pollution are: sleeplessness, increased heart beat, altered breathing pattern,damaged hearing ability and damaged ear drum (Any three)
Steps to be followed to reduce noise pollution:
(i) Following of stringent laws laid down in relation to noise level.
(ii) Delimitation of horn free zones around hospitals and schools.
(iii) To adopt permissible sound level of crackers and loudspeakers.
(iv) Adhereing to time limit for loudspeakers beyond which it cannot be played.
(v) Use of sound absorbent material in industries.
(vi) Muffling of noise. (Any three)

ONE MARK QUESTIONS:

3. Name four metals which are recovered during the recycling of e-waste?

 

Ans: Copper, Iron Silicon Nickel and Gold.

 

4. Complete the following:

             A                                                   B

1. ____________                Carbon monoxide & Nitrogen oxide

2. Electrostatic precipitator            ______________________

3. _____________                              High noise level

4. Land fills                                    _____________________

 

Ans: 1. Catalytic converter

2. Particulate matter

3. Earmuffs

4. Solid waste

 

5. Water  →  Zooplanktons   →   Small fish    →   Fish eating birds

DDT (0.003ppm) (0.04ppm)        (0.5ppm)              (5ppm)

Why is the concentration of DDT increasing from the producers to consumers in the above food chain?

 

THREE MARKS QUESTIONS:

 

1. Why is CNG preferred than petrol or diesel?

Hint: Fuel efficiency, no adulteration, no theft

 

2. What are the wastes generated during trips and tours? How can it be minimized?

 

3. How do foam and ecosan help in waste water treatment?

 

FIVE MARKS QUESTIONS:

 

1. What measures would you take to reduce environmental pollution?

Hint: no biomass burning, vehicle use, no tobacco, electric chimney, noise, tree plantation, disposable and recyclable material, minimize fossil fuels.

 

2. Observe the following diagram and answer the questions at the end 

a. Name the gases.(2)
b. Comment on the consequences of increase in the level of each gas (any three)(3)