Environmental Issues Questions Class 12 Biology

ICSE Class 12 Biology

Pollution, Solid and Radioactive Wastes

Very Short Answer Type Questions

Question. List two advantages of the use of unleaded petrol in automobiles as fuel.
Answer : The advantages are as follows :
(i) Unleaded petrol does not release lead compounds from exhaust fumes into the atmosphere and causes less pollution.
(ii) It does not emit harmful compounds, it helps in preventing health diseases like bronchitis, asthma and lung diseases.
(iii) It allows catalytic converter to remain active.

Question. Why should motor vehicles equipped with catalytic convertors use unleaded petrol ?
Why is it desirable to use unleaded petrol in vehicles fitted with catalytic converters ? 
Answer : Lead in petrol inactivates the catalysts and harmful pollutants (CO, unburnt hydrocarbons, nitric oxide) are converted to lesser harmful pollutants (CO2, H2O, N2

Question. Write the name of organism which is referred to as
‘‘Terror of Bengal’’.
Answer : Water hyacinth (Eichhornia crassipes). 

Question. Excessive nutrients in a fresh water body cause fish mortality. Give two reasons.
Answer : Excessive nutrients in a freshwater body cause fish mortality due to the following reasons :
(i) Depletion of dissolved oxygen.
(ii) Increase in toxic material in water body.

Question. Inspite of being non-polluting why are there great apprehensions in using nuclear energy for generating electricity ?
Answer : Accidental leakages, safe disposal of radioactive waste. 

Question. BOD of two samples of water A & B were 120 mg/l and 400 mg/L respectively. Which sample is more polluted ?
Answer : Sample B is more polluted than Sample A.

Question. List two gaseous products that are produced when exhaust of an automobile passes through a catalytic converter.
Answer : Carbon monoxide and nitric oxide. (When an automobiles exhaust passes through catalytic converter, it converts nitric oxide into nitrogen and oxygen and carbon monoxide to CO2 and unburnt hydrocarbons get completely burnt into CO2 and H2O.)

Question. How do algal blooms affect the life in water bodies ?
Answer : Algal bloom causes deterioration of the water quality and aquatic life mortality.

Question. State the cause of Accelerated Eutrophication.
Answer : Pollutants from human activities / effluents from industries / effluents from home / sewage / agricultural (chemical) wastes radically accelerate the ageing process. 

Short Answer Type Questions – l

Question. How e-wastes are being handled in our country? Write the correct solution for treating this waste.
Answer : E-wastes are being buried in landfills, or incinerated (manually). Recycling this waste in the environment friendly manner is the right solution. 

Question. What is polyblend ? Why did the plastic manufacturers think of producing it ? Write its usefulness.
Answer : Polyblend : It is a fine powder of recycled modified plastic developed by a Bangalore-based company. This mixture is mixed with the bitumen that is used to lay roads.
The plastic sack manufacturer in Bangalore has managed to find the ideal solution to the everincreasing problem of accumulating plastic waste.
Polyblend and bitumen, when used to lay roads, enhanced the bitumen—water repellant properties and helped to increase the road life by a factor of three.

Question. Name any two sources of e-wastes and write two different ways for their disposal.
Answer : Two sources of e-wastes are : televisions and computers.
They can be disposed by :
(i) Land filling : Soil is excavated from the trenches and waste material is buried in it, which is covered by a thick layer of soil.
(ii) Recycling : Recycling is the practice of reusing items that would otherwise be discarded as waste. 

Question. Lower BOD of a water body helps reappearance of clean-water organisms. Explain.
Answer : Lowering of Biological Oxygen Demand (BOD) results in decreased biodegradable material in the water body → As result of which there is reduced microbial decomposition → when there is no decomposition, oxygen utilisation is reduced → More Dissolved Oxygen (DO) is available → clean water-organisms reappear.

Question. Study the graph given below. Explain how is oxygen concentration affected in the river when sewage is discharged into it.
Explain giving reasons the cause of appearance of peaks ‘a’ and ‘b’ in the graph shown below.

Answer : Figure indicates effect of sewage discharge on river water.
(i) (a) Represents high BOD due to sewage discharge complete.
(ii) (b) Represent increase in dissolved oxygen to sewage decomposition.
When sewage is discharged into river, microorganisms present in water helps in biodegradation of organic matter. They consume lot of oxygen. Therefore, there is sharp decline in dissolved oxygen. When the sewage is completely degraded, oxygen concentration again increases.

Question. How did Ahmed Khan, plastic sacks manufacturer from Bangalore, solve the ever-increasing problem of accumulating plastic waste ?
Answer : Collected plastic wastes-recycled-powdered-to form polyblend, blended with bitumen, used in road laying, increased road life by a factor of three / more durable.

Question. How do automobiles fitted with catalytic converters reduce air pollution? Suggest the best fuel for such vehicles.
State the function of a catalytic converter in an automobile. 
Answer : (a) Catalytic converters have expensive metals like platinum–palladium and rhodium as catalysts.
(b) As the exhaust emission passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water.
(c) Carbon monoxide and nitric oxides are changed to carbon dioxide and nitrogen gas respectively.
(d) Unleaded petrol is the best fuel.

Question. Mention the major causes of air pollution in metro cities. Write any three ways by which it can be reduced.
Answer : The major causes of air pollution in metro cities are :
(i) Smokestacks of thermal power plants, smelters and other industries.
(ii) Burning fossil fuels in automobiles, industries and households.
(iii) Smoke from forest fires, volcanic eruptions.
(iv) Decomposition of garbage, resulting in release of unwanted gases into the atmosphere. 
Three ways to reduce the air pollution are as follows :
(a) Electrostatic precipitator.
(b) Scrubber. 
(c) Catalytic converter 

Question. Mention how e-waste is produced and disposed off. Write the solution for its treatment.
Answer : Irreparable computers and other electronic goods are known as electronic wastes (e-wastes). E-wastes are buried in landfills or incinerated.
The e-wastes generated in the developed world are exported to developing countries, mainly to China, India, and Pakistan, where metals like copper, iron, silicon, nickel and gold are recovered during the recycling process. Unlike developed countries, recycling of e-wastes, in developing countries often, involves manual participation, thus exposing workers to toxic substances present in e-wastes.
Recycling is the only solution for the treatment of e-waste, provided it is carried out in an environment friendly way.

Question. Plenty of algal bloom is observed in a pond in your locality.
(i) Write what has caused this bloom and how it affect the quality of water. 
(ii) Suggest a preventive measure.
Answer : (i) Presence of large amounts of nutrients / nitrogen / phosphorus in water causes excessive growth of algae, depletes dissolved oxygen / imparts a distinct colour to the water bodies / bloom forming algae are extremely toxic / deteriorates water quality / fish mortality 
(ii) Treatment of waste water before it reaches the pond / Integrated waste water treatment / avoiding using NPK fertilizers / use of organic or biodegradable manure / resort to organic farming

Question. Explain accelerated eutrophication. Mention any two consequences of this phenomenon.
Answer : Accelerated eutrophication occurs due to the passage of sewage and run-off from fertilized fields into ponds, lakes and other water bodies. Nutrients present in sewage and fertilizers causes dense growth of plants and planktonic algae. 
Consequences of accelerated eutrophication :
(i) Eutrophic water bodies support excessive growth of floating plants, e.g., water hyacinth is one such plant that sometimes chokes ponds, lakes and rivers.
(ii) Due to increase of algal blooms, there is drastic decrease in oxygen replenishment inside water that kills aquatic animals. 

Question. How did a citizen group called Friends of Arcata Marsh, California, USA, help to improve water quality of the marshland using Integrated Waste Water Treatment? Explain in four steps.
Answer : (a) Water is treated by conventional method // sedimentation / filtration / chlorination.
(b) Water flows to six connected marshes.
(c) The water in marshes is seeded with appropriate plants / algae / fungi / bacteria.
(d) Which helps to neutralize the pollutants / assimilate the pollutants / absorb pollutants / Remove heavy metals. 

Question. Why is Eichhornia crassipes nicknamed as ‘‘Terror
Answer : Eichhornia crassipes is nicknamed as ‘Terror of Bengal’ because it grows luxuriantly in eutrophic water bodies. Its excessive growth causes blockage in our water ways, thereby leading to an imbalance in the ecosystem dynamics of water body. Its rate of excessive growth is higher than the rate of its removal. ‘‘Terror of Bengal’’ is the title given to this aquatic weed because initially it was introduced in water bodies of Bengal for its flowers and shape of leaves but however it turned out to be highly invasive water weed that not only spread in water bodies of Bengal but also throughout India.

Question. Why lichens are regarded as pollution indicators ? 
Answer : Lichens are very sensitive to air pollution particularly caused by SO2. Air pollution due to SO2 destroy lichen population. They do not grow in such a polluted area. Therefore, they are regarded as indicators of pollution. 

Short Answer Type Questions – ll

Question. (i) Name any two places where it is essential to install electrostatic precipitators. Why is it required to do so ?
(ii) Mention one limitation of the electrostatic precipitator. 
Answer : (i) Thermal power plants/smelters/other particulate matter releasing industries. To remove particulate matter. (Any two)
(ii) Very very small particulate matter/less than 2.5 micrometres are not removed/velocity of air between plates must be low enough to allow the dust to fall/cannot work without electricity.

Question. Presently, air quality of Delhi has significantly improved in comparison to what existed before 1997. This is the result of conscious human efforts. You are being asked to conduct an awareness programme in your locality wherein you will comment on the steps taken by Delhi Government to improve the air quality.
(i) Write any two of your comments.
(ii) List any two ways that you would include in your programme so as to ensure the maintenance of good quality of air.
(iii) State any two values your programme will inculcate in the people of your locality.
Answer : (i) (a) Use of CNG as fuel encouraged in vehicles.
(b) Improved public transport system like new fleet of DTC buses, Introduced Metro.
(c) Pollution check of vehicles was made mandatory.
(d) Availability of sulphur free fuel (Euro II norms). (Any other suitable value)
(ii) (a) Car pool essential
(b) Use of bicycle
(c) Get your car pollution checked regularly (Any other suitable example) (Any two)
(iii) (a) Consciousness about the environment increase plantation activity
(b) Concern for others
(c) Improving social skills
(d) Leadership quality

Question. “Determination of Biological Oxygen Demand (BOD) can help us in suggesting the quality of a water body.” Explain.
Answer : Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen required by the aerobic organisms to breakdown the organic material present in the water body at a certain temperature over a certain period of time. Natural water bodies contain a certain level of organic substances that are acted upon and decomposed by microbes. 
Determining the BOD of water body establishes the amount of organic content in it. Presence of more organic wastes increase the biological activity. Thus, leading to algal blooms. High BOD value indicates more microbial activity, indicating that the water body is polluted.

Question. With the help of a flowchart exhibit the events of Eutrophication.
Answer :
Enrichment of water body by excessive nutrients is called eutrophication. The events of eutrophication are as follows :

Question. Our farmers still use DDT. How is this affecting the local bird population ?
Answer : As a result of biomagnification, through an aquatic food chain, high concentration of DDT disturbs calcium metabolism in birds, which causes thinning of egg shell, and premature breaking, eventually leading to decline in bird population.

Question. Two types of aquatic organisms in a lake show specific growth patterns as shown below, in a brief period of time. The lake is adjacent to an agricultural land extensively supplied with fertilizers.

Answer the questions based on the facts given above :
(i) Name the organisms depicting the patterns A and B.
(ii) State the reason for the growth patterns seen in A.
(iii) Write the effects of the growth patterns seen  above. 
Answer : (i) A–algae / planktonic (free floating) algae B–fish / aquatic animals
(ii) Due to excessive loading of nutrients / fertilizers from adjacent agriculture land resulting in increase in nutrients.
(iii) Decrease in dissolved oxygen, increase in BOD, fish mortality, unpleasant odour / eutrophication.

Question. Explain how biomagnification of DDT occurs in an aquatic food chain.
With the help of a flowchart, show the phenomenon of biomagnification of DDT in an aquatic food chain. 
Answer : DDT in water taken up by an organism cannot be metabolised or excreted and thus passed on to successive trophic level in higher concentration.
Water (0.003 ppm) → Zooplankton (0.04 ppm) → Small fish (0.5 ppm) → Large fish (2 ppm) → Fish eating birds (25 ppm)

Question. How does a water body age naturally ? Explain.
State how this phenomenon of ageing of a water body gets accelerated.
Answer : The natural ageing of a lake is termed as eutrophication. In a young lake, the water is cold and clear, supporting little life. With time, streams
draining into the lake introduce nutrients such as nitrogen and phosphorus, which encourage the growth of aquatic organisms. As the lake’s fertility increase, plant and animal life flourishes, and organic remains begin to be deposited on the lake bottom. Over the centuries, as silt and organic debris pile up, the lake grows shallower and warmer, with warm-water organisms supplanting those that thrive in a cold environment. Marsh plants take root in the shallows and begin to fill in the original lake basin. Eventually, the lake gives way to large masses of floating plants (bog), finally converting into land. Depending on climate, size of the lake and other factors, the natural ageing of a lake may span thousands of years. Pollutants from man’s activities like effluents from
the industries and homes can radically accelerate the ageing process. This phenomenon is called cultural or accelerated eutrophication.
(i) When sewage is discharged into a river, micro-organisms involved in biodegradation of organic matter in the receiving water body consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. This causes mortality of fish and other aquatic organisms.
(ii) The presence of large amounts of nutrients in waters also causes excessive growth of planktonic algae, called an algal bloom, which imparts a distinct colour to the water bodies. Algal blooms cause deterioration of the water quality and causes fish mortality. Some bloomforming algae are extremely toxic to human beings and animals.

Question. Looking at the deteriorating air quality because of air pollution in many cities of the country, the citizens are very much worried and concerned about their health. The doctors have declared health emergency in the cities where the air quality is very severely poor.
(a) Mention any two major causes of air pollution
(b) Write any two harmful effects of air pollution to plants and humAnswer :
(c) As a captain of your school Eco-club, suggest any two programmes you would plan to organize in the school so as to bring awareness among the students on how to check air pollution in and around the school.
Answer : (a) Vehicular discharge / smoke from industries / burning of agricultural wastes / smoke from incinerator / dust / smoke from thermal plants or any other correct cause.
(b) Reduces growth of plants / reduces yields of crops / premature death of plants / respiratory problems / acid rain / any other relevant point.
(Any two – one from plant and one from human)
(c) Plantation drive / awareness programmes through posters / nukkad natak / film show / rallies / debates or any other.

Question. How does algal bloom destroy the quality of a fresh water body ? Explain.
Answer : The excessive growth of planktonic (free-floating) algae is called algal bloom. Nutrients present in sewage and fertilizers cause dense growth of plants and planktonic algae. Soon planktonic algae increase in number and impart a characteristic colouration to water. Algal bloom is toxic to animals and humAnswer : It blocks light for submerged plants. There is a drastic decrease in oxygen due to which animals die.

Question. Why should the spraying of DDT as an insecticide on vegetable crops be banned ?
Answer : DDT is insoluble in water but soluble in fats.
Due to low efficient transfer of energy from one trophic level to other, herbivores eat more DDT–polluted vegetables. Similarly, carnivores eat many herbivores. A predator stores much quantity of DDT with its prey continuously. This process continues for several years by which a significant concentration of DDT accumulates in top carnivores. DDT causes thinning of eggshells and their premature breaking, eventually causing decline in bird populations.

Question. Explain the effect on the characteristics of river when urban sewage is discharged into it.
Answer : (a) Rise in organic matter, leads to increased microbial activity / growth of microbes
(b) It results in decrease in dissolved oxygen / rise in Biochemical Oxygen Demand
(c) Leads to fish mortality / algal bloom / colour change / foul odour / increase in toxicity

Question. Particulate and gaseous pollutants alongwith harmless gases are released from the thermal power plants.
(i) Name any two harmless gases released.
(ii) Name the most widely used device for removing particulate pollutants from the air. Explain how the device is used ?
Answer : (i) CO2 & N2.
(ii) The most widely used device for removing particulate pollutant from air is the electrostatic precipitator. It has electrode wires and a stage of collecting plates connected electrically with earth. The particles occurring in polluted air are charged electrically. These charged particles are passed over collecting plates. These particles settle down after losing their charge.

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 : Use of CNG/Phasing out of old vehicles / Use of unleaded petrol / Use of low sulphur fuel / Use of catalytic converters / Application of stringent pollution level. 

Question. Explain any three measures which will control vehicular air pollution in Indian cities.
Answer : The vehicular air pollution is chiefly controlled by
(i) Promoting public transports like buses,metro trains,etc.
(ii) Use of low sulfur content petrol and diesel.
(iii) Use of Catalytic converters in vehicles which help in converting the pollutants to less toxic forms.

Question. Why is the concentration of toxins found to be more in the organisms occupying the highest trophic level in the food chain in polluted water body? Explain with the help of suitable example. 
Answer : Concentration of toxins is more in organisms occupying the highest trophic level in the food chain. It is because of biomagnification. It goes on increasing at each trophic level of a food chain and is therefore maximum in the organisms of highest trophic level due to their increasing accumulation at each trophic level. For example DDT was used to control mosquitoes in a lake of USA. It was noted that the DDT found in phytoplantktons was about 800 times higher than that present in the lake and zooplanktons had about 13 times more DDT than that in phytoplanktons.

Question. A young sperm whale, 33-foot long was found dead off the coast. It had a large amount of human trash like trash bags, polypropylene sacks, ropes, net segments etc. amounting to 29 kilograms in its digestive system. The whale died because of inflammation of the abdominal lining. Analyze the possible reasons for such mishaps and suggest measures that can be taken to reduce such incidents.
Answer : Due to cheap and quick production, durability and usefulness in several applications, plastic has become desired material for creating objects like trash bags, polypropylene sacks, ropes, net segments. But plastic is non-biodegradable product and extremely harmful. These plastic products get transported to nearby rivers and to oceAnswer : These products are swallowed by marine animals mistaken it to be a food. Thus, plastic, once ingested, cannot be digested or passed by an animal so it stays in the gut leading to their death. Measures that could be taken to reduce such mishaps are:
(a) We can support government’s initiative across the country for reducing the use of plastics and use of eco-friendly packaging.
(b) We can do our bit by carrying cloth or other natural fibre carry-bags when we go for shopping and by refusing to take the polythene bags from shopkeepers.
(c) It is important that all garbage generated is sorted. The biodegradable materials can be put into deep pits in the ground and be left for natural breakdown. It leaves only the non-biodegradable to be disposed of, the quantity of which should be minimized. The need to reduce our garbage generation should be a prime goal.

Long Answer Type Questions

Q. 1. (i) Public transport in Delhi uses CNG since 2002. List the advantages of this fuel policy.
(ii) BOD was measured in two different places A and B of a river in the direction of its flow. BOD value was higher at A than B. What do you infer from this observation and why ?
Answer : (i) Delhi Government shifted to CNG (Compressed Natural Gas) because :
(a) It burns more efficiently, unlike petrol or diesel, in automobiles and very little of it is left unburnt.
(b) CNG is cheaper than petrol and diesel.
(c) It cannot be siphoned off by thieves.
(d) It cannot be adulterated like petrol or diesel.
(ii) Biochemical oxygen demand (BOD) refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria. As the BOD value is higher at A, therefore, the amount of dissolved oxygen is lower in that place.
Excessive growth of algae, plants and animals in water bodies due to the nutrient enrichment, particularly with nitrogen and phosphorus, and discharge of domestic sewage into a river results in the rise of BOD. However, as the organic matter is decomposed, there is a gradual rise in the amount of dissolved oxygen downstream.

Q. 2. A national newspaper reported that a 50 metre high ‘Sanitary landfill’, the dumping site of city’s garbage in one of the metro-cities crashed and caused heavy damage and disaster in and around the area. A couple of cars, two-wheelers and cattle were swept away in the nearby overflowing canal. Three persons including a young girl were crushed under the garbage and died.
(a) Write any two points that in your opinion could
have caused this landfill crash.
(b) Mention any four preventive measures to be adhered to as a policy which could have avoided this accident.
(c) Write any two suggestions that you would like to give to the citizens so as to help in preventing such a disaster in future.
Answer : (a) Lack of proper waste management measures, overloading of landfill area 
(b) Prevent overloading of any designated landfill, litter control through covering material/ soil regularly, litter load should be compacted, create temporary / permanent fencing, regular monitoring of landfill area, engineers to design landfills habitat (any other appropriate points) 
(c) Reduce use of disposable material, recycle waste as much as possible, start making compost pile for food scraps, use reusable fabric shopping bags, avoid creating trash