VBQs Environmental Issues Class 12 Biology

VBQs for Class 12

VBQs Environmental Issues Class 12 Biology with solutions has been provided below for standard students. We have provided chapter wise VBQ for Class 12 Biology with solutions. The following Environmental Issues Class 12 Biology value based questions with answers will come in your exams. Students should understand the concepts and learn the solved cased based VBQs provided below. This will help you to get better marks in class 12 examinations.

Environmental Issues VBQs Class 12 Biology

Very Short Answer Type Questions

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

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

Short Answer Type Questions

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. 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. 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.

VBQs Environmental Issues Class 12 Biology

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 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. 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.
Detailed Answer :
(i) Presence of large amount of nutrients in water causes excessive growth of planktonic (free – floating) algae, called an algal bloom. Algal blooms cause deterioration of water quality and fish mortality. Some bloom forming algae are extremely toxic to human beings and animals.
(ii) Treatment of waste water before reaching pond by integrated water treatment is the preventive measure.

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. (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. 
Detailed Answer :
(i) In thermal power plants and automobile vehicles. It is because, electrostatic precipitator can remove particulate matter from their exhaust.
(ii) One of the major limitations of electrostatic precipitator is that it cannot remove particulates which are 2.5 micrometers or less in diameter, which may cause respiratory symptoms.

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 resent 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 :

VBQs Environmental Issues Class 12 Biology

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.

VBQs Environmental Issues Class 12 Biology

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. 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. 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
Detailed Answer:
When organic wastes from the urban sewage enter the water bodies it serves as a food source for microorganisms such as algae and bacteria. As a result, the population of these microorganisms in the water body increases. Here, they utilize most of the dissolved oxygen for their metabolism. This results in increase in the levels of Biodegradable oxygen demand (BOD) in river water and results in the death of aquatic organisms. Also, the nutrients in the water lead to the growth of planktonic algae, causing alga bloom. It imparts a distinct colour to the water bodies and deteriorates the water quality resulting in death of fishes. Some bloom-forming algae are extremely toxic to human being and animals. 

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. 

Long Answer Type Questions

Question. 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 (any other appropriate measure)