Environmental Issues Class 12 Biology Important Questions

Important Questions Class 12

Please refer to Environmental Issues Class 12 Biology Important Questions with solutions provided below. These questions and answers have been provided for Class 12 Biology based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 12 Biology for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 12.

Class 12 Biology Important Questions Environmental Issues

Very Short Answer Questions

Question. Why is Eichhornia crassipes nicknamed as “Terror of Bengal”? 
Ans. 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 an industry which can cause air pollution, thermal pollution and eutrophication.
Ans. Fertiliser factory.

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

Question. In spite of being non-polluting, why are there great apprehensions in using nuclear energy for generating electricity? 
Ans. There are great apprehensions in using nuclear energy because of accidental leakages and finding ways for safe disposal of radioactive waste.

Question. How do algal blooms affect the life in water bodies? 
Ans. (i) Algal bloom pollutes water and deteriorates the water quality by depleting the oxygen content. This turns the water toxic and increases its BOD.
(ii) Algal blooms lead to death of aquatic organisms due to oxygen depletion.

Question. How do plants control pollution?
Ans. Plants absorb and assimilate the pollutants like CO2 and provide oxygen by the process of photosynthesis. This reduces the pollution.

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

Question State the effect of UV-B on human eye.
Ans. UV-B is absorbed by human eye and at high dose, it causes inflammation of cornea. This is called snow-blindness cataract.

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

Short Answer Questions

Question. Explain the relationship between green house gases and global warming. 
Ans. Greenhouse gases (CO2, CH4, N2O, CFCs) allow the solar radiations to enter but prevent the escape of heat radiations of longer wavelength. The absorbed radiations again come to earth’s surface and heat it up. Increase in the level of these greenhouse gases allow the heat waves to reach earth but prevent their escape and thus the earth becomes warm. There is gradual continuous increase in average temperature of earths’ surface leading to global warming.

Question. Explain the relationship between CFCs and ozone in the stratosphere. 
Ans. UV rays act on CFCs and release chlorine. These chlorine atoms act on ozone to release O2,resulting in ozone layer depletion.

Question. List four benefits to human life by eliminating the use of CFCs. 
Ans. (i) Delay in aging of skin (ii) Prevent damage to skin cells
(iii) Prevent skin cancer (iv) Prevent snow blindness or inflammation of cornea
(v) Prevent cataract (vi) Prevents ozone depletion
(vii) Prevents global warming (viii) Reduces greenhouse effect
(ix) Reduces odd climatic changes or El Nino effect. (Any four)

Question. Chlorofluorocarbons (CFCs) are widely used as refrigerants. Then why is it suggested to reduce its emission as far as possible? Explain. 
Refrigerants are considered to be a necessity in modern living, but are said to be responsible for ozone holes detected in Antarctica. Justify. 
Ans. 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.

Question5. Why are there regular reminders to reduce the use of CFCs in the production of industrial and household appliances? Explain.
Ans. 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. 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.
Ans. Yes, the water will become septic if the dissolved oxygen drops to zero. Organic pollution (biodegradable) is an example.

Question. (a) State the cause of depletion of ozone layer.
(b) Specify any two ill-effects that it can cause in the human body.
Ans. (a) UV radiations act upon CFCs (chlorofluorocarbons) releasing Cl atoms in the stratosphere. These Cl atoms combine with O3 and degrade it.
(b) Ill-effects of ozone depletion:
(i) UV-B damages DNA and proteins of living organisms causing mutation.
(ii) It causes skin aging, skin cell damage and skin cancers.
(iii) UV-B is absorbed by human eye and at high dose it causes inflammation of cornea. This is called snow-blindness cataract.

Question. Match the items given in column A and B.
Column A Column B
(a) Catalytic converter (i) Particulate matter
(b) Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides
(c) Earmuffs (iii) High noise level
(d) Landfills (iv) Solid wastes
Ans. (a)–(ii), (b)–(i), (c)–(iii), (d)–(iv).

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. 
Ans. (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.
Ans. 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? 
Ans. The plant growing near the boundary wall act as barrier for sound pollution and act as dust catchers.

Long Answer Questions

Question. Why is the concentration of toxins found to be more in the organisms occupying the highest trophic level in the food chain in a polluted water body? Explain with the help of a suitable example. 
Ans. The concentration of toxic materials like heavy metals and pesticides increase at each trophic level of a food chain and is more in organisms of highest trophic level due to their accumulation at each trophic level. For example, when DDT was used to control mosquitoes in a lake of USA, 800 times more DDT was found in the phytoplanktons than in the water of the lake. Zooplanktons had about 13 times more DDT than phytoplanktons. It was also observed that the fishes population had 9–40 times more DDT than zooplanktons and fish eating birds had 25 times more DDT than fish.

Question. Mention the six harmful effects of noise on human health.
Ans. Six harmful effects of noise on human population are:
(ii) Harmful effects (Psychological and Physiological disorders)
(a) Sleeplessness
(b) Stress
(c) Increased rate of heartbeat and hypertension
(d) Breathing problems
(e) Damage of ear drums impairing hearing ability permanently (by the sound of jet plane/rocket or chronic exposure to sound).
(f) Gastric problems—nausea
(g) Emotional disturbance

Question. Write critical notes on the following:
(a) Eutrophication (b) Biological magnification
(c) Groundwater depletion and ways for its replenishment.
Ans. (a) Eutrophication:
 Marsh plants take root in the shallows and begin to fill in original lake basin.
 Eventually, floating plants develop in the lake, finally converting it into land.
 According to climate, size of the lake and other factors, natural ageing of lake may span up to thousands of years.
 The accelerated aging of lakes due to sewage, agricultural and industrial wastes is called cultural or accelerated eutrophication.
(b) Biological magnification: Unknowingly some harmful chemicals enter our bodies through the food chain. We use several pesticides and other chemicals to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the topmost level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies. This phenomenon is known as biological magnification.
(c) Groundwater depletion and ways for its replenishment: Groundwater is depleting due to various reasons like deforestation, agricultural use, daily use at home, etc. Groundwater level is going down in several states due to its unjudicious use. Replenishment of groundwater can be done by rainwater harvesting and reforestation. Rainwater can be collected on the roof top of the buildings and can be stored underground for later use.

Question. (a) Expand BOD.
(b) At a particular segment of a river near a sugar factory, the BOD is much higher than the normal level. What is it indicative of? What will happen to the living organisms in this
part of the river?
(c) Under what conditions will the BOD be lowered in the river? How will it affect the aquatic life? 
Ans. (a) BOD—Biochemical Oxygen Demand
(b) It indicates the addition of lot of organic matter; microorganisms involved in the biodegradation of organic matter in the water body consume a lot of oxygen and as a result, there is a sharp decline in the dissolved oxygen content, downstream from the point of addition of effluent from the factory. This causes mortality of fish and other aquatic organisms.
(c) When the amount of organic matter decreases and the microbes do not need oxygen for decomposition, the BOD decreases. Thus, aquatic organisms will start flourishing.

Question. What is global warming? List four strategies for reducing global warming.
Ans. Increase in the level of greenhouse gases in the atmosphere causes rise in global mean temperature called global warming.
Four strategies for reducing global warming are: Control of global warming
 Global warming can be controlled by:
(a) Reducing deforestation
(b) Planting trees (afforestation)
(c) Slowing down the growth of human population
(d) Reduction of emission of greenhouse gases into the atmosphere
(e) Cutting down use of fossil fuels
(f) Improving efficiency of energy usage.

Question. Explain the causes of global warming. Why is it a warning to mankind?
Ans. Causes of global warming:
(i) Deforestation
(ii) Rise in the concentration of greenhouse gases (CO2, CH4, CFCs, N2O).
(iii) Burning of fossil fuels
(iv) Rise in industrial wastes and pollutants.
Global warming is a warning to mankind because:
(i) Rise in temperature is leading to increased melting of polar ice-caps as well as of other places like the Himalayan snow caps. This will result in a rise in sea level that can submerge many coastal areas.
(ii) Deleterious changes in the environment results in odd weather and climate changes, e.g.,El Nino effect.

Question. A plastic sack manufacturer in Bengaluru, Ahmed Khan has managed to find an ideal solution to the problem of plastic waste. Explain in five steps the efforts of Ahmed Khan to meet the challenges of solid waste management. 
Ans. (i) Ahmed Khan developed polyblend, which is a fine powder of recycled modified plastic.
(ii) Polyblend is mixed with bitumen and used to lay roads. This work is done in collaboration with R V engineering college and Bangalore city corporation.
(iii) Polyblend enhanced water-repellant property of bitumen and increase the road life.
(iv) Khan offered a price to rag pickers which enhanced their income and improved their livelihood.
(v) Thus solid waste management was achieved by removal and proper disposal of plastic waste from the city.

Environmental Issues Class 12 Biology Important Questions