VBQs Class 12 Biology Environmental Issues

Please refer to VBQs for Class 12 Biology Environmental Issues. All value based questions for Biology Class 12 have been provided with solutions. We have provided below important values questions and answers. Students should learn these solved VBQs for Class 12 Biology as these will help them to gain more marks and help improve understanding of important topics.

Environmental Issues VBQs Class 12 Biology with Answers

Air Pollution and its Control

Very Short Answer Type Questions

Question. List two advantages of the use of unleaded petrol in automobiles as fuel. 
Answer. Two advantages of using unleaded petrol in automobiles as fuel are:
(i) Unleaded petrol results in decline in the emission of harmful gases such as SO₂, CO and NO₂, thereby improving air quality.
(ii) It is desirable to use unleaded petrol in the automobiles fitted with catalytic converter because lead in the petrol inactivates the catalyst metals like platinum-palladium and rhodium, etc. present in the converter. 

Question. Why are lichens regarded as pollution indicators? 
Answer. Lichens are very sensitive to pollution, especially caused by SO₂. Air polluted with SO₂ and acid rain, destroy lichen population.

Question. Mention two advantages for preferring CNG over diesel as an automobile fuel. 
Answer. CNG is preferred over diesel because it burns more eficiently without producing much pollution and it cannot be adulterated like diesel.

Question. List two gaseous products that are produced when exhaust of an automobile passes though a catalytic converter. 
Answer. Carbon monoxide and nitrogen oxide. 

Short Answer Type Questions

Question. Name two metals used in a catalytic converter.How do they help in keeping the environment clean? 
Answer. Metals used in catalytic converters are platinum-palladium and rhodium. When exhaust gas is passed through catalytic converter, unburnt hydrocarbons are oxidised to produce carbon dioxide and water. Carbon monoxide is oxidised to form carbon dioxide and nitrogen oxide splits up to form nitrogen gas.
Thus, help in keeping the environment clean.

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. Thermal power plants release particulate and gaseous air pollutants into the atmosphere. These pollutants can be separated by the use of electrostatic precipitators.

Question. How does an electrostatic precipitator work to remove particulate pollutants released from the thermal power plants? 
Answer. Electrostatic precipitator is the most eficient device which is used to separate particulate pollutants. It has electrode wires and a stage of collecting plates. The particles present in dirty air are charged electrically to form a corona of negative charges around them. The charged dust particles are passed over collecting plates connected electrically with earth. Dust particles lose their charge and settle down.

Question. Mention the major cause of air pollution in metro cities. Write any three ways by which it can be reduced.
Answer. The main sources of air pollution are motor vehicles, industries, fossil fuel (coal) based plants and thermal power plants. It can be controlled by: (i) use of low sulphur fossil fuel, (ii) zoning of industries away from human settlements for dispersing pollution sources, (iii) changing pollutants to less toxic forms.

Question. Public transport in Delhi uses CNG since 2002. List the advantages of this fuel policy.
Answer. CNG (compressed natural gas) is a better fuel than petrol or diesel because it is cheaper, burns more eficiently, does not produce much pollution, cannot be siphoned off by thieves and it cannot be adulterated like petrol and diesel.

Question. How do automobile fitted with catalytic converters reduce air pollution? Suggest the best fuel for such vehicles. 
Answer. Automobiles fitted with catalytic converters have costly metals like platinum-palladium and rhodium as catalysts. They convert harmful gases into less toxic form. Unburnt hydrocarbons are oxidised to produce carbon dioxide and water. Carbon monoxide is also oxidised to form carbon dioxide. However, nitrogen oxide splits up to form nitrogen gas. Catalytic converter fitted automobiles should use unleaded petrol because lead in the petrol inactivates the catalyst. Use of multipoint fuel injection engines are best for such vehicles. 

Short Answer Type Questions

Question. (a) State the consequence if the electrostatic precipitator of a thermal plant fails to function.
(b) Mention any four methods by which the vehicular air pollution can be controlled.
Answer. 
(a) If the electrostatic precipitator fails to function, then smokestacks of thermal power plants, smelters and various industries will release particulate and gaseous air pollutants. The emission will also possess hot air with harmless gases, such as nitrogen, oxygen etc. Therefore, smoke containing fine particulate and gaseous pollutants will not be filtered. This situation will cause air pollution that will affect all living organisms including various human respiratory problems.
(b) The four methods for controlling vehicular air pollution are as follows:
(i) Use of CNG (Compressed Natural Gas)
(ii) Use of catalytic converters in vehicles
(iii) Use of low sulphur petrol and diesel
(iv) Application of stringent pollution level norms of vehicles etc.

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) The major sources of the particulate matter are industrial and thermal power plant exhausts. Therefore, it is essential to install electrostatic precipitators in industries and thermal power plants. Electrostatic precipitators are very eficient devices that can remove over 99 per cent particulate matter present in exhaust.
(b) One of the major drawbacks of electrostatic precipitator is that it cannot remove particulate matter of less than 2.5 micrometre diameter, which causes various respiratory problems.

Question. Particulate and gaseous pollutants along with harmless gases are released from the thermal power plants.
(a) Name any two harmless gases released.
(b) Name the most widely used device for removing particulate pollutants from the air. Explain how the device is used.
Answer.(a) CO₂ and N₂
(b) Electrostatic precipitator is the most eficient device which is used to separate particulate pollutants. It has electrode wires and a stage of collecting plates. The particles present in dirty air are charged electrically to form a corona of negative charges around them. The charged dust particles are passed over collecting plates connected electrically with earth. Dust particles lose their charge and settle down.

Question. Presently, air quality of Delhi has significantly improved in comparison to what existed before 1997. This is the result of a lot 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.
(a) Write any two of your comments.
(b) List any two ways that you would include in your programme so as to ensure the maintenance of good quality of air.
(c) State any two values which your programme will inculcate in the people of your locality
Answer. (a) (i) It was necessary and a very effective step taken by Delhi Government to switch over the entire fleet of public transport to compressed natural gas (CNG), as CNG causes less pollution in comparison to petrol or diesel.
(ii) Compulsory regular checkup of pollution emission of vehicles also add to reduction in vehicular air pollution.
(b) (i) Use of unleaded petrol, low-sulphur petrol/ diesel must be insisted.
(ii) Switching over from diesel/petrol to compressed natural gas (CNG) and making compulsory the use of catalytic converter in vehicles.
(c) The two values that the programme will inculcate in the people of locality are:
(i) Cooperation and sharing of vehicles to reduce vehicular air pollution e.g., car pooling.
(ii) Awareness about the extent of environmental pollution by automobiles.

Water Pollution and its Control

Very Short Answer Type Questions

Question. Name the world’s most problematic aquatic weed. What is the nature of the water body in which the weed grow abundantly?
Answer.Eichhornia crassipes is a problematic aquatic weed. It grows in the water body which is rich in nutrients specially nitrogen and phosphorus.

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

Question. Mention the information that the health workers derive by measuring BOD of a water body. 
Answer. BOD (biochemical oxygen demand) is the amount of the oxygen required by microorganisms to decompose the organic matter present in one litre of water during a particular time period. BOD test measures degree of impurity of water. As higher the BOD, more will be the pollution. Thus, indirectly BOD is a measure of the organic matter present in the water.

Question. Why is Eichhornia crassipes nicknamed as ‘Terror of Bengal’? 
Answer. Eichhornia crassipes is also called as “Terror of Bengal” because it sometimes chokes ponds, lakes and rivers resulting in imbalance of ecosystem of water bodies and causes death of aquatic animals.

Question. Excessive nutrients in a freshwater body cause fish mortality. Give two reasons. 
Answer.(i) Passage of sewage and run off from fertilised fields into water bodies results in excessive nutrients which causes excessive growth of algae. The algae use oxygen at night and deoxygenate the water enough to kill fish and other animals.
(ii) Eutrophic water bodies support excessive growth of floating plants, which cut off light for submerged plants and latter die. This results in decrease in oxygen content and cause death of fish.

Question. How do algal blooms affect the life in water bodies?
Answer. Excess growth of planktonic algae is called algal blooms. They are toxic to animals and humans. Algal blooms cut off light from submerged plants causing their death. There is decrease in oxygen in water that deteriorates the water quality and kills aquatic animals

Question. State the cause of accelerated eutrophication.
Answer. Eutrophication is the natural ageing of a lake or water bodies by nutrient enrichment of water. Apparently pollutants from human activities like efluents from the industries and homes such as sewage, agriculture wastes, etc. have radically accelerated this ageing process. This phenomenon is called accelerated eutrophication.

Short Answer Type Questions

Question. ‘Fish mortality increases with influx of nutrients in a fresh-water body’. Write two reasons. How will the influx of nutrients affect the BOD level of this water body? 
Answer. Excessive nutrients in a fresh water body cause fish mortality because of the following two reasons:
(i) Excessive nutrients cause dense growth of floating plants and planktonic algae (algal bloom) which cut off light from submerged plants and the latter die.
(ii) Increase in nutrients reduces dissolved oxygen and increases biochemical oxygen demand (BOD) of water body, leaving nothing for respiration of fish and therefore, they get killed. Algal blooms formed by some blue green algae are toxic to aquatic animals and humans.
Influx of nutrients would increase the BOD level of water body, because more oxygen would be required by microorganisms to metabolise organic wastes.

Question. Explain how does the algal bloom eventually choke the water body in an industrial area.
Answer. The nutrient enrichment of water bodies near industrial area is due to passage of industrial effuents, sewage etc. This cause dense growth of planktonic algae that causes colouration of water called algal bloom. Excessive growth of it cut off light for submerged plants which kills the latter and causes organic loading. This leads to decreased oxygen level which eventually chokes the water body.

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

Answer. When sewage containing organic waste is discharged into the river, the microorganisms consume a large amount of oxygen for the decomposition of organic matter, hence, there is a sharp decline in the dissolved oxygen content of water downstream from the point of sewage discharge. But after a short distance, when the quantity of organic matter is reduced, the demand of oxygen by the decomposers also reduce and there is gradual rise in dissolved oxygen downstream.

Question. 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 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. The concentration of DDT in birds has increased because it is a toxic, non-biodegradable substance and it cannot be excreted or metabolised and is passed on to the next higher trophic level. During the transfer along food chain, its concentration in tissues increases. This is why its highest concentration is found in fish eating bird kingfisher which occupies the highest tropic level. This will result in decline in bird population. The phenomenon is called biological magnification.

Question. Explain the cause of algal bloom in a water body. How does it affect an ecosystem?
Answer. Algal bloom occurs due to presence of excess nutrients especially phosphates and nitrates in the water body. The growth of algal blooms will result in depletion of oxygen level in the water body, killing fishes and other aquatic animals and plants.

Question. Why is it dificult to get rid of ‘water-hyacinth’ from a water body? Name one abiotic component and one biotic component of the ecosystem that get affected by its spread in the water body.
Answer. It is dificult to get rid of ‘water-hyacinth’ from water body because eutrophic water bodies support excessive growth of water hyacinth, a floating plant, also called ‘Terror of Bengal’. Abiotic and biotic components affected by spread of water hyacinth are light and submerged plants respectively, as its growth cuts off light for submerged plants.

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

Answer. Due to the discharge of sewage into the river, the microorganisms present in the river get involved in biodegradation of organic matter of sewage, as a result a lot of oxygen is consumed.
The peak ‘a’ shows a sharp rise in level of biological oxygen demand due to decline in dissolved oxygen downstream from the point of sewage discharge. The peak ‘b’ shows a gradual increase in the dissolved oxygen, as sewage gets decomposed and BOD level decreases.

Question. 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 at B. What do you infer from this observation and why?
Answer. As BOD is higher at A in river, so it indicates high level of pollution at A. It might be due to fact that point of discharge of domestic sewage is located near A. Discharge of domestic sewage into a river will result in rise of BOD because decomposers consume a lot of oxygen for metabolising organic wastes. If sewage quantity is large, the whole of dissolved oxygen may be consumed leaving nothing for respiration of fish and other clean water organisms and therefore, they get killed. As sewage is decomposed, towards B, there is gradual rise in dissolved oxygen downstream. Fish and other clean water organisms reappear indicating recovery of river from sewage pollution.

Question. A crane had DDT level as 5 ppm in its body. What would happen to the population of such bird? Explain giving reasons.
Answer. The population of birds with high DDT level will decrease. High concentration of DDT disturbs calcium metabolism in birds which causes thinning of egg shell and their premature breaking. This will eventually lead to decline in bird population.

Question. Explain how does the inflow of large amount of nutrients like phosphates and nitrates into the water body drastically affcts the aquatic life there. Name the phenomenon responsible.
Answer. Passage of sewage and run off from fertilised fields into water bodies causes nutrient enrichment particularly with nitrogen and phosphorus. Nutrients present in sewage and fertilisers cause dense growth of plants and planktonic algae. The algae use oxygen at night and may deoxygenate the water enough to kill the fish and other animals. The excess growth of planktonic algae that imparts a distinct colour to water bodies is called algal bloom. They are toxic to animals and humans. Algal blooms and floating plants cut off light from submerged plants and the latter die. There is drastic decrease in oxygen replenishment inside water. It causes organic loading of water and death of fish and other animals. The phenomenon responsible for this is eutrophication.

Short Answer Type Questions

Question. With the help of flowchart exhibit the events of eutrophication. 
Answer. Eutrophication is the natural ageing of a water body by nutrient enrichment of its water. The flow chart exhibiting the events of eutrophication in a lake are given below:
Young lake (water is cold and clear)
   ↓
Streams and agricultural run offs drains into the lake and introduce nutrients like N2, P etc.
   ↓
Fertility of lake increases due to added nutrients.
   ↓
Encourages growth of aquatic plant and animal life.
   ↓
Organic remains are deposited at the bottom of the lake.
   ↓
Over centuries, the lake becomes shallower and warmer.
   ↓
Marshy plants grow and fill in the original lake basin.
   ↓
Large masses of floating plant.
   ↓
Lake is converted into land.

Question. Explain biomagnification of DDT in an aquatic food chain. How does it affect the bird population? 
Answer. Biomagnification is continuous increase in concentration of insecticide and pesticide in successive trophic levels in a food chain. Regular DDT spray for a few years, resulted in drastic decline in the population of fish eating birds. There was 1000 times increase in concentration of DDT in phytoplankton as compared to water, in zooplankton as compared to phytoplankton, in different fish as compared to zooplankton and more DDT in fish eating birds as compared to fish. Higher amounts of pesticide disturb calcium metabolism of birds resulting in thinning of egg shells and their premature breaking that kills the embryos.

Question. Explain the changes that can be observed in the characteristics of river water when sewage is discharged into it and a few weeks aer the discharge with respect to :
(a) level of dissolved oxygen
(b) population of fresh water organisms.
Answer. 
(a) Discharge of domestic sewage into a river will result in rise of BOD because decomposers consume a lot of oxygen. If sewage quantity is large, then whole of dissolved oxygen will be consumed the leaving nothing for aquatic organisms. However, as sewage is decomposed, there will be gradual rise in dissolved oxygen downstream.
(b) With depletion in level of dissolved oxygen, population of fresh water organisms would decline.
But, as levels of dissolved oxygen would increase, fish and other aquatic organisms reappear indicating the recovery of river from sewage pollution.

Question. With the help of a flow chart, show the phenomenon of biomagnification of DDT in an aquatic food chain. 
Answer. DDT keeps on moving from water to different living components of the ecosystem and DDT concentration continuously increases in successive trophic levels in a food chain. This phenomenon is known as biological magnification or biological amplification. The flow chart showing biomagnification of DDT in an aquatic food chain is given below:

Question. A factory drains its waste water into the nearby lake. It has caused algal bloom.
(a) How was the algal bloom caused?
(b) What would be the consequences?
(c) Name the phenomenon that caused it.
Answer. (a) As the factory drains waste water into the lake, nutrient level (nitrogen and phosphorous) of the lake increases. Presence of large amount of nutrients in lake causes excessive growth of planktonic algae, called algal bloom.
(b) Algal bloom cut off light for submerged plants,thus leading to their death. This causes decrease in oxygen level in water which leads to organic loading of water. Decreased oxygen level also kills aquatic animals, further adding to organic loading.
(c) Eutrophication

Question. Drinking water problem in our urban areas is caused mainly because we fail to protect our water bodies. Explain how accelerated eutrophication chokes our water bodies to death.
Answer. Accelerated eutrophication is nutrient enrichment of water bodies due to human activities like passage of sewage, industrial effluents and run off from fertilised fields rich in nitrates and phosphates. Nutrients present in sewage, agricultural wastes and fertilisers cause dense growth of plants and planktonic algae. They support a good number of animals. The excess growth of planktonic algae that causes colouration of water is called algal bloom. They are toxic to animals and humans. In some cases eutrophic water bodies support excessive growth of floating plants e.g., water hyacinth (Eichhornia crassipes). Algal blooms and floating plants cut off light for submerged plants. The latter die. There is drastic decrease in oxygen replenishment inside water. It causes organic loading of water. Decreased oxygen level also kills aquatic animals, further adding to organic loading. Decomposition is replaced by putrefaction which is anaerobic. It produces secondary pollutants that kill the bloom forming plants as well and thus choking water bodies to death.

Question. Two type 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 fertilisers.

Answer the questions based on the facts given above:
(a) Name the organisms depicting the patterns A and B.
(b) State the reason for the growth pattern seen in A.
(c) Write the effects of the growth pattern seen above.
Answer.(a) A-Planktonic algae, decomposers.B-Fish, other aquatic animals.
(b) The growth of planktonic algae and decomposers is due to the presence of large amount of nutrients like nitrogen and phosphorus in water body.
(c) The growth of planktonic algae (algal bloom) causes deterioration of water quality and fish mortality. The decomposers acting on the dead plants and animals (organic matter) consume a lot of oxygen (increased BOD) and this further causes mortality of fish and other aquatic animals.

Question. How does an algal bloom cause eutrophication of a water body? Name the weed that can grow in such a eutrophic lake. 
Answer. Excessive nutrients cause dense growth of floating plants and planktonic algae (algal bloom) which cut off light for submerged plants. The latter die thereby causing organic loading which increases biochemical oxygen demand (BOD) of water and in turn reduces dissolved oxygen content of water. Decreased oxygen level kills many aquatic animals including fish. Algal bloom formed by some blue green algae are toxic to aquatic animals like fish etc. Eichhornia crassipes is the weed which grows in eutrophic lake.

Question. How does a water body age naturally? Explain. State how this phenomenon of ageing of a water body gets accelerated.
Answer. Eutrophication is the natural ageing of a water body by nutrient enrichment of its water, for example 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 increases, plant and animal life burgeons and organic remains begin to be deposited at 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. However, pollutants from human activities like effluents from the industries and homes can radically accelerate the ageing process. This phenomenon has been called cultural or accelerated eutrophication. During the past century, lakes in many parts of the earth have been severely eutrophied by sewage and agricultural and industrial wastes. The prime contaminants are nitrates and phosphates, which act as plant nutrients. They overstimulate the growth of algae, causing unsightly scum and unpleasant odours, and robbing the water of dissolved oxygen vital to other aquatic life.

Solid Wastes

Short Answer Type Questions

Question. How does Ahmed Khan, plastic sacks manufacturer from Bangalore, solve the ever increasing problem of accumulating plastic waste? 
Answer. Ahmed Khan of Bangalore came up with a remedy for eficient use of plastic waste. He developed polyblend, a fine powder of recycled modified plastic. This mixture is mixed with bitumen that is used to lay roads. In collaboration with R.V. College of Engineering and the Bangalore City Corporation, Ahmed Khan proved that blends of polyblend and bitumen, when used to lay roads, enhanced the bitumen’s water repellant properties, and helped to increase road life by a factor of three. The raw material for creating polyblend is any plastic film waste. Using Khan’s technique, by the year 2002, more than 40 kms of road in Bangalore has already been laid. At this rate, Khan will soon be running short of plastic waste in Bangalore, to produce polyblend.

Question. Name any two sources of electronic wastes. Mention any one way each of its disposal in developing and developed countries.
Answer. Irreparable computers and other electronic goods are sources of electronic wastes. Developed countries have specifically built facilities for recycling of electronic wastes. In developing countries, recycling of electronic wastes involves manual participation of workers, which exposes them to toxic substances present in e-wastes.

Question. Name any two sources of e-wastes and write two different ways for the disposal.
Answer.E-wastes or electronic wastes are generated from electronic appliances. It includes broken mobile phones, televisions, irreparable computers, etc. Sources of e-wastes come from a vast area of our daily life as each and every field is dependent on electronic appliances.
Two ways of disposal of e-wastes include –
(i) incineration
(ii) landfilling.

Question. Mention how e-waste is produced and disposed off. Write the solution for its treatment.
Answer. E-wastes are irreparable computers, mobiles and other electronic goods. Electronic wastes are generally sent to developing countries like India, China and Pakistan for extraction of metals through recycling. E-waste should be disposed off in landfills or should be incinerated. Recycling is the only solution for the treatment of e-waste, provided it is carried out in an environment-friendly manner.

Short Answer Type Questions

Question. (a) Why are the colourful polysterene and plastic packaging used for protecting the food,considered an environmental menace?
(b) Write about the remedy found for the eficient use of plastic waste by Ahmed Khan of Bangalore. 
Answer. (a) Colourful polysterene and plastic packaging used for protecting food to attract customers should be banned as these are non-biodegradable and persist in the environment for years and causes environmental pollution.
(b) Ahmed Khan of Bangalore came up with a remedy for eficient use of plastic waste. He developed polyblend, a fine powder of recycled modified plastic. This mixture is mixed with bitumen that is used to lay roads. In collaboration with R.V. College of Engineering and the Bangalore City Corporation, Ahmed Khan proved that blends of polyblend and bitumen, when used to lay roads, enhanced the bitumen’s water repellant properties, and helped to increase road life by a factor of three. The raw material for creating polyblend is any plastic film waste. Using Khan’s technique, by the year 2002, more than 40 kms of road in Bangalore has already been laid. At this rate, Khan will soon be running short of plastic waste in Bangalore, to produce polyblend.

Question. A few residents in your locality, for business gains, have established small-scale industrial/ commercial activities such as pathological labs and fabric dyeing centres without obtaining ‘No objection certificates’ from municipal authorities.
Would you support these activities? Give any three reasons in support of your answer.
Answer. 
Setting up of industries in residential localities without obtaining ‘No objection certificate’, from municipal authorities should be discouraged as effluents from industries contain number of poisonous organic compounds and toxic heavy metals like mercury, cadmium, copper etc. These chemicals enter into water bodies, and from water into all forms of life, leading to death of aquatic animals. These chemicals undergo biomagnification and affect human beings also, as they cause various disorders like mental retardation, skin cancer, leukaemia, nervous disorder etc.

Question. Community service department of your school plans a visit to a slum area near the school with an objective to educate the slum dwellers with respect to health and hygiene.
(a) Why is there a need to organise such visit?
(b) Write steps you will highlight, as a member of this department in your interaction with them to enable them to lead a healthy life.
Answer. 
(a) There is a need to organise visit to slum because slum dwellers should be educated about importance of hygienic conditions, for which there should be proper garbage disposal sites. Awareness should be spread about importance of good health, and they should consume fresh food, keep their surrounding clean. Such visits are required because inspite of providing various facilities, they have very poor sanitation, for example, they defecate in open and use same source of water for washing, bathing, cleaning, drinking etc.
(b) Various steps that should be undertaken for a healthy life of slum dwellers are:
(i) There should be proper toilets and no defecation in open.
(ii) Drains should be regularly cleaned to avoid stagnation of water and choking.
(iii) Overcrowding should be avoided.
(iv) Breeding grounds of mosquitoes should be destroyed to check spread of diseases.

Question. Since October 02, 2014 “Swachh Bharat Abhiyan” has been launched in our country.
(a) Write your views on this initiative giving justification.
(b) As a biologist name two problems that you may face while implementation of the programme in your locality.
(c) Suggest two remedial methods to overcome these problems.
Answer. (a) Mahatma Gandhi said “ Sanitation is more important than Independence.” Our country has a massive problem of open defecation. More than 72 percent of rural people in India respond to their nature’s call behind bushes, in fields or on roadsides. This has led to various other problems like untimely deaths of children, spread of infections and diseases. Nearly 55 percent of population has no access to toilets. Even in areas, where there are toilets in rural India there are no running water facilities available. Slum dwellers in cities have no access to running water supply and also toilets.
India will definitely be a clean country in coming years provided the government and the people participate in this Swachh Bharat Mission in a holistic manner. Swachh Bharat focusses on access to piped water, well-functioning drainage, sewage and solid waste management in all cities and villages, elimination of ponds in which stagnant water collects and serves as host to bacteria and mosquitoes.
Initiation of “Swachh Bharat Abhiyan” is an essential step for our country. It is not only the government who can make it a success, but people’s participation is of utmost importance.
(b) Implementation of this movement is not an easy task. Volunteers have to face various problems such as:
(i) It is very dificult to change the mindset of people, not to spit on roads, stair case etc.
(ii) Many people living even in good societies do have habit of keeping their garbage in open areas, which get spilled by animals (dogs, cats), thus polluting the colony.
(c) These problems can be overcome by implementing strict measures. (i) We can have committee of few members and whenever anyone spitting, throwing garbage on roads or urinating in open is spotted should be punished. (ii) We should keep sweepers on monthly wages for regular cleaning of roads. 

Agro-chemicals and their Effects

Short Answer Type Questions

Question. Why should the spraying of DDT as an insecticide on vegetable crops be banned? Explain. 
Answer. Spraying of DDT on vegetable crops should be banned because DDT is heavy metal and persistent pesticides passes into food chain and increases in amount per unit weight of organisms with the rise in trophic level due to their accumulation in fat. With agricultural run off, it enters into water body and harms aquatic life. Regular DDT spray for a few years, resulted in drastic decline in the population of fish eating birds. There was 1000 times increase in concentration of DDT in phytoplankton as compared to water, in zooplankton as compared to phytoplankton, in different fish as compared to zooplankton and more DDT in fish eating birds as compared to fish. Higher amounts of pesticide disturb calcium metabolism of birds resulting in thinning of egg shells and their premature breaking that kills the embryos. Other disorders due to DDT can be cerebral haemorrhage, softening of brain, liver cirrhosis, hypertension and malfunctioning of sex hormones. 

Radioactive Wastes

Very Short Answer Type Questions

Question. In spite of being non-polluting, why are there great apprehension in using nuclear energy for generating electricity?
Answer. Nuclear energy is not used for generating electricity because various radioactive pollutants damage white blood corpuscles, bone marrow, spleen, lymph nodes and may cause tumours, skin cancer, sterility etc. Even dairy animals may get highly contaminated by radioactive pollutants. 

Greenhouse Effect and Global Warming

Very Short Answer Type Questions

Question. Name the two gases contributing maximum to the greenhouse effect. 
Answer.CO₂ – 60% warming effect
CH₄ – 20% warming effect

Question. Name the greenhouse gases that contribute to global warming. 
Answer.Carbon dioxide, methane, chlorofluorocarbons and nitrous oxide.

Question. How is snow-blindness caused in humans?
Answer. Snow-blindness is inflammation of cornea due to absorption of UV-B radiations. It occurs due to depletion of ozone layer which increases amount of UV-B radiations reaching the earth.

Short Answer Type Questions

Question. Chlorofluorocarbons (CFCs) are widely used as refrigerants. Then why it is suggested to reduce its emission as far as possible? Explain.
Answer. Chlorofluorocarbons (CFCs) are greenhouse gases which contribute to 14% of global warming. CFCs cause ozone hole. In the stratosphere, chlorofluorocarbon is degraded in the presence of UV- radiation, releasing Cl atoms. Cl acts as catalyst in the degradation of ozone releasing molecular oxygen.

Question. The figure below shows the relative contribution of four greenhouse gases to global warming :

(a) Identify the gases A and C.
(b) Why are these four gases called the greenhouse gases?
 Answer.(a) A – CO₂ (60%)
B – CH₄ (20%)
C – CFCs (14%)
D – N₂O (6%)
(b) These four gases are called greenhouse gases, as these are transparent to solar radiations but retain and partially reflect back long wave heat radiations.These gases keep the earth warm and hospitable.

Question. How does global warming pose a threat to the coastal areas of the Earth? Explain. 
Answer. The global warming will raise the sea level due to melting of glaciers. A rise of even half a meter in sea level will be disastrous as thousands of islands and several important cities of the world and coastal areas will be submerged.

Short Answer Type Questions

Question. Describe greenhouse effect and list two greenhouse gases.
Answer. Greenhouse effect is the progressive, gradual warming of the earth’s atmosphere caused by the insulating effect of carbon dioxide and other greenhouse gases that have proportionately increased in the atmosphere. The greenhouse effect disturbs the way the earth’s climate maintains the balance between incoming and outgoing energy by allowing short-wave radiations from the sun to penetrate through to warm the earth, but preventing the resulting long-wave infrared radiations from escaping back into the atmosphere. There is concern that increasing concentration of greenhouse gases, including carbon dioxide, methane, and man made chlorofluorocarbons, may enhance the greenhouse effect and cause global warming.

Question. Explain the causes of global warming. Why is it a warning to mankind?
Answer. The main causes of global warming are :
(i) Deforestation
(ii) Increase in the use of CFCs.
(iii) Burning of fossil fuels
(iv) Increase in the use of nitrogen fertilisers. 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) Changes in the environment results in odd weather and climate changes, e.g., El Nino effect.
(iii) Many tree species and others which are sensitive to temperature will die out resulting in conversion of forests into scrub vegetation.
(iv) Small temperature rise may increase crop productivity in temperate areas but higher temperature rise will be detrimental.

Long Answer Type Questions

Question. (a) What is El Nino effect? Explain how it accounts for biodiversity loss.
(b) Explain any three measures that you as an individual would take, to reduce environmental pollution.
Answer. (a) EL Nino effect can be described as the warming of sea surface temperatures in the Pacific Ocean along the equator at irregular intervals. It influences weather patterns across the globe. It results in increasing the atmospheric temperature which results in global warming. This leads to rise in sea level and thus causing the biodiversity loss due to floods and also drought at some places due to very high temperature.
(b) Three measures to reduce environmental pollution are:
(i) By using unleaded petrol and diesel with reduced sulphur content.
(ii) By planting more trees.
(iii) By using television and loudspeakers at low volume.

Ozone Depletion in the Stratosphere

Very Short Answer Type Questions

Question. Write the unit used for measuring ozone thickness.
Answer.Dobson Unit (D.U).

Question. Mention two harmful effects of UV-B exposure on human eye.
Answer.UV-B exposure on human eye causes inflammation of cornea and cataract.

Question. State the purpose of signing the Montreal Protocol.
Answer. Industrialised countries signed Montreal Protocol to limit the production of chlorofluorocarbons to half to reduce depletion of ozone layer.

Question. Mention the causes of thinning of ozone layer.
Answer. Thinning of ozone layer is due to various ozone depleting substances such as:
(i) CFCs used in air conditioners and refrigerators.
(ii) Nitrogen oxides, sulphur dioxide, carbon tetrachloride etc., released by jets flying in stratosphere depletes ozone.

Question. Where is good ozone present? Why is it so called?
Answer. Good ozone is present in stratosphere. It is so called because it functions as shield for living organisms against strong harmful UV radiations from the sun.

Short Answer Type Questions

Question.

(a) What are the after effects of the degradation of ozone?
(b) How does it affect human health?
Answer. (a) Degradation of ozone will lead to higher mortality of young ones of animals, high number of mutations, inhibition of photosynthesis, decrease in the productivity of aquatic and terrestrial systems, global warming and disturbance in aquatic and terrestrial food chains.
(b) It severely affects human health. Cornea absorbs UV-B radiations and becomes inflamed called “snow blindness” cataract.
UV-B radiations can also damage skin cells, cause ageing of skin and skin cancer, increased incidence of herpes and deficient functioning of immune system.

Question. Explain the relationship between CFCs and ozone in the stratosphere.
Answer. Maximum ozone depleting potential or ODP is of chlorofluorocarbon due to release of active chlorine (Cl,ClO) by it. Active chlorine gets perched over atmospheric ice crystals and remains functional for a long time. A single chlorine atom converts 1 lakh molecules of ozone into oxygen.

Question. (a) State the cause of depletion of ozone layer.
(b) Specify any two ill-effects that it can cause in the human body.
Answer. (a) Depletion of ozone layer is due to reaction of ozone depleting substances (ODS) with ozone present in the stratosphere. The major ODS are chlorofluorocarbons (14% of total depletion), nitrogen oxides (3.5% depletion), sulphur dioxide, halon, carbon tetrachloride, methyl chloroform, chlorine, etc. Many of these are being released by jets flying in the stratosphere and rockets being fired into space. Maximum ozone depleting potential or ODP is of chlorofluorocarbon (used in ACs and refrigerators) due to release of active chlorine (Cl, ClO) by it. Active chlorine gets perched over atmospheric ice crystals and remains functional for a long time. A single chlorine atom converts 1 lakh molecules of ozone into oxygen.
(b) (b) It severely affects human health. Cornea absorbs UV-B radiations and becomes inflamed called “snow blindness” cataract.
UV-B radiations can also damage skin cells, cause ageing of skin and skin cancer, increased incidence of herpes and deficient functioning of immune system.

Short Answer Type Questions

Question. How is ozone formed in the stratosphere? Why is it called ‘good ozone’? CFCs contribute to ozone-hole formation. Explain. 
Answer. Ozone in stratosphere is formed by action of UV radiations on molecular oxygen.

It is called good ozone as ozonosphere acts as shield against strong UV radiations. CFCs discharged in the lower part of the atmosphere move upward and reach stratosphere. In the stratosphere, UV radiations act on CFCs and release Cl atoms. Cl atoms act as catalyst and degrade the ozone into molecular oxygen. Since Cl atoms are not consumed, whatever CFCs are added to the stratosphere, they have a permanent and continuing effect on ozone levels which may result in ozone hole formation.

Question. Explain greenhouse effect and depletion of ozone layer with reference to global warming.
Answer. Increase in concentration of greenhouse gases enhance greenhouse effect and leads to global warming which has resulted in rise of atmospheric temperature and due to this there will be melting of polar ice caps and mountain snow caps (e.g., Himalayan snow caps) which will raise sea level. The other effects of global warming include warming of troposphere accompanied by cooling of the upper strata of atmosphere. Cooling in the stratosphere will tend to increase the size of ozone holes which ultimately leads to ozone layer depletion.
Ozone depletion contributes in the thinning of ozone layer which increases the UV radiations reaching the earth. UV radiations inhibit photosynthesis and decreased photosynthetic activity will increase CO₂ concentration of the atmosphere resulting in global warming.

Question. What is the ozone shield and why is it important? Name the gases that cause stratospheric ozone depletion. 
Answer. 
Ozone shield is the region of stratosphere, where ozone is present in high concentration. It is called ozone shield because it protects the living beings from harmful effects of ultraviolet radiations. Damage to ozone shield results in impairment of photosynthetic machinery in plants which increase CO₂ concentration and results in global warming and skin cancer, cataract in humans.
The two gases that can cause damage to ozone shield are chlorofluorocarbons (CFCs) and methane (CH4).

Long Answer Type Questions

Question. (a) Why is the ozone layer required in the stratosphere? How does it get degraded? Explain. 
(b) Why is the ozone depletion a threat to mankind?
Answer. (a)  Good ozone is present in stratosphere. It is so called because it functions as shield for living organisms against strong harmful UV radiations from the sun.
Depletion of ozone layer is due to reaction of ozone depleting substances (ODS) with ozone present in the stratosphere. The major ODS are chlorofluorocarbons (14% of total depletion), nitrogen oxides (3.5% depletion), sulphur dioxide, halon, carbon tetrachloride, methyl chloroform, chlorine, etc. Many of these are being released by jets flying in the stratosphere and rockets being fired into space. Maximum ozone depleting potential or ODP is of chlorofluorocarbon (used in ACs and refrigerators) due to release of active chlorine (Cl, ClO) by it. Active chlorine gets perched over atmospheric ice crystals and remains functional for a long time. A single chlorine atom converts 1 lakh molecules of ozone into oxygen.
(b) Ozone depletion is a threat to mankind as it leads to thinning of ozone layer which results in the harmful UV radiations reaching the earth. The various effects of ozone depletion are :
– UV radiations inhibit photosynthesis which results in high CO₂ concentration of the atmosphere resulting in global warming. Due to this there will be rise in temperature resulting in melting of glaciers which will raise sea level due to thermal expansion of sea water leading to floods etc.
– Cornea absorbs UV-B radiations and becomes inflamed called “snow blindness” cataract. It leads to diminishing of eye sight, photoburning and later permanent damage to cornea that results in actual cataract.
– UV-B radiations damage skin cells, cause ageing of skin and skin cancer.
– There is increased incidence of herpes and deficient functioning of immune system.

Degradation by Improper Resource Utilisation and Maintenance

Very Short Answer Type Questions

Question. How have human activities caused desertification? Explain.
Answer. Loss of soil productivity by erosion of top soil results in the desert formation. Deserts are spreading in all continents, destroying the fertile land. Various human activities that cause desertification are:
(i) Human establishment : Forest areas have been cleared for building more residential complexes and industrial townships for ever increasing human population.
(ii) Overgrazing : The livestock graze in forest transpiring seedlings and cause soil compaction. This reduces water storing capacity and increases run off.
(iii) Requirement of wood for timber and paper industry resulted in clearing of forest land which leads to soil erosion resulting in the desert formation.

Deforestation

Very Short Answer Type Questions

Question. How does Jhum cultivation promote deforestation? 
Answer. In Jhum cultivation, or slash and burn agriculture, the farmers cut down the trees of the forest and burn the plant remains. Ash is mixed with soil and crops are sown in the cleared land. The land is used for two-three years without manuring, which results in nutrient depletion, reduced moisture retention and increased soil erosion resulting in deforestation.

Short Answer Type Questions

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. In India, 30% of the land was under forest cover at the beginning of the twentieth century. However, it has been reduced to 19.4% by the year 1999. National Forest Policy (1988) recommends an optimum 33% forest area for the plains and at least 67% for the hills. However, at present, it is much less than the recommended optimum figures.

Question. What is joint forest management? How can it help in conservation of forests? 
Answer. Realising the importance of participation by local communities, the Government of India in 1980s has introduced concept of Joint Forest Management (JFM) so as to work in close association with the local communities for protecting and managing forests. For such cooperation, the communities in return get benefits of various forest products (e.g., fruits, gum, rubber, medicine etc.). In this way, forests can be conserved in a sustainable manner.

Short Answer Type Questions

Question. What is agroforestry? How do shifting cultivation and taungya system of cultivation contribute to it? What is the difference between these two systems?
Answer. Agroforestry is plantation of multipurpose trees/shrubs/horticulture plants/grasses alongwith crops over agricultural land for stabilising soil, meeting the needs of fodder, fruit and timber of the community. Woody plants cover the land partially as they are grown in combination of herbaceous crops either at the same time or in time sequences. It adds to the income of farmers, stabilises soil and acts as wind break. In taungya system, agricultural crops are grown in between rows of planted trees like Sal and Teak. Jhum or shifting cultivation is a traditional system of agroforestry which allows regrowth of forests after clearing and cultivation in an area for a few years. The major difference between these two systems can be that in jhum cultivation system a part of forest is cleared for further cultivation while in taungya system, agricultural crops can be planted in between the rows of trees e.g., teak, sal, etc. without cutting the trees.

Question. Enumerate the consequences of deforestation.
Answer. The consequences of deforestation are as follows:
(i) Change in climate – Deforestation results in reduced rainfall, increased drought, hotter summers and colder winters.
(ii) Soil erosion – Soil is exposed to insolation, dries up and gets eroded by wind and water. It is estimated that 6000 million tons of top soil is lost annually in India due to water erosion in the absence of forest cover.
(iii) Drought – Deforestation negatively affects water cycle causing reduced precipitation. It increases the occurrence of drought.
(iv) Loss of biodiversity and germplasm.
(v) Global warming – Deforestation increases atmospheric CO₂ content by releasing carbon stored in organic matter and reduced primary productivity.