CBSE Class 12 Biology Environmental Issues Question Bank

 

Very Short Answer Questions

Question. Domestic sewage contains certain substances or salts which are difficult to remove. Name any four of them.
Answer. Nitrate, phosphate, metal ions and organic compound.

Question. Why does ozone hole form in spring and not in winter? 
Answer. Sunlight is necessary for ozone degradation and it is available only during spring.

Question. Eutrophication is the natural aging of a lake; mention any other feature which defines this term. 
Answer. —Depletion of dissolved oxygen in water
—Nutrient enrichment (Any one)

Question. Mention the effect of global warming on the geographical distribution of stenothermals like amphibians. 
Answer. Due to global warming, stenothermals would either migrate or die due to change in the temperature.

Question. BOD of two samples of water A and 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. Mention the effect of UV rays on DNA and proteins in living organisms. 
Answer. The high energy of UV rays breaks the chemical bonds within DNA and protein molecules.

Question. Excessive nutrients in a fresh water body cause fish mortality. Give two reasons.
Answer. Excessive nutrients result in excessive algal growth or eutrophication in the water body. Thus,
the water quality becomes poor as the oxygen level decreases.

Question. Which of the following is not a greenhouse gas? CO2, CH4, O2, CFCs.
Answer. O2.

Question. Why is the use of unleaded petrol recommended for motor vehicles equipped with catalytic converters? 
OR
Why is it desirable to use unleaded petrol in vehicles fitted with catalytic converters?
Answer. Lead in petrol inactivates the catalysts (platinum, palladium and rhodium) which convert harmful pollutants (CO, unburnt hydrocarbons, nitric oxide) to lesser harmful pollutants (CO2, H2O, N2).

Short Answer Questions

Question. (a) Name the green house gases that cause global warming.
(b) Which of them has caused ozone hole and how?
Answer. (a) CO2, CH4, N2O, chlorofluorocarbons or CFCs
(b) Ozone degradation has increased due to chlorofluorocarbons (CFCs). CFCs are refrigerants which react with UV in stratosphere to release chloride atoms. Chloride atoms act as catalyst to degrade ozone and release molecular oxygen. CFCs have permanent and continued effect as chloride atoms are not consumed.

Question. Explain giving reasons the cause of appearance of peaks ‘a’ and ‘b’ in the graph shown below. (Img 570)

Answer. ‘a’–High BOD due to sewage discharge.
‘b’–Increase in dissolved oxygen due to sewage decomposition.
Micro-organisms involved in biodegradation of organic matter consume a lot of oxygen, therefore,there is a sharp decline in dissolved oxygen. When the sewage is completely degraded, oxygen concentration again increases.

Question. A crane had DDT level at 5 ppm in its body. What would happen to the population of such birds? Explain giving reasons.
OR
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 were 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. DDT being a toxic substance gets accumulated in the organism and passes on to the next higher trophic level because it cannot be metabolised or excreted. Thus, concentration of DDT has increased in the birds in the given case. The high concentration of DDT disturbs the calcium metabolism in birds, causes thinning of eggshells, their premature breaking and eventually causes a decline in the bird population. The phenomenon is called biomagnification.

Question. How have human activities caused desertification? Explain. 
Answer. Human activities like over-cultivation, unrestricted grazing, deforestation and poor irrigation practices result in arid patches of land. The fertile top soil that may take centuries to develop is eroded due to these activities. When large barren patches extend and meet over time, a desert is created. Increased urbanisation is also one of the causes of desertification.

Question.  What measures, as an individual, you would take to reduce environmental pollution?
Answer. I will take following measures to reduce environmental pollution:
(i) Use of renewable energy resources.
(ii) Use of television and other instruments, at low pitch.
(iii) Minimum use of fossil fuel.
(iv) No tobacco smoking.
(v) Planting more trees.

Question.  List all the wastes that you generate, at home, school or during your trips to other places, could you very easily reduce? Which would be difficult or rather impossible to reduce?
Answer. Wastes are used up, unwanted and discarded materials which have to be disposed off.
(i) Wastes generated at home include kitchen waste, food left-overs, old and torn clothes, paper,polythene bags, plastic bags, carry bags, broken glass, carton boxes, tissue papers, etc.
(ii) Wastes generated at school include pens, papers, chalk, plastic envelopes, polythene, food wrappers, waste food, etc.
(iii) Wastes generated during trips include food wrappers, waste papers, polythene, disposable plates, spoons, cups, discarded food, etc.
Yes, we can reduce most of the wastes by its judicious use. Biodegradable wastes include all articles of organic origin, i.e., food wastes, waste paper, wood, leather articles and disposable articles which will be broken down by micro-organisms. Non-biodegradable wastes can be recycled and often taken away by rag-pickers. It is difficult to reduce non-biodegradable wastes.

Question. Ornithologists observed decline in the bird population in an area near a lake after the setting of an industrial unit in the same area. Explain the cause responsible for the decline observed.
Answer. Harmful wastes from the industrial unit must have entered the trophic levels of food chain causing biomagnification. It must have accumulated in the birds as it can neither be metabolised nor be excreted. High concentration of harmful chemical may disturb calcium metabolism in birds causing thinning of the egg shells and their premature breaking, ultimately causing decline in bird populations.

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

Answer. When sewage is discharged into the river, the oxygen concentration declines sharply because a large amount of oxygen is consumed by aerobic microorganisms in river to decompose the organic matter in river. When the amount of organic matter reduces, the amount of dissolved oxygen again increases.

Question. “Determination of Biological Oxygen Demand (BOD) can help in suggesting the quality of a water body.” Explain. 
Answer. High BOD of a water body indicates growth of more number of micro-organisms in water. This results in bad quality of water. Bad water quality will lead to death of aquatic creatures and hence more polluting potential. Whereas lower BOD of water body indicates less number of microorganisms in water. There is good quality of water in which aquatic life flourishes and there is less polluting potential.
The amount of oxygen required for microbial breakdown of biodegradable organic matter is called BOD.

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. This results in reduced microbial decomposition. When there is no decomposition,oxygen utilisation is reduced and there is more Dissolved Oxygen (DO) available. Thus, clean water-organisms reappear.

Question. Suppose sewage water is disposed off in the river. What will be its effect on BOD and dissolved oxygen?
OR
Sewage discharge into clean water body leads to increased fish mortality. Explain.
Answer. Discharge of sewage water into a river will increase nutrients and thereby promotes algal growth. This will result in rise of BOD (Biochemical Oxygen Demand) as decomposers will consume more dissolved oxygen in river. If sewage quantity is large, the whole of the dissolved oxygen will be consumed leaving nothing for respiration of fishes and other aquatic organisms. This increases the mortality rate of aquatic creatures.

Long Answer Questions

Question. With the help of a flow chart, show the phenomenon of biomagnification of DDT in an aquatic food chain.
Answer. 

Question. Explain accelerated eutrophication. Mention any two consequences of this phenomenon.
Answer. Accelerated eutrophication is nutrient enrichment of water bodies due to human activities like passage of sewage.
Consequences are:
(i) Large amount of nutrients in water causes excessive growth of planktonic algae (called algal bloom) which impart characteristic colour to water bodies.
(ii) Depletion of oxygen content of water leading to the death of the aquatic organisms.

Question. With the help of a flow-chart exhibit the events of eutrophication. 
Answer. 

Question. Eutrophication is the natural aging of a lake. Explain.
Answer. Eutrophication is the natural aging of a lake by biological enrichment of its water. In a young lake, the water being cold and clear, does not support much life. But 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 begins to develop and organic remains begin to be deposited on the lake’s bottom. Over the centuries, as silt and organic debris pile up, the lake grows shallower and warmer. Now, the warm water organisms replace those that live in a cold environment. Marsh plants take root in the shallows and begin to fill in the original lake basin. Eventually, the lake develops large masses of floating plants (bog), finally converting into land.

Question. What is eutrophication? How does a lake undergo accelerated eutrophication? 
Answer. Eutrophication
• It is defined as the natural aging of a lake by biological enrichment of its water.
• Water in a young lake is cold and clear to support life.
• With time, it is enriched with nutrients like nitrogen and phosphorus by streams draining into it.
• This encourages growth of aquatic life—plant and animal life.
• Organic remains deposit at the bottom of the lake and with time makes the water warmer and shallower. 
• 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.

Question. Explain the cause of algal bloom in a water body. How does it affect an ecosystem?
OR
How does algal bloom destroy the quality of a fresh water body? Explain.
Answer. Domestic sewage and industrial effluents contains nutrients like nitrogen and phosphorus which favour the excessive growth of planktonic (free-floating) algae.
Its harmful effects cause:
(i) sharp decline in dissolved oxygen content in the water.
(ii) deterioration of water quality and causes mortality of aquatic life forms.
(iii) distinct odour from the water bodies.

Question. Discuss briefly the following:
(a) Greenhouse gases (b) Catalytic converter (c) Ultraviolet B
Answer. (a) Greenhouse gases: The gases which allow solar radiations to pass through them but retain and partially reflect back radiation of longer wavelength are called greenhouse gases, e.g., CO2, NO2, CH4, etc. These gases are required to keep earth warm and hospitable. They prevent a substantial part of long wave radiations emitted by earth to escape into space.
Rather greenhouse gases radiate a part of this energy back to the earth.
(b) Catalytic converter: Refer to Basic Concepts Point 2 (iv)(c).
(c) Ultraviolet B: These are UV radiations with wavelength ranging between 280–320 nm. They are harmful radiations that penetrate through the ozone hole to reach the earth. Ozone shield is thinning over the equator. UV-B radiation causes cataract and skin cancer in human beings.
High levels of UV-B radiation damages DNA of an individual.

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. Explain any three measures which will control vehicular air pollution in Indian cities.
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. 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 efficient 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.

Question. Excessive nutrients in a freshwater body cause Thsh 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. Write the name of the organism that is referred to as the ‘Terror of Bengal’. 
Answer. Eichhornia crassipes (water hyacinth).

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 effiuents from the industries and homes such as sewage, agriculture wastes, etc. have radically accelerated this ageing process. This phenomenon is called accelerated eutrophication.

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

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 is the use of unleaded petrol recommended for motor vehicles equipped with catalytic converters?
Answer. 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. List two gaseous products that are produced when exhaust of an automobile passes though a catalytic converter. 
Answer. Carbon monoxide and nitrogen oxide.

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. 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 efficiently, does not produce much pollution, cannot be siphoned off by thieves and it cannot be adulterated like petrol and diesel.

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. State the function of a catalytic converter in an automobile.
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. How does an electrostatic precipitator work to remove particulate pollutants released from the thermal power plants? 
Answer. Electrostatic precipitator is the most efficient 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. How do automobile fiitted 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.

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. (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 efficient 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. 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. 

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 the changes that can be observed in the characteristics of river water when sewage is discharged into it and a few weeks after 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. 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. (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 efficient 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. 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 difficult 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.

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. 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 effiuents 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. ‘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. 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. 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 effiuents, 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. Why should the velocity of air between the plates of an electrostatic precipitator be low?
Answer. To allow the dust to fall.

Question. PM2.5 is responsible for causing greatest harm to human health. What is it? How is it harmful?
Answer. PM2.5 stands for particulate matter of size 2.5 micrometres or less in diameter. It’s 1m responsible for causing greatest harm to human health as it can be inhaled deepn into lungs and cause breathing problems.

Question. What is the noise level that can cause permanent impairment of hearing ability of human beings?
Answer. 150 dB or more

Question. Why was the Montreal Protocol signed?
Answer. To control emission of ozone depleting substances

Question. Jhum cultivation has been in practice from earlier days, but its considered more problematic these days. Why?
Answer. Enough time gap is not being given for the natural process of recovery of land 1m
from the effect of cultivation

Question. A radiation causes ageing of skin, skin cancer, and inflammation of cornea called snow blindness. It also damages DNA. Name the radiation.
Answer. Ultraviolet B rays (UV-B rays)

Question. Landfills are not much a solution for getting rid of solid wastes. Why?
Answer. Landfill sites are getting filled very fast due to large amount of garbage generation. 
Also underground water resources may get polluted due to seepage of chemicals

Question. Electrostatic precipitator can remove over 99% particulate matter present in exhaust from a thermal power plant. How?
Answer. Electrode wire at thousand volts, produce corona to release electrons,electrons attach to dust particules giving them net negative charge, charged dust particules
attracted/collected by collecting plates which are grounded

Question. Why is a scrubber used? Which spray is used on exhaust gases passing through a scrubber?
Answer. To remove gases like sulphur dioxide. Spray of water or lime is used

Question. There is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. Why? What are its adverse effects?
Answer. Following discharge of sewage into river, micro organisms involved in biodegradation of organic matter present in sewage consume more oxygen.This cause mortality of fish and other aquatic creature

Question. Catalytic converters use expensive metals as catalysts.
(a) Name the metals generally used.
(b) What precaution should be observed while using catalytic converter?
Answer. (a) Catalysts : platinum - palladium and Rhodium
(b) Motor vehicles equipped with catalytic converters should use unleaded petrol as lead inactivates the catalysts.

Question. What are e-wastes? Why are they creating more problems in developing countries in comparison to developed countries?
Answer. a) Irrepairable computers and other electronic wastes. 
(b) Recycling in developing countries involves manual participation thus exposing workers to toxic substances. In developed countries its mechanised so less dangerous

Question. Water logging and salinity are some of the problems that have come in the wake of Green revolution. How does water logging create problems of salinity?
Answer. Water logging draws salt to surface of soil. Salt deposited on land surface 2m as a thin crust or at the roots of the plants

Question. What is the relationship between BOD, micro-organisms and amount of biodegradable matter?
Answer. Increase in amount of biodegradable matter leads to rapid multiplication  of micro organisms to degrade it, thereby increasing BOD level of the water body.

Question. Deforestation is creating a lot of problems in the environment. List the consequences of deforestation.
Answer. Enhanced CO₂ concentration in atmosphere, Loss of biodiversity ,Soil erosion Desertification ,Disturbed hydrological cycles.

Question. Enlist four harmful effects caused to the humans living in areas having polluted air. Suggest two measures to reduce air pollution.
Answer. Breathing problems, irritation and inflammation, Damage to lungs, Premature death. Reduce emission from automobile exhaust , Growing more trees

Question. People have been actively participating in the efforts for the conservation of forests.
(i) Name the award instituted in respect of Amrita Devi to promote such fforts.
(ii) Name the movement launched to protect the trees by hugging them.
(iii) Name the step Government of India has undertaken in 1980.s to work closely with the local communities for protecting and managing forests.
Answer. (i) Amrita Devi Bishnoi Wildlife Protection Award. (ii) Chipko movement
(iii) Joint Forest Management (JFM).

Question. Pollutant released due to human activities (like effluents from industries and homes) can radically accelerate the ageing process of the water body.
(a) Explain how does this process occurs during natural ageing of lake.
(b) Give the term used for accelerated ageing of water bodies. Also give the term used for the natural ageing of lake.
Answer. a) The phenomeon is eutrophication. More nutrients in water, aquatic life increases organic remains deposited on lake bottom, lake grows shallower and warmer, gradually transforms into land due to deposition of silt and organic debris.
(b) Cultural or Accelerated eutrophication ,Natural ageing is Eutrophication

Question. In Arcata, the town’s people have created an integrated waste water treatment process within a natural system. A citizen group called FOAM helps in upkeep of this project.
(a) What are the main steps in waste water management done in this way?
(b) Ecosan. in Kerala and Sri Lanka is also an initiative for water conservation. How?
Answer. a) Conventional sedimentation, filtering and chlorine treatment. Absorption and  assimilation of pollutants by algae fungi and bacteria.
(b) Ecosan. derived from ecological sanitation. Handling human excreta using dry composting toilets. Its practical, hygienic and cost effective method.

Question. What are the contribution of Ahmed Khan in Bangalore and Ramesh Chandra Dagar in Sonipat?
Answer. a)Polyblend ,a fine powder of recycled modified plastic is mixed with bitumen &  used to lay roads. This increases bitumen water repellent properties & increase road life by a factor of three
b) Integrated organic farming is a cyclical, zero waste procedure, where waste from process are cycled in as nutrients for other process. He included bee keeping, dairy management, water harvesting composting and agriculture in s chain of processes.

Question. Since the use of polybags has become so rampant in our day to day life, it is impossible to go back to non-plastic era. Today, the plastic menace has spread from cities to small towns and village. They are “Garbage Forever”.
i) What are the harmful effects of using polybags?
ii) In your opinion, what steps should be taken to solve this problem?
Answer. (I) Non degradable, choke our sewage & drainage system, stray cattle eats it &  choke its digestive system
(II) Using paper,jute,cloth bags. Minimise the use voluntarily. Segregation of biodegradable & non-biodegradable material to safe disposal. Educating people on health risk, production of biodegradable plastic bags by mixing cellulose during their manufacturing.

Question. Nowadays, we see that people use CDs & DVDs for storing information, movies and songs.
i) Do you think these things create pollution?
ii) Which values are expressed, on the basis of information?
Answer. Yes, these contain heavy metals & toxic substances. As the technology is  changing these products are replaced by i pods, pen drives. They constitute e-waste.

 

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