Important Questions for CBSE Class 12 Biology Pollution, Solid and Radioactive Wastes

Environmental Issues Important Questions for CBSE Class 12 Biology Pollution, Solid and Radioactive Wastes

1.Pollution is an undesirable change’in the physical, chemical and biological characteristics of air, water, land and soil.

Pollutants are agents that cause undesirable change in the environment.
The Government of India has passed the Environment Protection Act, 1986 to protect and improve the quality of our environment (air, water and soil).

2.Air pollution occurs due to undesirable change in the physical, chemical and biological characteristics of air that exerts harmful effects on human beings.

(i) Causes of Air Pollution

Smoke stacks from thermal power plants, forest fires, volcanic eruptions, etc.
Garbage decomposition also releases unwanted gases in the air.
Excessive use of fossil fuels by automobiles and industries release particulate and air pollutants.
Use of leaded petrol.

(ii) Types of Air Pollutants

(iii) Harmful Effects of Air Pollution on Health

Carbon monoxide (CO) causes giddiness, headache, cardiovascular malfunction, asphyxia, etc.
Hydrogen sulphide (H₂S) causes nausea, eye and throat irritation.

Sulphur dioxide (S0₂) causes respiratory tract diseases like asthma, bronchitis, cancer, emphysema, etc.
Fine particulates released by industries cause breathing and respiratory problems, inflammation and damage to the lungs.
In plants reduced growth and yield and premature death occurs.

(iv) Control Methods of Air Pollution

There are several methods used for controlling air pollution in India.

These are:

(a) Electrostatic Precipitator (ESP) is an electrical device to remove particulate matter present in the exhaust of thermal power plant.

About 99% of particulate matter can be removed by ESP.
It has electrode wires and a stage of collecting plates.
Electrode wires are provided with an electric current of several thousand volts, which produces a corona that releases electrons.

These electrons get attach to the dust Electrostatic precipitator particles and give them negative charge within a small fraction of a second.

Collecting plates are grounded that attract the charged dust particles.
The velocity of air between the plates must be low enough to allow the dust to fall.

(b) Scrubber is used to remove harmful gases like sulphur dioxide from industrial exhaust.

The exhaust is passed through a spray of water or lime.
Water dissolves the gases and lime reacts with sulphur dioxide to form a precipitate of calcium sulphate and sulphide.
Drawbacks Recently, the dangers of particulate matter that are very small and cannot be removed by these precipitators has been found. According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) if inhaled can cause breathing and respiratory problems, irritation, damage to lungs and premature deaths.

(c) Catalytic convertors are fitted into automobiles for reducing emission of poisonous gases like N0₂ and CO.

They are made of expensive metals like platinum, palladium and rhodium as catalysts.
When exhaust passes through the catalytic convertor, nitric oxide splits into nitrogen and oxygen; carbon monoxide is oxidised into carbon dioxide and unburnt hydrocarbons get burnt completely into C0₂ and H₂0
Unleaded petrol should be used in motor vehicles fitted with catalytic convertor as leaded petrol inactivates the catalyst.

(v) Auto Fuel Policy of Government of India

Euro II norms stipulate that sulphur be controlled at 350 parts per million (ppm) in diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42% of the concerned fuel.
According to it, all automobiles have to meet the Euro III emission specification in eleven Indian cities by 1 April, 2005.
The same eleven cities have to meet the Euro IV norms by 1 April, 2010.
The rest of the country will have Euro III emission norm compliant automobiles and fuels by 2010.
By all these efforts, a substantial fall in C0₂ and S0₂ level has been found in Delhi between 1997 and 2005.

3. Noise pollution is undesirable high level of sound. In India, the Air (Prevention and Control of Pollution) Act came into force in 1881, but was amended in 1987 to includes noise as art air pollutant.

Noise measurement Sound is expressed in decibels (dB). A sound of over 115 dB is very harmful for ears. Prolonged exposure to noise level above 80 dB leads to perma nent hearing loss.

(i) Causes are

(a) Use of loudspeakers and music systems. (b) Jet planes and rockets take-off.

(ii) Harmful effects are sleeplessness, stress, increased heartbeat, breathing problems, damage to ear drums and impaired hearing ability.

(iii) Control Methods

By applying sound-absorbent materials or by muffling noise in industrial units.
Delimitation of horn-free zones around hospitals and schools.
Strict laws for permissible sound levels of crackers and loudspeakers should be followed.
Loudspeakers should be played up to a fixed time only.

4. Water pollution is any undesirable change in the physical, chemical or biological properties of water that may affect the human beings and aquatic species.

(i) The Government of India has passed the Water (Prevention and Control of Pollution) Act, 1974 to safeguard our water resources.

(ii) Sources of Water Pollution

(a) Domestic sewage includes everything that comes from residential area to common public sewage system. A mere 0.1% impurities make domestic sewage unfit for human use.

Composition of domestic sewage

Suspended solids, e.g. sand, silt and clay.
Colloidal material, e.g. faecal matter, bacteria, cloth and paper fibres.
Dissolved materials, e.g. nutrients (nitrate, ammonia, phosphate, sodium and calcium).
It mainly contains biodegradable organic wastes, which are readily decomposed with the help of decomposers.

(b) Industrial wastes are released by petroleum, paper manufacturing, metal extraction and processing units.

It contains heavy metals like mercury and many organic compounds.

(iii) Effects of Water Pollution

(a) Biological magnification can be defined as the increase in concentration of toxicants at successive trophic levels.

Mercury and DDT are well known for biological magnification.
Toxic materials cannot be metabolised or excreted. Therefore, they get accumulated in an organism and pass on to higher trophic levels.
DDT accumulates in birds and disturbs calcium metabolism, which results in thinning of egg shell. This results in decline of bird population.

(b) Eutrophication can be defined as the natural ageing of a lake by nutrient enrichment of its water.

Process of Eutrophication

Water in young lake is cold and clear to support life.
Gradually with time, it gets enriched with nutrients as nitrogen and phosphorus by streams draining in it.
Due to this, aquatic life (plants and animals) flourish in lake.
Organic remains deposit at the bottom of the lake and with time, water becomes warmer. Eventually, floating plants develop in the lake, finally converting it into land. This accelerated ageing of lakes due to sewage, agricultural and industrial wastes is called cultural or accelerated eutrophication

(c) Biochemical Oxygen Demand (BOD) is the amount of oxygen required for microbial breakdown of biodegradable organic matter. It is higher in polluted water and lesser in clean water.

(d) Algal bloom is excessive growth of planktonic (free-floating) algae in aquatic bodies.

In domestic sewage, nutrients like nitrogen and phosphorus favours the growth of algal bloom.
It causes fish mortality and deterioration of water quality.

Example, Excessive growth of water hyacinth (Eichhornia crassipes). It is the most problematic aquatic weed, also called Terror of Bengal.

It grows abundantly in eutrophic water bodies and imbalances water ecosystem.

(vi) A Case Study— Integrated Wastewater Management

(a) Wastewater including sewage can be treated in an integrated manner by utilising a mix of artificial and natural processes.

One such example is town of Areata situated along Northern coast of California. An integrated wastewater treatment process was developed with the help of biologists from Humboldt State University in this town.
The cleaning occurs in two steps:

— The conventional sedimention, filtrating and chlorine treatment is carried out.

The treated water still contain lots of heavy metals and other toxic pollutants.

– In second step, algae, fungi and bacteria are grown in marsh land through which water flowed. These life forms neutralise, absorb and assimilate the pollutants and purify the water naturally.

, • The marshes also constitute a sanctuary, with a high level of biodiversity.

(b) Ecosan toilets have been developed in areas of Kerala and Sri Lanka for ecological sanitation. The advantages of ecological sanitation are:

A practical, hygienic and efficient method of disposal.
Cost effective approach.
Human excreta can be recycled into natural fertiliser to reduce need of chemical fertiliser.

5. Solid wastes refer to everything that goes out in trash. The various types are:

(i) Municipal solid wastes contain wastes from homes, offices, schools, hospitals, etc., that are collected and disposed by the municipality, which generally consists of paper, leather, textile, rubber and glass, metals and plastic, etc.

(ii) Industrial wastes contain wastes like scraps, fly ash, etc., generated by industries.

(iii) Hospital wastes contain disinfectants and other harmful chemicals generated by hospitals.

(iv) Electronic wastes (e-wastes) are the damaged electronic goods and irreparable computers.

(a) Methods of Solid Waste Disposal

There are various methods of solid waste disposal. Some of them are:

Open burning involves burning of municipal waste in open dumps but the unburnt piled waste serves as breeding ground for rats and flies.
Sanitary landfills are areas where wastes are dumped in a depression or trench after compaction and covered with dirt. The problem is seepage of chemicals from these landfills can pollute underground water resources.
Rag-pickers and kabadiwallas collect and separate out wastes into reusable or recyclable categories.
Natural breakdown involves dumping biodegradable materials into deep pits for natural degradation.
Incineration is a method of hospital waste disposal.
E-Wastes
E-wastes are buried in landfills or in ~inerated.
About half of the e-wastes generated in the developed world are exported to developing countries, mainly to China, India and Pakistan, where metals like copper, iron, silicon, nickel and gold are recovered during recycling process.
Developed countries have specifically built facilities for recycling of e-wastes.
Recycling is only solution available for treating e-waste but caution should be taken to carry out process environment friendly.

(b) A Case Study — Remedy for Plastic Waste

A plastic sack manufacturer, Ahmad Khan from Bengaluru realised that plastic waste was a real problem. His company developed a fine powder, called polyblend of recycled modified plastic. ^; This mixture is mixed with the bitumen and used to lay roads.

It enhanced the bitumen’s water repellant properties and helped to increase road life by a factor of three.
Using this technique, by the year 2002, more than 40 kms of road in Bengaluru has already been laid.

6. Soil pollution is any undesirable change in soil profile affecting its productivity.

(i) Green revolution led to manifold increase in crop production by the use of inorganic fertilisers and pesticides.

(ii) Pesticides, herbicides, fungicides, etc., are being increasingly used afterwards which resulted in so’l pollution.

(iii) Causes of Soil Pollution

(a) Chemical seepage from industries.

(b) Excessive use of inorganic fertilisers, pesticides, etc.

(iv) Harmful Effects of Soil Pollution

Non-target organisms are killed in the soil.
Soil becomes unfertile.
Pesticides can result in biomagnification.

(vi) Control Methods

Strict ways should be adopted by the industries and other sources for waste disposal.
Use of organic farming It is a cyclical, zero-waste method, where waste products from one process are cycled in as nutrients for other processes, allowing maximum utilisation of resources and increasing the efficiency of production.

(vii) A Case Study— Organic Fanning

Ramesh Chandra Dagar, a farmer in Sonipat (Haryana) included bee-keeping, dairy management, water harvesting, composting and agriculture in a chain of processes.
This chain supports each other and allow an extremely economical and sustainable venture.
Chemical fertilisers are not required as cattle excreta is used as manure.
Crop waste is used for making compost, which is used as natural fertiliser or to generate natural gas, which is used for satisfying energy needs of farm.
To spread information and help the practice of integrated organic farming. Dagar has created the Haryana Kisan Welfare club, with current membership of 5000 farmers.

7. Radioactive wastes include nuclear waste, which is given off as radiation.

(i) Nuclear energy was initially considered as a non-polluting way for generating electricity initially.

(ii) Later, two serious inherent problems were realised. The first is accidental leakages as occurred in the Three Mile Island and Chernobyl, which proved that radioactive wastes are most potent pollutants. The second is safe disposal of radioactive wastes.

(iii) Harmful Effects

Radiations causes mutation at a very high rate.
At high doses, nuclear radiations are lethal.
At low doses, these cause disorders and diseases like cancer.

(vi) Disposal method of radioactive wastes involve pretreatment and storage in shielded containers and then burying at about 500m deep below the earth’s surface. However, this method of disposal is getting opposition from public.

Previous Years Examination Questions

1 Mark Questions

1.State the cause of accelerated eutrophication. [Delhi 2014]

Ans. Effluents from industries and domestic sewage and other human activities are the causes of accelerated eutrophication,

2.Inspite of being non-polluting, why are there great apprehensions in using nuclear energy for generating electricity? [Foreign 2014]

Ans.Despite being non-polluting, there are great apprehensions in using nuclear energy for generating electricity because of

(i) danger of accidental leakage.

(ii) lack of safe disposal methods of radioactive waste.

3.Why is the use of unleaded petrol recommended for motor vehicles equipped with catalytic convertors? [All India 2013,2012 Foreign 2010] or

Why are owners of motor vehicles equipped with catalytic convertors advised to use unleaded petrol? [Delhi 2009]

Ans.Lead found in petrol corrode the catalytic rods of platinum, rhodium which act as the catalyst in catalytic convertor and decreases its efficiency. Thus, unleaded petrol is recommended for motor vehicles equipped with catalytic convertors

4.Why is Eichhornia crassipes nick named as Terror of Bengal? [Delhi 2012]

Ans.The plant Eichhornia crassipes is nick named as the Terror of Bengal’ because it grows at an alarming rate and spreads on the surface of the water body. This cuts out light and also causes an increase in the oxygen demand. Thus, causing the death of fishes and other aquatic organisms,

5.How do algal blooms affect the life in water bodies? [All India 20113]

Ans.Algal blooms cause deterioration of the water quality. They reduce the dissolved oxygen content of water and cause mortality (death) of aquatic animals like fish. They also secrete chemicals, toxic to humans and many other animal

6.Eichhornia crassipes is an alien hydrophyte introduced in India. Mention the problems posed by this plant. [All India 2010c]

Ans. Eichhornia crassipes (water hyacinth) is the world’s most problematic aquatic weed. It grows abundantly in eutrophic water bodies and imbalances water ecosystem. It blocks the water, ways and growth of other organisms due to its excessive growth

7.Given below are a few impurities in Urban wastewater. Select two colloidal impurities : ammonia, faecal matter, silt, bacteria, calcium. [All India 2009c]

Ans. Faecal matter and bacteria are two colloidal impurities suspended in urban waste

8.Name the world’s most problematic aquatic weed. What is the nature of the waterbody in which the weeds grow abundantly? [Delhi 2008]

Ans. The world’s most problematic weed is Eichhornia crassipes (water hyacinth). In Eutropic water bodies, weeds grow abundantly

2 Marks Questions

9.Name two metals used in a catalytic convertor. How do they help in keeping the environment clean? [Delhi 2014c]

Ans.The two metals used in a catalytic convertor are platinum palladium and rhodium (any two).

The catalytic convertors fitted in automobiles reduce the emission of poisonous gases by converting the unburnt hydrocarbons into C0₂ and water, carbon monoxide to C0₂ and Nitric oxide (NO) to nitrogen, while the exhaust is passed through them.

10.’Fish mortality increases with influx of nutrients in a freshwater body’. Write two reasons. How will the influx of nutrients affect the BOD level of this waterbody? [All India 2014c]

Ans.Fish mortality increases with influx of nutrients in a freshwater body because

(i) Abundant nutrients encourage the growth of free floating algae and plants, thereby increasing organic matter.

(ii) With the increase in organic matter and its deposition, the water body becomes shallows and warmer. Further deteroriation of organic matter makes the environment toxic and unfit for survival of aquatic life, i.e. fishes.

The influx of nutrients increases the BOD level of water body, as the microbes flourishing in it consume up all the oxygen in degrading the organic matter. As the Biochemical Oxygen Demand (BOD) increases, the Dissolved Oxygen (DO) decreases, making the water body unfit for aquatic life

11.Explain how does the inflow of large amount of nutrients like phosphates and nitrates into the water body drastically affects the aquatic life there. Name the phenomenon responsible. [Delhi 2014c]

Ans. The inflow of large amounts of nutrients like nitrates and phosphates initially encourages growth of aquatic organisms, plants and animals. With time as the organic matter increases, debris along with silt piles up at bottom making the water body shallower and warmer. This leads to gradual appearance of floating and marshy plants and is eventually converted into lake. Hence, the aquatic life gets severely affected and disrupted.

This phenomenon is called eutrophication. It may be natural or artificial due to result of human activities.

12.How did Ahmad Khan, plastic sac manufacturer from Bengaluru, solve the ever-increasing problem of accumulating plastic waste? [All India 2012]

What is polyblend? Why did the plastic manufactures think of producing it? Write its usefulness? [All India 2011]

Ans.Ahmad Khan developed a fine powder called polyblend of recycled modified plastic. This mixture is mixed with the bitumen and used to lay roads. It enhanced the bitumen’s water repellant properties and helped to increase road life by a factor of three. By this way, the problems created by plastic waste was solved.

13.State the function of a catalytic convertor in an automobile. [All India 2011C]

Ans.Catalytic convertor are used for reducing emission of poisonous gases like N0₂ and CO. When exhaust emission passes through catalytic convertor, nitric oxide splits into nitrogen and oxygen, carbon monoxide is oxidised into carbon dioxide and unburnt hydrocarbons get burnt completely into C0₂and H₂0

14.Study the graph given below. Explain how oxygen concentration is affected in the river, when sewage is discharged into it? [Delhi 2011]

Ans. The graph shows the decrease in dissolved oxygen due to sewage decomposition. When sewage is discharged into river, microorganisms present in water helps in biodegradation of organic matter. They consume a lot of oxygen. Therefore, there is a sharp decline in dissolved oxygen. When the sewage is completely degraded, oxygen concentration again increases.

15.Study the given aquatic food chain. Answer the question that follow [Delhi 2010]

(i) Give reason, why there is a continuous increase in the DDT content in different trophic levels of the chain?

(ii) Name the phenomenon responsible for the increase in DDT content.

Ans.

(i) Continuous increase in DDT concentration is becuase of following reasons:

It cannot be metabolised.
It is not excreted, but it is passed on to next higher tropic level.

(ii) Biomagnification is the phenomenon responsible for increase in DDT content

16.How does an electrostatic precipitator work to remove particulate pollutants released from the thermal power plants? [Delhi 2010]

Ans. Electrostatic Precipitator (ESP) is an electric device to remove particulate matter present in the exhaust of thermal power plants. ESP has electrode wires and a stage of collecting plafes. Wires are provided with an electric current of several thousands volts, which produces a corona that releases electrons^) These electrons attach to dust particles, giving them a negative charge within a very small fraction of a second. Collecting plates are earthed, so that they attract charged dust particles. The velocity of air passing through plates is slow enough to allow the dust particles to fall on them.

17.Mention the major cause of air pollution in metro cities. Write any three ways, which it can be reduced. [All India 2010]

Ans.Major causes of air pollution are:

(i) Smoke from thermal power plants, forest fires, volcanic eruptions.

(ii) Use of unleaded petrol.

(iii) Excessive use of fossil fuels by automobiles and industries releasing particulate and air pollutants.

Three control methods are:

(i) Using electrostatic precipitators to remove particulate matter from exhaust of industries and thermal power plant.

(ii) Using scrubber to remove gases like so₂.

(iii) Use of catalytic convertors in automobiles for reducing emission of poisonous gases.

18. Mention how e-waste is produced and disposed off? Write the solution for its treatment. [All India 2010]

Ans. Electronic wastes (e-waste) include irrepairable electronic goods and computers. E-wastes can be buried in landfills or incinerated. Recycling is the only solution for the treatment of e-wastes.

19. Explain giving reasons the cause of appearance of peaks A and B in the graph shown below.

Ans. A -High BOD due to sewage discharge complete.

B-Increase in dissolved oxygen due to sewage decomposition.

Microorganisms 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.

20.Explain accelerated eutrophication. Mention any two consequences of this phenomenon. [Delhi 2009]

Ans.Accelerated eutrophication It is the phenomenon that accelerates the ageing process of a water body due to sewage, agricultural and industrial wastes.

Consequences

(i) The nitrates, phosphates that enter the water body stimulate the excess growth of algae and some plants. This causes unpleasant odour and scum formation.

(ii) Due to this, dissolved oxygen content of water decreases leading to death of aquatic organisms

21.A crane had DDT level as 5 ppm in its body. What would happen to the population of Such birds? Explain giving reasons. [Delhi 2009]

Ans. The high concentration of DDT (5 ppm) in cranes disturb their calcium metabolism, which causes thinning of egg shell and their premature breaking, thereby causing decline in bird population.

22.Explain the cause of algal bloom in a water body. How does it affect an ecosystem? [All India 2009]

Ans.Algal bloom is caused by excess the presence of nutrients (mainly nitrogen and phosphorus) in the water body. They cause

(i) Deterioration of water quality.

(ii) Fish mortality.

(iii) Toxic effect on aquatic animals and human beings.

23.How do automobiles fitted with catalytic convertors reduce air pollution? Suggest the best fuel for such vehicles. [Foreign 2009]

Ans.Catalytic convertor are used for reducing emission of poisonous gases like N0₂ and CO. When exhaust emission passes through catalytic convertor, nitric oxide splits into nitrogen and oxygen, carbon monoxide is oxidised into carbon dioxide and unburnt hydrocarbons get burnt completely into C0₂and H₂0

24.Thermal power plants are inevitable in an industrial and densely populated country like ours. What harm they do the environment? Also mention any precaution that could be taken to save our environment. [Delhi 2008]

Ans.Thermal power plants have smoke stacks, which release particulate and gaseous air pollutants in the environment. When these pollutants are inhaled. They cause

(i) Breathing and respiratory problems.

(ii) Irritation, inflammation and damage to lung alveoli.

(iii) Premature death.

Precautionary measure: By use of electrostatic precipitators, 99% of the particulate matter can be removed

25.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 are 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. [Ail India 2008]

Ans. DDT gets accumulated in the organisms and passes to next higher trophic level through food chain because it cannot be metabolised or excreted. Hence, concentration of DDT gets increased in birds. They disturb the calcium metabolism and causes thinning of egg shell and their premature breaking.

This eventually causes a decline in the bird population. This phenomenon is called biomagnification

26.Name any two sources of electronic wastes. Mention any one way each of its disposal in developing and developed countries. [Delhi 2008]

Ans. Sources of electronic wastes are irrepairable computers and other electronic goods.

Disposal methods of E-waste.

In developed countries E-wastes are buried in landfills or incinerated.

In developing countries Developed countries export e-wastes mainly to China, India and Pakistan. Here, metals like copper, iron, silicon, nickel and gold are recovered during recycling process. It involves manual participation

3 Marks Questions

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

Answer the questions based on the facts given above:

Name the organisms depicting the patterns A and
State the reason for the growth pattern seen in
Write the effects of the growth patterns seen above. [All India 2014]

Ans. (i) The organisms depicting pattern A are microorganisms while B depicts-zooplanktons or fishes.

(ii) With the increase in organic matter of lake due to influx of nutrients from agricultural land, the number of microorganisms increases to degrade the organic matter.

(iii) From the above growth patterns, it can be concluded that

(a) With the increase in microbes in water body the BOD increases, making it unfit for aquatic life.

(b) Dissolved oxygen reduces drastically leading to mortality of aquatic organisms, i.e. fishes.

28.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 the Delhi Government to improve the air quality. [Foreign 2014]

Write any two of your comments.
List any two ways that you would include in your programme so as to ensure the maintenance of good quality of air.
State any two values your programme will inculcate in the people of your locality. [Foreign 2014]

Ans.(i) The comments on the steps taken by

Delhi Government to improve air quality are:

(a) Switching over of entire public transport from diesel or petrol to CNG.

(b) Use of unleaded and low-sulphur petrol by vehicles.

(ii) The other two ways that can be included in the programme, so as to ensure maintenance of good quality of air can be:

Create awareness among people to switch over to CNG as it is less polluting as well as cost effective and phasing out of old vehicles.
Follow the routine pollution check according to pollution-level norms for vehicles and use catalytic convertors.

(iii) The programme can inculcate following values:

The people will become more responsible and guard their contributions towards air pollution.
Knowing the hazards and various consequences of pollutants, they will not indulge in activities esp. unauthorised and without having permission and prevent others from doing so.

29.A few residents in your locality, for business gains, have established small scale indsutrial/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. [All India 2014C]

Ans. No, these activities would not be supported, because

(i) The industrial activities will release its toxic gases into the atmosphere and other chemicals into the nearby water bodies without treating it and thus, causing pollution of air, water and soil.

(ii) The land acquired for operating these activities should be at a location where people or neighbourhood are least affected, so prior permission is mandatory.

(iii) Disposable waste of path labs can be infectious and toxic, also those including from other industries, so there needs to be a check on how the wastes are disposed off, segregated and recycled. (3)

30.Why should the spraying of DDT as an insecticide on vegetable crops be banned? Explain. [Delhi 2013c]

Ans. Spraying of DDT as an insecticide on vegetable crops should be banned because our foodgrains such as wheat, rice, fruits and vegetables accumulate the varying amount of insecticide residues and that enter the human body through food chain. As these chemicals are toxic and non-biodegradable, they get accumulated in organisms body and are difficult to excrete and their concentration goes on increasing

31.By the end of 2002, the public transport of Delhi switched over to a new fuel. Name the fuel. Why is this fuel considered better? Explain. [Delhi 2012]

Ans. Delhi had been categorised as the fourth most polluted city of the world in a list of 41 cities in the 1990s. Vehicular pollution has added to the pollution of air in Delhi. So, in year 2002, it switched over to a new fuel CNG (Compressed Natural Gas), Reasons of CNG being better fuel

(i) It is a clean fuel that produces very little unburnt particles. Hence, it is ecofriendly.

(ii) It burns most efficiently. Unlike petrol or diesel, very little is left unburnt.

(iii) It is cheaper and cannot be siphoned off by thieves and adulterated like petrol or diesel.

32.How does on algal bloom cause eutrophication of a water body? Name the weed that can grow in such a eutrophic lake. [Delhi 2012]

Ans. Algae are the major producers of any aquatic ecosystem. Run-off of nutrients such as animal wastes, fertilisers (N and P) and sewage from land leads to an increase in the fertility of the lake. It causes a tremendous increase in the primary productivity of the water body leading to increased growth of algae, resulting into algal bloom.

Later, the decomposition of these algae depletes the supply of oxygen, leading to the death of other aquatic animal life. This is called eutrophication.

Eichhornia crassipes (water hyacinth) also called Terror of Bengal can grow in such eutrophic lake

33.(i) Why are colourful polysterene and plastic packaging used for protecting the food, considered an environmental menace?

(ii) Write about the remedy found for the efficient use of plastic wastes by Ahmad Khan of Bengaluru. [Delhi 2012]

Ans. (i) Because polysterene and plastic are non-biodegradable, they accumulate and add to environmental pollution, hence are considered a menace.

(ii) Ahmad Khan developed a fine powder called polyblend of recycled modified plastic. This mixture is mixed with the bitumen and used to lay roads. It enhanced the bitumen’s water repellant properties and helped to increase road life by a factor of three. By this way, the problems created by plastic waste was solved.

34. (i) State the consequence if the electrostatic precipitator of a thermal plant fails to function.

(ii) Mention any four methods by which the vehicular air pollution can be controlled. [All India 2011]

Ans. (i) In the absence of electrostatic precipitator, the particulate pollutants and gaseous pollutants of the exhaust will enter into atmosphere. In case of ESPs, about 99% of particulate matter is absorbed.

(ii) General steps to reduce vehicular air pollution

Phasing out of old vehicles.
Use of unleaded petrol and low sulphur petrol and diesel.
Use of catalytic convertors in vehicles.
Application of Euro II norms for vehicles.

35. Eutrophication is the natural ageing of a lake. Explain. [Foreign 2011]

How does eutrophication lake take place? Explain. [Delhi 2011c]

Ans. The natural ageing of a lake is called eutrophication. In a young lake, there is very little life. Over the time, streams drain into it and water becomes enriched with nutrients like phosphate and nitrates.

As a result, phytoplanktons and some other plants flourish well. Due to this, the organic matter increases in lake, water becomes warmer and shallower. Hence, decomposers also start growing.

The high numbers of decomposers make use of large quantity of oxygen for decomposition. This leads to depletion of dissolved oxygen of the water and mortality of fish and other aquatic organisms. The eutrophied water bodies can lead to algal blooms, which further add organic matter in lake. These consume more oxygen leading to its depletion.

36.Explain biomagnification. How does the biomagnification of DDT affect the population of fish eating birds? [Foreign 2010]

Why is there a decline in the population of the fish eating birds, when the water body in amidst agricultural fields? [Delhi 2010c]

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. [All India 2009]

Ans. (i) Biomagnification can be defined as the

increase in concentration of toxicants at successive trophic levels.

(ii) Toxic substances accumulated by organism cannot be metabolised or excreted. Therefore, they get accumulated in an organism and passes on to higher trophic levels.

The population of fish eating birds living on the bank of a contaminated lake gets affected adversely by DDT. Being highly poisonous, DDT disturbs the calcium metabolism in birds which causes thinning of their egg shells and premature breaking of such eggs.

It leads to decline in the bird population.

37.A factory drains its waste water into the nearby lake. It has caused algal bloom.

How was the algal bloom caused?
What would be the consequences?
Name the phenomenon that caused it. [All India 2008]

Ans. (i) Due to large amount of nutrients like nitrate and phosphates present in waste water, algal blooms are formed.

(ii) Consequences of algal bloom

Deterioration of water quality.
Increased fish rnortility rate.
Some bloom-forming algae are toxic to human beings ar d animals.

(iii) This phenomenon is called accelerated eutrophication.

38.Study the graph given below and answer the questions that follow.

What is the relationship between dissolved oxygen and Biochemical Oxygen Demand (BOD)?
Mention their effect on aquatic life in the river. [All India 2008]

Ans. (i) As the BOD increase ., the amount of dissolved oxygen in the water body decreases sharply frcm the point of sewage discharge.

(ii) Effects on aquatic life

Causes high mortality of aquatic animals.
Algal blooms occur due to excessive growth of algae as the amount of nutrients is high.

39 Expand BOD.

At a particular segment of a river near a sugar factory, the BOD is much higher than the normal level. What is it indicative of? What will happen to the living organism in this part of the river?
Under what conditions will the BOD be lowered in the river? How will it affect the aquatic life? [Foreign 2008]

Ans. (i) BOD – Biochemical Ocygen Demand

(ii) It indicates the addtion of alot of organic matter. Microorganisms degrade it in the water body. Due to maximum consumption of oxygen by microbes during degradation process, dissolved oxygen gets reduced This leads to mortality of fish and other aquatic life.

(iii) When organic matter decrease and microbes do not require oxygen to further decompose it. the BOD will decrease, As a result, aquatic life will start flourishing again and the dissolved oxygen increases.

5 Marks Questions

40.(i) Why are catalytic convertors recommended for vehicles?

(ii) Why should such vehicles use only unleaded petrol?

(iii) Why is CNG preferred to diesel as a fuel in vehicles? [Delhi 2010]

Ans. (i) Catalytic convertor are used for reducing emission of poisonous gases like N0₂ and CO. When exhaust emission passes through catalytic convertor, nitric oxide splits into nitrogen and oxygen, carbon monoxide is oxidised into carbon dioxide and unburnt hydrocarbons get burnt completely into C0₂and H₂0

(ii) Such vehicles (with catalytic convertor)

should use unleaded petrol as leaded petrol inactivates the catalyst.

(iii) Delhi had been categorised as the fourth most polluted city of the world in a list of 41 cities in the 1990s. Vehicular pollution has added to the pollution of air in Delhi. So, in year 2002, it switched over to a new fuel CNG (Compressed Natural Gas), Reasons of CNG being better fuel

(i) It is a clean fuel that produces very little unburnt particles. Hence, it is ecofriendly.

(ii) It burns most efficiently. Unlike petrol or diesel, very little is left unburnt.

(iii) It is cheaper and cannot be siphoned off by thieves and adulterated like petrol or diesel.
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