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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
Which pollutant is released from the paddy fields ?


What measures, as an individual, you would take to reduce environmental pollution ?

To reduce environmental pollution one can take the following measures:
1. Use of unleaded petrol or CNG in vehicles as fuel.
2. Use of catalytic converters in automobiles.
3. Avoiding the use of chloroflurocarbons to save ozone in the atmosphere.
4. Recycling and reuse of plastic and paper.
5. Plantation of more and more trees.
6.  Optimizing the use of water.
7. Use of biodegradable material should be used.
8. Avoid burning crackers on Diwali.
9. Keeping radio, transistors, T.V., music system at low volume to control noise pollution.
10.Practising organic farming and avoiding excessive use of agro-chemicals.



Discuss the causes and effects of global warming. What measures need to be taken to control global warming?

Global warming. The increase in global mean temperature due to enhanced greenhouse effect is called global warming. The greenhouse gases like carbon dioxide and methane trap heat energy and keep the Earth's atmosphere warm. The increased level greenhouse gases has led to considerable heating of Earth leading to global warming. The increased level of greenhouse gases is because of rapid industrialisation, burning of fossil fuels and deforestation.
Effects of global warming : Global warming will have harmful effects on Earth. It will lead to rise in the average temperature of earth, which may increase by 1.4° to 5.8°C by the year 2100. It will lead to melting of polar ice caps and lead to rise in Sea level. The rise in sea level may in turn lead to the submergence of the coastal areas. Climatic change is threat to human health in tropical and subtropical countries. It will also create imbalance in the water cycle of Earth. Global warming will have harmful effect on the organisms be it plants or animals.

The measures that need to be taken to control global warming are:
(i) Reducing the use of fossil fuels.
(ii) Reforestation or planting of more and more trees.
(iii) Use of Bio-fuels.
(iv) Improving efficiency of energy usage.
(v) Reducing the emission of greenhouse gases in the atmosphere.


Write critical notes on the following:
(a) Eutrophication
(b) Biological magnification
(c) Groundwater depletion and ways for its replenishment


(a) Eutrophication. The process by which a body of water becomes

barren either by natural means or by pollution, extensively rich in dissolved nutrients. It results in the increased primary productivity that often leads to seasonal deficiency in dissolved oxygen.

Algal bloom. Phosphorus and nitrates dissolved in water act as nutrients and accelerate the growth of algae that may form a mat on the water surface. It is termed algal bloom.

Effects. The algae use oxygen at night and may deoxygenate the water enough to kill the fish and other animals. The algal mat at the water surface may block light to the submerged plants. The algae may die and sink, and feed the oxygen-consuming bacteria. They may be pushed on to the shore by wind and decompose, releasing foul gases, such as hydrogen sulphide. Silt and decaying matter may accumulate and finally fill the lake or pond. This process is called senescence. It is a natural stage in the change of a lake into dry land and it becomes barren, ultimately death of lake occurs.

(b) Biological magnification (Bio-magnification). The phenomenon in which the harmful pollutants (such as pesticides) enter the food chain and get concentrated more and more at each successive trophic level of organisms is called biological magnification.

This phenomenon is well known for mercury and DDT. Figure on the side shows biomagnification of DDT in an aquatic food chain. Zooplankton (tiny floating animals) in the food chain, accumulated modest levels of DDT. However, small fish, forming the next level of the food chain, must eat zooplankton several times their own weight and thus they accumulated more of DDT. In this manner, the concentration of DDT magnified at successive trophic levels, starting with 0.003 ppb (ppb = parts per billion) in water it ultimately reached 25 ppm (ppm = parts per million) in fish-eating birds.

High concentrations of DDT disturb calcium metabolism in birds. It causes thinning of egg shell and their premature breaking. Thus, there is decline in bird population.

(a) Eutrophication. The process by which a body of water becomes

â–² Fig. 8.1. Biomagnification of DDT in an aquatic food chain.

(c) Ground water depletion and ways for its replenishment

Underground water is more pure and safe for drinking. It is getting polluted

particularly in industrial towns. The common sources of underground water pollution are sewage and industrial effluents spilled over the ground. The fertilizers and pesticides used in fields also act as pollutants. Pollution is also increased due to seepage from refuse dumps, septic tanks and seepage pits.

Method to control. Sewage and factory wastes should be treated to clean them before their release into water sources.


What are various constituents of domestic sewage ? Discuss the effects of sewage discharge on a river.

Constituents of domestic sewage.
It mainly consists of biodegradable organic matter
(i) suspended solids e.g., sand, silt and clay.
(ii) colloidal materials eg. faecal matter, bacteria, disease causing microbes, cloth fibre, plastic and paper.
(iii)Dissolved materials, e.g. nutrients (nitrates, ammonia, phosphates, sodium and calcium).

Effects of Sewage discharge on a river : 
(i) The micro-organisms in the sewage consume alot of oxygen and this pose a problem for other organisms in the river.
(ii) The Biochemical oxygen demand (BOD) of the river increases.
(iii) Presence of large amount nutrients causes excessive growth of planktonic algae or Algal bloom which imparts distinct color and degrades the quality of water and fish mortality. Some bloom-forming algae are extremely toxic to human beings and animals.
(iii) Various disease causing microbes  may cause outbreak of serious diseases, such as, dysentery, typhoid, jaundice, cholera, etc


A. Catalytic converter (i) Particulate matter
B. Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides
C. Earmuffs (iii) High noise level
D. Landfills (iv) Solid wastes


Catalytic converter


Carbon monoxide and nitrogen oxides


Electrostatic precipitator


Particulate matter




High noise level




Solid wastes