Pollution of Air and Water (Biology) Class 8 - NCERT Questions

Q 1.

What are the different ways in which water gets contaminated?


Water gets contaminated by following ways:
(i) Water gets contaminated when sewage is disposed off in rivers.
(ii) Chemicals which are harmful and poisonous are thrown in water resources by various industrial units.
(iii) Harmful chemicals used in agricultural processes gets mixed with ground water making it unfit for consumption.
(iv) Breeding of microorganisms in water make water polluted

Q 2.

At an individual level, how can you help reduce air pollution?


We can plant trees to reduce the level of carbon dioxide. We can get our vehicles serviced well to reduce incomplete combustion of fuels. We can also reduce air pollution by saying no to crackers during Diwali celebrations.

Q 3.

Clear, transparent water is always fit for drinking. Comment.


Water which looks clean and transparent is not always fit for drinking. It may still have disease carrying microorganisms and dissolved impurities.

Q 4.

You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.


To supply clean water in every household,
(i) it is necessary that water reaching houses should be treated water. Water should be treated in sewage plants, to make it free from physical, chemical and biological impurities.
(ii) strict laws should be enforced on industrial units, which dispose polluted water in water resources.
(iii) open defecation in water resources by slum dwellers should be strictly prohibited.
(iv) chlorine tablets should be distributed for purification of water during rainy season.
(v) people should be made aware and motivated to keep water resources clean.

Q 5.

Explain the differences between pure air and polluted air.


Pure air is free from harmful gases which can be poisonous in nature. Pure air has balanced quantity of all its constituent gases and it is free from germs. This type of air is fit for breathing. On the other hand polluted air has poisonous gases and other suspended impurities like dust and smoke. It is unfit for consumption.

Q 6.

Explain circumstances leading to acid rain. How does acid rain affect us?


Acid rain is caused due to mixing of poisonous gases with rain. When our industrial units emit poisonous gases like sulphur dioxide and nitrogen dioxide, these gases react with moisture present in air and form sulphuric acid and nitric acid respectively. These acids fall on the earth with rain making rain water acidic and harmful.
Acid rain causes the corrosion of buildings and make food grains, fruits and vegetables unfit for consumption.

Q 7.

Which of the following is not a greenhouse gas?
(A) Carbon dioxide
(B) Sulphur dioxide
(C) Methane
(D) Nitrogen


Sulphur dioxide and Nitrogen.

Q 8.

Describe the `Greenhouse Effect’ in your own words.


Greenhouse effect means warming the environment. When the rays of sun reach earth, some of the radiations are absorbed by the earth and rest of them are reflected back by the earth. A part of the reflected radiation is trapped by the atmosphere. This causes further warming of the earth, which is necessary for the sustaining life. This traptrapping of the heat is called green house effect.

Q 9.

Prepare a brief speech on global warming. You have to deliver the speech in your class.


Continuous increase in the temperature of the earth is called global warming. CO2, methane, nitrous oxide and water vapour are the greenhouse gases that lead to this effect. Among these gases, CO2 is the main contributor of the global warming. CO2 traps heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming. Global warming can cause sea levels to rise dramatically. In many places, coastal areas have already been flooded. Global warming could result in wide ranging effects on rainfall patterns, agriculture, forests, plants and animals. Majority of people living in regions which are threatened by global warming are in Asia. A recent climate change report gives us only a limited time to keep the greenhouse gases at the present level. Otherwise, the temperature may rise by more than 2 degrees celsius by the end of the century, a level considered dangerous.

Q 10.

Describe the threat to the beauty of the Taj Mahal.


Increasing air pollution has posed a threat to the beauty of the Taj Mahal. Excessive poisonous gases and smoke has started to discolour (yellowing) the white marble of the Taj Mahal. Acid rains due to increasing air pollution has started corroding the marble, thus making Taj Mahal lose its beauty.

Q 11.

Why does the increased level of nutrients in the water affect the survival of aquatic organisms?


Addition of nutrients in water flourishes the growth of microorganisms like algae which use up the dissolved oxygen from the water. When algae die, they become food for decomposers such as bacteria they also use the dissolved oxygen, thus reducing oxygen content even further. Their thick growth also stops sunlight from reaching the water. This enrichment of water by nutrients which leads to excessive plant growth and depletion of oxygen is known as eutrophication. Decrease in oxygen in water, becomes trouble for other aquatic organisms and they start dying due to insufficient amount of oxygen to breathe.