NCERT 8th Class (CBSE) Science: Pollution of Water and Air

Question: What is the function of a catalytic converter?

Answer: To prevent vehicular pollution, new cars are fitted with a special system called catalytic converter. It can change harmful exhaust gases like carbon monoxide and nitrogen dioxide into harmless carbon dioxide, nitrogen and water.

Question: Name three greenhouse gases.

Answer: Carbon dioxide, Methane and Nitrous oxide.

Question: What should be done to reduce water pollution due to sewage and industrial waste?

Answer: Treating sewage and factory wastes before disposing them off so that water sources are not polluted.

Question: Rivers have always been used to dump waste. How is it that pollution of rivers is becoming more alarming now than it was earlier?

Answer:With an ever increasing human population and an increasing number of industries, the amount of waste which goes into the water is very high. Therefore, the natural process of decay of the wastes can not cope with the amount of waste dumped.

Question: What are the cause and effects of eutrophication?

Answer: Excessive run off of fertilizers into water sources results in an increase in nutrients in water. This though a chain reaction leads to excessive plant growth and depletion of oxygen in water. The condition is known as eutrophication. It adversely affects the water plants and animals.

Question: Give four methods of conserving water.

Answer: Some of the methods of water conservation are as follows:

1. Using less water and avoiding wastage at home.
2. Using better methods of irrigation.
3. Recycling of water in factories and using it several times before it is disposed off.
4. Treating sewage and factory wastes before disposing them off.
5. Water harvesting of rainwater to raise the groundwater level.

Question: What is SPM? What harm does SPM pollution cause?

Answer: Minute solid particles suspended in air are known as Suspended Particulate Matter or SPM. Unburnt carbon particles given out during the burning of fuels or from the exhausts of vehicles, and fine particles of cement given out from a cement factory are examples of SPM. The finer of these particles cannot be filtered by the hair in our noses and hence are a major cause of lung diseases. They also settle on plants and interfere with photosynthesis.