NCERT Class VIII Science Solutions: Chapter 18-Pollution of Air and Water Part 3

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Question 8:

Describe the ‘Green House Effect’ in your own words.


Green House effect is a process by which solar radiation is absorbed by greenhouse gases and the temperature of Earth atmosphere is increased. This increase in the temperature of the surroundings is responsible for global warming. Gases like, Methane, nitrous oxide, water vapour, etc. trap heat radiation and are called greenhouse gases.

Green houses are often used for growing flowers, vegetables and plants (Mainly in cold region). Now because of increase in concentration of greenhouse gases in our environment is adversely affecting the climate.

Result for Green House Effect

Green House Effect

Question 9:

Prepare a brief speech on global warming that you have to make in your class.


Continuous increase in temperature of the Earth due to increase levels of greenhouse gases is known as Global warming. Global warming is one of the biggest concern worldwide. Scientists believe climate shifting, melting of glaciers (e.g. Gangotri glacier), sudden floods in coastal areas are due to global warming. The Kyoto Protocol is one such agreement made among the countries to reduce emission of greenhouse gases. Small contributions on our part can make a huge difference in the state of the environment. We can plant trees and nurture the ones already present in the neighborhood.

Question 10:

Describe the threat to the beauty of the Taj Mahal.


Due to increase of gases like sulphur dioxide and nitrogen dioxide, acid rain take place. Acid rain corrodes the marble of the monument. The phenomenon is also called “Marble cancer”. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards yellowing of the marble.

Image result for beauty of the Taj Mahal

Beauty of the Taj Mahal

Question 11:

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


Excessive quantities of chemicals (fertilizers, weedicides, pesticides etc.) washed from the fields enter into ponds. These act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. In this process a lot of oxygen in these ponds gets used up. This results in a decrease in the oxygen level, which kills aquatic organisms.

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