In a village, farmers started cultivating crops all around a lake which was always filled with water. They added lot of materials W to the soil in their fields to increase the yield of crops. Soon they found that the whole surface of water in the lake was covered with a green layer made up of tiny organisms X. After some time, the fish present in the lake started dying in large numbers because they could not get sufficient Y due to a process Z which had occurred in lake water and drained out all the Y present in the water of lake.

1. What do you think materials W are?
2. Name (i) X, and (ii) Y.
3. What is the process Z known as?
4. What happens during the process Z which uses up all the Y present in lake water?
5. What does this example tell us about the use of materials like W?

(a) The materials W is fertilizer as when it is added to the soil in fields, it will increase the yield of crops

(b) (i) X is algae as they are tiny organisms and made a green layer to cover the whole surface of water in the lake, and

(ii) Y is oxygen as its insufficient quantity in the lake leads to the death of the fish in large numbers.

(c) The process Z is known as eutrophication.

(d) During the process of eutrophication (Z), when the algae die, bacteria present in the lake water decay the algae.

(e) This example explains that the excessive usage of materials like fertilizers (W) is toxic and hazardous for the environment.

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Updated on: 20-Mar-2023

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