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Our Environment Practice

Solve chapter-level practice questions for Our Environment with reveal-only solutions and quick revision support.

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Practice Set 1 — Ecosystem and Energy Flow

Components of an ecosystem, food chains, and the 10% law.

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Q1. What is an ecosystem? Give one natural and one artificial example.
Q2. Why are decomposers important for an ecosystem?
Q3. State the 10 per cent law of energy flow.
Q4. Why are food chains usually limited to 4 or 5 trophic levels?
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Q5. Give one difference between a food chain and a food web.
Q6. In a food chain, which trophic level always has the maximum energy available to it?

Practice Set 2 — Human Impact on the Environment

Biodegradable waste, biological magnification, and ozone depletion.

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Q1. Classify the following as biodegradable or non-biodegradable: paper, polythene bag, cow dung, aluminium wrapper, cotton cloth, DDT.
Q2. What is biological magnification? Why are its effects worst for organisms at the top of a food chain?
Q3. How is the ozone layer useful to us, and how is it being damaged?
Q4. What steps were taken internationally to protect the ozone layer?
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Q5. Give two ways you can reduce the generation of non-biodegradable waste at home.
Q6. Why should biodegradable and non-biodegradable wastes be collected separately?

Quick Q&A Before You Revise

Why is the flow of energy in an ecosystem said to be unidirectional?

Energy captured by producers moves to herbivores, then to carnivores, and is finally lost as heat. It does not flow back from consumers to producers or from the Earth to the Sun, so it moves only in one direction.

What will happen if we kill all the organisms in one trophic level?

The organisms in the next higher level will lose their food and decline, while the level below will increase because nothing is eating it. The whole ecosystem is disturbed, though a rich food web can partly absorb the shock.

Why are some substances biodegradable and some non-biodegradable?

Biodegradable substances have chemical bonds that the enzymes of decomposer bacteria and fungi can break. Non-biodegradable substances (like many plastics) have bonds that these enzymes cannot act on, so they are not broken down naturally.

Will the impact of removing all the decomposers be equally harmful for an ecosystem as the removal of all the producers?

Both are extremely harmful. Without producers there is no food or energy input. Without decomposers, dead matter piles up and nutrients are not recycled, so producers eventually run out of raw materials. The ecosystem collapses in either case.

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