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Class 10 Science: Our Environment, 8 practice questions with answers

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These are 8 practice questions on NCERT Class 10 Science Chapter 13, Our Environment, each with a worked answer and the textbook page it comes from. Four are numericals on the 10% rule for energy in a food chain, and the rest cover trophic levels, why food chains are short, biodegradable waste and the ozone layer. Try each one before you read the answer.

These questions are our own, drafted with AI help. Every number was re-computed by a test script and every statement was checked against the chapter, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

Food chains and energy

Question 1. What is each step in a food chain called?

Answer: a trophic level. A series of organisms feeding on one another forms a food chain, and each step or level of the food chain forms a trophic level. (Section 13.1.1, page 210.)

Question 2. Assertion (A): Food chains usually have only three or four steps. Reason (R): Only about 10% of the food at one level is made available to the next level. Choose the correct option: both true and R explains A; both true but R does not explain A; A true and R false; or A false and R true.

Answer: A and R are both true, and R explains A. An average of 10% of the food eaten is turned into the consumer's own body and made available to the next level. Since so little energy is available for the next level, food chains generally consist of only three or four steps; very little usable energy remains after four trophic levels. (Page 210.)

Question 3. Producers in a field store 20,000 J of energy. Using the 10% rule, about how much energy is available to the herbivores that eat them, in joules?

Answer: 2,000 J. About 10% passes to the next level: 20,000 × 10 ÷ 100 = 2,000 J. (Page 210.)

Question 4. Producers store 50,000 J. Using the 10% rule, about how much energy reaches the secondary consumers (two levels up), in joules?

Answer: 500 J. Herbivores get 10% of 50,000 = 5,000 J. Secondary consumers get 10% of 5,000 = 500 J. (Page 210.)

Question 5. Green plants turn only about 1% of the sunlight that falls on their leaves into food energy, and about 10% of the energy passes from one trophic level to the next. (a) For 20 J to reach the fourth trophic level, how much energy must the producers hold? (b) How much sunlight energy must fall on the plants for that, in joules?

Answer: (a) The fourth level is three steps above the producers, so producers × 0.1 × 0.1 × 0.1 = 20, and producers = 20 ÷ 0.001 = 20,000 J. (b) Plants keep about 1% of the sunlight: sunlight = 20,000 ÷ 0.01 = 2,000,000 J. (The textbook states that green plants capture about 1% of the sunlight that falls on their leaves, and the 10% average, page 210.)

Waste and the ozone layer

Question 6. Which of these kitchen wastes is biodegradable? (Vegetable peels; an empty medicine strip; or a bubble pack.)

Answer: vegetable peels. Substances that are broken down by biological processes are biodegradable; those that are not are non-biodegradable and may persist in the environment for a long time. Vegetable peels are broken down; plastic packs persist. (Page 214.)

Question 7. Which synthetic chemicals have been linked to the drop in the amount of ozone in the atmosphere since the 1980s? (Fertilisers; common salt; or chlorofluorocarbons, CFCs.)

Answer: chlorofluorocarbons (CFCs). The amount of ozone began to drop sharply in the 1980s, and the decrease has been linked to synthetic chemicals like CFCs, which are used as refrigerants and in fire extinguishers. (Page 213.)

Question 8. In 1987 the United Nations Environment Programme (UNEP) made an agreement about CFCs. What was it?

Answer: UNEP succeeded in forging an agreement to freeze CFC production at 1986 levels. (Page 213.)

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Sources

All opened and read on 21 October 2026. Page numbers are the printed page numbers of the textbook.

The facts are from the textbook pages above. The questions, worked answers and checks are our own, and every number was re-computed by script. This guide is general information; follow your teacher and the textbook.