Board Previous Year Questions (PYQs)
Arranged by marks. Environment is a 5-mark unit - focus on clear definitions, examples and reasoning; draw labelled diagrams (food chain, energy pyramid) where asked.
1-Mark Questions
Q1. Name the organisms that occupy the first trophic level of a food chain. (Ans: producers / green plants.)
Q2. Give one example of a non-biodegradable substance. (Ans: plastic / glass / DDT.)
Q3. What percentage of energy is transferred to the next trophic level? (Ans: about 10%.)
Q4. Which gas layer protects us from UV radiation? (Ans: the ozone (O₃) layer.)
Q5. Name the chemicals responsible for ozone depletion. (Ans: chlorofluorocarbons, CFCs.)
2-Mark Questions
Q6. What is the role of decomposers in an ecosystem? Ans: Decomposers (bacteria and fungi) break down dead remains and waste into simple inorganic substances that return to the soil, recycling nutrients for producers and keeping the ecosystem clean.
Q7. Why is a food web more stable than a food chain? Ans: In a food web each organism has alternative food sources. If one species declines, others use different pathways, so the ecosystem is disturbed less - giving greater stability than a single food chain.
Q8. Give two ways non-biodegradable waste harms the environment. Ans: (i) It persists and pollutes soil and water and can harm/kill animals that ingest it. (ii) Non-degradable chemicals enter food chains and biomagnify to harmful levels in top consumers.
3-Mark Questions
Q9. What are trophic levels? Give a food chain and mark its trophic levels. (NCERT) Ans: A trophic level is each feeding step of a food chain. Grass → grasshopper → frog → snake: grass = producer (T1), grasshopper = primary consumer (T2), frog = secondary (T3), snake = tertiary (T4).
Q10. State the ten per cent law. Why do food chains have only 3-4 steps? Ans: Only about 10% of the energy at a trophic level passes to the next; ~90% is lost as heat. Because so little energy remains after each step, after 3-4 levels too little usable energy is left to support another level.
Q11. What is biological magnification? Why is its effect greatest in humans? Ans: It is the increasing concentration of non-degradable chemicals up a food chain. Since humans are usually at the top of food chains, these chemicals accumulate to their maximum concentration in human bodies.
5-Mark Questions
Q12. (a) Define an ecosystem and name its components. (b) With a diagram, explain energy flow through a food chain. (c) State the ten per cent law. Ans: (a) An ecosystem is all interacting organisms plus the abiotic surroundings; components = biotic (producers, consumers, decomposers) and abiotic (temperature, water, soil, etc.). (b) Energy flows Sun → producers → herbivores → carnivores → decomposers (draw an energy pyramid); it is unidirectional and decreases at each level. (c) Ten per cent law: only ~10% of energy at one trophic level reaches the next.
Q13. (a) What is ozone? (b) How is it formed and how does it protect us? (c) Why is its depletion a concern and what has been done? (NCERT) Ans: (a) Ozone (O₃) is a molecule of three oxygen atoms. (b) High in the atmosphere UV splits O₂ into O atoms which combine with O₂ to form O₃; the ozone layer absorbs harmful UV radiation. (c) Depletion by CFCs lets more UV reach Earth (causing skin cancer, etc.); the 1987 UNEP agreement froze CFC production and CFC-free products are now mandatory.
Q14. Distinguish biodegradable and non-biodegradable substances with examples, and give the problems each can cause and two ways to help. Ans: Biodegradable - broken down by microbes (peels, paper, cloth, food); if unmanaged cause smell, disease, water pollution. Non-biodegradable - not broken down (plastic, glass, metal, DDT); persist, pollute and biomagnify. Help: segregate and compost/recycle waste; reduce and reuse (cloth bags, avoid single-use plastics).