Our Environment: Class 10 Important Questions with Answers

Case-based questions (4 marks each)

(i) Name the trophic level of the fox. (1) (ii) Energy available to the fox and the wolf. (1) (iii) What happens to rabbits, grass and wolves if foxes are wiped out? Why does the chain stop at four levels? (2)

(i) Name the phenomenon. (1) (ii) Why does the concentration rise at each level? (1) (iii) Why are the birds most affected, and how could humans be harmed? Suggest one step to prevent this. (2)

(i) Write the reactions by which ozone forms. (1) (ii) How do CFCs affect us? (1) (iii) What agreement was made in 1987, and why is the hole closing? (2)

(i) What fraction is biodegradable? (1) (ii) Suggest the best way to handle the biodegradable part. (1) (iii) Give two harms of throwing the rest in an open dump, and two ways the school can reduce it. (2)

20 MCQs (1 mark each)

1. An abiotic component is
   (a) bacteria (b) soil (c) grass (d) frog
2. An artificial ecosystem:
   (a) pond (b) forest (c) aquarium (d) lake
3. Producers are
   (a) heterotrophs (b) autotrophs (c) saprophytes (d) parasites
4. Decomposers are
   (a) bacteria and fungi (b) green plants (c) insects (d) viruses only
5. Herbivores occupy
   (a) T1 (b) T2 (c) T3 (d) T4
6. Greatest number of individuals at
   (a) T1 (b) T2 (c) T3 (d) top
7. Energy reaching the next level:
   (a) 1% (b) 10% (c) 50% (d) 90%
8. Producers have 1000 J; T3 gets
   (a) 100 J (b) 10 J (c) 1 J (d) 0.1 J
9. Flow of energy in an ecosystem is
   (a) cyclic (b) unidirectional (c) two-way (d) random
10. Food chains are limited to 3–4 steps because
    (a) too many animals (b) energy loss at each step (c) no plants (d) decomposers
11. A food web is more stable because
    (a) fewer organisms (b) alternative food sources (c) no predators (d) more sunlight
12. Maximum pesticide concentration is in
    (a) producers (b) herbivores (c) top consumers (d) decomposers
13. Ozone is
    (a) O (b) O₂ (c) O₃ (d) CO₂
14. Ozone layer protects from
    (a) infrared (b) UV (c) visible light (d) radio waves
15. Main cause of ozone depletion:
    (a) CO₂ (b) CFCs (c) O₂ (d) N₂
16. CFC production was frozen at the level of
    (a) 1980 (b) 1986 (c) 1987 (d) 1990
17. Biodegradable item:
    (a) polythene (b) glass (c) vegetable peel (d) DDT
18. Plastics are not decomposed because
    (a) microbes lack enzymes for them (b) they are heavy (c) they are coloured (d) they dissolve
19. Which group is a food chain?
    (a) grass, wheat, mango (b) grass, goat, human (c) goat, cow, elephant (d) grass, fish, goat
20. Large-scale kulhads were rejected because they
    (a) break (b) waste fertile top-soil (c) are costly (d) are plastic

Answer key

Why: 8 → 1000 × 1/10 × 1/10 = 10 J (T1 → T2 → T3).

Assertion–Reason (10)

(a) Both A and R true, R explains A · (b) Both true, R does not explain A · (c) A true, R false · (d) A false, R true

1. A: A garden is an ecosystem. R: It has living organisms interacting with abiotic factors. → (a)
2. A: Food chains have 3–4 steps. R: Only 10% of energy passes to the next level. → (a)
3. A: Energy flow is unidirectional. R: Energy passed to herbivores does not come back to plants. → (a)
4. A: Humans have the highest concentration of pesticides. R: Humans are at the top of most food chains. → (a)
5. A: Decomposers are important. R: They make food by photosynthesis. → (c)
6. A: Ozone at ground level is useful for breathing. R: Ozone absorbs UV radiation. → (d)
7. A: CFC-free refrigerators are mandatory. R: CFCs deplete the ozone layer. → (a)
8. A: Plastics persist in the environment. R: Enzymes are specific in their action. → (a)
9. A: An aquarium needs cleaning. R: It is a natural ecosystem. → (c)
10. A: A food web is more stable than a food chain. R: In a food web organisms have alternative foods. → (a)

Give reasons (2 marks each)

1. The number of producers is the largest in an ecosystem.

Only 10% of energy passes up each level, so a large base of producers is needed to support the fewer consumers above. 2

2. Pesticide residues remain in vegetables even after washing.

Plants absorb them from the soil along with water, so they are inside the tissues, not just on the surface. 2

3. Paper cups are better than plastic cups.

Paper is biodegradable and made from renewable material; plastic cups persist and pollute. 2

4. Ozone depletion is a global concern.

The ozone layer shields all life on earth from UV; its loss increases skin cancer and harms crops and plankton everywhere. 2

5. Removing decomposers would harm the ecosystem.

Dead matter would pile up and nutrients would not return to the soil, so plants would not get minerals. 2