Question Bank — Our Environment

NCERT Class 10 Science · Chapter 13 · CBSE Board Pattern

Class 10 Science Chapter 13 Question Bank CBSE Board Pattern

Section A — MCQs (10 questions, 1 mark each)

  1. Which of the following represents a human-made ecosystem?
    (a) Forest
    (b) Pond
    (c) Crop-field
    (d) Lake

  2. In a food chain, the maximum concentration of non-biodegradable pesticides is likely to be found in
    (a) producers
    (b) primary consumers
    (c) secondary consumers
    (d) tertiary consumers

  3. The ozone layer protects the Earth from
    (a) infrared radiation
    (b) ultraviolet radiation
    (c) visible light
    (d) radio waves

  4. Which of the following is a biodegradable substance?
    (a) Plastic
    (b) Glass
    (c) Vegetable peels
    (d) Synthetic fibre

  5. The flow of energy in an ecosystem is
    (a) bidirectional
    (b) cyclic
    (c) unidirectional
    (d) random

  6. Decomposers are important because they
    (a) produce food using sunlight
    (b) convert complex organic matter into simple inorganic substances
    (c) consume plants only
    (d) increase the number of trophic levels

Assertion-Reason Questions

  1. Assertion (A): Food chains generally have only three or four trophic levels.
    Reason (R): There is a progressive loss of energy at each trophic level and very little usable energy remains after four levels.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

  2. Assertion (A): The amount of ozone in the atmosphere began to drop sharply in the 1980s.
    Reason (R): Synthetic chemicals like CFCs used in refrigerators and fire extinguishers react with ozone and deplete it.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

  3. Which of the following correctly shows the order of organisms in a simple food chain?
    (a) Grass → Frog → Snake → Eagle
    (b) Eagle → Snake → Frog → Grass
    (c) Snake → Eagle → Grass → Frog
    (d) Frog → Grass → Snake → Eagle

  4. Biological magnification refers to
    (a) increase in number of organisms at higher trophic levels
    (b) progressive accumulation of non-biodegradable chemicals at successive trophic levels
    (c) loss of energy at each trophic level
    (d) conversion of solar energy into chemical energy by producers

Section B — Very Short Answer (6 questions, 2 marks each)

  1. Define trophic level. Give one example of the first trophic level in a grassland ecosystem.

  2. Why is an aquarium considered a human-made ecosystem? State one reason why it needs to be cleaned periodically.

  3. What is the role of decomposers in an ecosystem? What would happen to dead organic matter in their absence?

  4. State the 10% law of energy transfer in a food chain. How does this law limit the length of food chains?

  5. Differentiate between biodegradable and non-biodegradable substances with one example of each.

  6. Name the chemicals responsible for ozone layer depletion. Why is damage to the ozone layer a cause for concern?

Section C — Short Answer (5 questions, 3 marks each)

  1. Describe the components of an ecosystem with suitable examples. How do biotic and abiotic components interact?

  2. Draw a simple food chain consisting of four organisms. Label the different trophic levels and indicate the direction of energy flow.

  3. Explain the phenomenon of biological magnification using the example of pesticides entering a food chain. Why do human beings receive the maximum concentration?

  4. What are the problems caused by non-biodegradable wastes in the environment? Give two examples of such wastes.

  5. How does the ozone layer form in the upper atmosphere? Write the chemical equation involved and state its importance for living organisms.

Section D — Long Answer (3 questions, 5 marks each)

  1. What is a food web? How is it different from a food chain? Explain with the help of a labelled diagram showing at least three interconnected food chains in a forest ecosystem. (Diagram required)

  2. Explain the flow of energy in an ecosystem with the help of a labelled diagram. Why is the flow unidirectional and why does the amount of energy decrease at successive trophic levels? (Diagram required)

  3. (a) What are the various methods by which we can reduce the problem of waste disposal?
    (b) Why is separating biodegradable and non-biodegradable waste important? Explain with examples from daily life.

Section E — Case/Source-Based (2 questions, 4 marks each)

Case 1:

In a school project, students set up an aquarium with fish, aquatic plants, water and an aerator. After a few weeks, some fish died. The students observed that dead plant material and fish remains were accumulating at the bottom.

  1. Identify the role of aquatic plants in this setup.
  2. Which group of organisms would break down the dead remains if added to the aquarium?
  3. Why did the accumulation of dead matter occur?
  4. Suggest one change the students could make to make the aquarium more self-sustaining.

Case 2:

A news report stated that pesticide residues were detected in vegetables and grains sold in markets. Scientists linked this to chemicals sprayed on crops that entered the soil and water bodies.

  1. Name the process by which these chemicals accumulate in the bodies of organisms at higher trophic levels.
  2. Which trophic level organisms would show the highest concentration of these chemicals?
  3. Why cannot these chemicals be removed completely by washing vegetables?
  4. Suggest one method to reduce the entry of such chemicals into the human food chain.

Section F — HOTS and Application (4 questions, 3 marks each)

  1. Predict-and-justify: What would happen to the population of primary consumers and producers if all the tertiary consumers in a forest ecosystem suddenly disappeared? Justify your answer.

  2. Analyse an unexpected observation: In an experiment, students observed that a plastic bottle buried in soil remained unchanged even after three months, while vegetable peels decomposed completely. Explain this observation using the concepts of biodegradability.

  3. Apply to unfamiliar situation: In a newly developed residential colony, residents started dumping kitchen waste and plastic wrappers in an open plot. Predict the long-term effect on the soil and surrounding water bodies if this practice continues.

  4. Compare two situations: In Situation A, all waste generated in a locality is biodegradable. In Situation B, a large amount of non-biodegradable plastic is also generated. In which situation will the impact on the environment be more harmful and why?

▶ Answer Key Attempt all questions first,
then tap to reveal

Section A

  1. (c)
  2. (d)
  3. (b)
  4. (c)
  5. (c)
  6. (b)
  7. (a)
  8. (a)
  9. (a)
  10. (b)

Section B

  1. Trophic level is a step in the food chain (1 mark). First trophic level in grassland: grass/producers (1 mark).
  2. It is artificial/human-made (1 mark); needs cleaning because waste accumulates as it is not fully self-sustaining (1 mark).
  3. Break down complex organic matter into simple inorganic substances (1 mark); without them, dead matter would accumulate and soil would not be replenished (1 mark).
  4. Only 10% of energy is transferred to the next level (1 mark); limits food chains to 3–4 levels due to energy loss (1 mark).
  5. Biodegradable: broken down by biological processes (e.g., vegetable peels) (1 mark); Non-biodegradable: not broken down (e.g., plastic) (1 mark).
  6. CFCs (1 mark); UV radiation reaches Earth causing skin cancer and harming organisms (1 mark).

Section C

  1. Biotic (producers, consumers, decomposers) and abiotic (temperature, rainfall, soil) components (2 marks); interaction maintains balance (1 mark).
  2. Correct food chain with four organisms + labelled trophic levels + energy flow arrow (1+1+1 marks).
  3. Chemicals enter via plants/aquatic organisms and accumulate at each level (2 marks); humans at top trophic level get maximum concentration (1 mark).
  4. Persist for long time, harm organisms, pollute soil/water (2 marks); examples: plastic, glass (1 mark).
  5. UV splits O₂ into O atoms which combine with O₂ to form O₃ (2 marks + equation); protects from harmful UV radiation (1 mark).

Section D

  1. Food web = interconnected food chains (2 marks); difference from food chain (1 mark); labelled diagram with 3 chains (2 marks).
  2. Diagram showing unidirectional flow and 10% transfer (3 marks); explanation of energy loss at each level (2 marks).
  3. (a) Segregation, composting, recycling (2 marks); (b) Prevents accumulation of persistent waste and allows natural decomposition (3 marks).

Section E

Case 1: 1. Producers (1); 2. Decomposers/bacteria & fungi (1); 3. No decomposers present (1); 4. Add decomposers or reduce feeding (1).
Case 2: 1. Biological magnification (1); 2. Tertiary/humans (1); 3. Chemicals are non-biodegradable (1); 4. Use organic farming/reduce pesticide use (1).

Section F

  1. Primary consumers increase → overgrazing → producers decrease (reasoning chain with energy/population link).
  2. Plastic is non-biodegradable; vegetable peels are biodegradable (specific enzyme action).
  3. Soil pollution, groundwater contamination, harm to decomposers and aquatic life.
  4. Situation B more harmful because non-biodegradable waste persists and causes long-term damage.
← Revision Summary All Chapters

All questions are answerable from the NCERT chapter text. Reviewed by GFIS faculty.