Our Environment is the closing chapter of Class 10 Science and the current, correct Chapter 13 in the 2023-rationalised, 2026-27 session NCERT textbook — it was Chapter 15 in the pre-2023 book. It covers ecosystems, food chains and food webs, the ozone layer, and how we manage the waste we generate. Below are complete, original answers to all 16 end-of-chapter exercise questions, cross-checked against multiple current sources. These Class 10 Science Chapter 13 solutions are also useful as quick revision notes before exams.
NCERT Solutions for Class 10 Science Chapter 13: Our Environment
Q1. Why are some substances biodegradable and some non-biodegradable?
Biodegradable substances (e.g. vegetable peels, paper, cotton, wood) have a chemical structure that decomposer microorganisms (bacteria, fungi) can break down into simpler, natural substances using their enzymes. Non-biodegradable substances (e.g. plastic, polythene, DDT, glass) have a structure that these enzymes cannot act on, so they persist in the environment instead of breaking down.
Q2. Give any two ways in which biodegradable substances would affect the environment.
(i) While decomposing, they can release foul-smelling and sometimes harmful gases (like methane), causing air pollution and providing a breeding ground for disease-carrying insects. (ii) If generated faster than decomposers can break them down, they still accumulate temporarily and can deplete oxygen in water bodies as microorganisms multiply to consume them.
Q3. Give any two ways in which non-biodegradable substances would affect the environment.
(i) They accumulate in soil and water indefinitely, causing long-term pollution and reducing soil fertility. (ii) Certain non-biodegradable chemicals (like pesticides such as DDT) enter the food chain and undergo biological magnification, reaching harmful concentrations in top-level consumers.
Q4. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
A trophic level is each successive step in a food chain at which the transfer of food energy takes place. Example: Grass → Grasshopper → Frog → Snake → Hawk. Grass (a producer) is trophic level I; the grasshopper (herbivore, primary consumer) is trophic level II; the frog (primary carnivore, secondary consumer) is trophic level III; the snake (secondary carnivore) is trophic level IV; the hawk (top carnivore) is trophic level V.
Q5. What is the role of decomposers in the ecosystem?
Decomposers (bacteria and fungi) break down the complex organic compounds in dead plants, dead animals and waste products into simpler inorganic substances, which are returned to the soil, water and air. This recycles nutrients back to producers and prevents dead organic matter from piling up — making decomposers essential to the cycling of materials in the biosphere.
Q6. (MCQ) Which of the following groups contain only biodegradable items? (a) Grass, flowers and leather (b) Grass, wood and plastic (c) Fruit-peels, cake and lime-juice (d) Cake, wood and grass
Leather (tanned with chemicals) and plastic are non-biodegradable, ruling out (a) and (b).
Answer: (c) and (d) — fruit-peels, cake, lime-juice, wood and grass are all naturally biodegradable.
Q7. (MCQ) Which of the following constitute a food chain? (a) Grass, wheat and mango (b) Grass, goat and human (c) Goat, cow and elephant (d) Grass, fish and goat
A food chain needs a feeding sequence: a producer eaten by a consumer, eaten by a further consumer. Only option (b) shows this — grass (producer) is eaten by a goat (herbivore), which can be eaten by a human (omnivore/consumer).
Answer: (b).
Q8. (MCQ) Which of the following are environment-friendly practices? (a) Carrying cloth bags to put purchases in while shopping (b) Switching off unnecessary lights and fans (c) Walking to school instead of getting your mother to drop you on her scooter (d) All of the above
Answer: (d) All of the above — each reduces resource use or pollution (less plastic waste, less electricity consumption, less fuel burnt).
Q9. What will happen if we kill all the organisms in one trophic level?
The flow of food energy to the next (higher) trophic level stops, since that level no longer has a food source. At the same time, the level below the one removed loses its natural predator/consumer and can grow unchecked, disturbing population balance throughout the food chain and destabilising the ecosystem.
Q10. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Yes, the impact differs by level, and no level can be removed safely. Removing producers collapses the entire chain above them (herbivores starve or migrate). Removing herbivores lets producers grow unchecked while carnivores starve. Removing carnivores lets herbivore populations explode, over-consuming producers. Removing decomposers stops the breakdown of dead matter and nutrient recycling entirely, reducing soil fertility over time. Every trophic level is necessary to keep the ecosystem in balance.
Q11. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Biological magnification is the progressive increase in the concentration of a harmful, non-biodegradable chemical (like DDT) at each successive trophic level of a food chain, because the chemical isn’t excreted or broken down and instead accumulates in body tissue. Yes — the concentration is lowest at the producer level and highest at the topmost (tertiary) consumer level, since each level eats many organisms of the level below and inherits all their accumulated chemical load.
Q12. What are the problems caused by the non-biodegradable wastes that we generate?
They do not break down and keep accumulating in the environment, creating a growing disposal problem; some (heavy metals, pesticides) enter food chains and biomagnify, harming organisms at higher trophic levels; they pollute soil, water and air, and can alter soil pH and reduce fertility; and they can choke drains, waterways and harm wildlife that ingests them.
Q13. If all the waste we generate is biodegradable, will this have no impact on the environment?
No, it would still have an impact. Even biodegradable waste, if generated faster than decomposers can process it, releases foul-smelling and sometimes harmful gases (like methane, a greenhouse gas) as it decomposes, and provides a breeding ground for disease-causing organisms. So while biodegradable waste is far less persistent and damaging than non-biodegradable waste, it is not impact-free.
Q14. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
The ozone (O₃) layer in the upper atmosphere absorbs most of the Sun’s harmful ultraviolet (UV) radiation, preventing it from reaching the Earth’s surface. UV radiation can cause skin cancer and cataracts in humans, and damages crops and aquatic ecosystems (especially plankton). Ozone depletion is caused mainly by chlorofluorocarbons (CFCs), once widely used in refrigerants, air conditioners and aerosol sprays. Steps taken to limit the damage include international agreements (such as the Montreal Protocol, coordinated through UNEP, the United Nations Environment Programme) that phased out CFC production, and a shift to CFC-free refrigerants and technologies.
Q15. What is ozone and how does it affect any ecosystem?
Ozone is a molecule made of three oxygen atoms (O₃), formed naturally in the upper atmosphere (stratosphere) when UV radiation acts on oxygen molecules. At ground level it is a harmful pollutant, but in the stratosphere it forms a protective layer that absorbs most incoming solar UV radiation, shielding living organisms from UV-related damage such as skin cancer, cataracts, and disruption of photosynthesis and plankton populations in aquatic ecosystems.
Q16. How can you help in reducing the problem of waste disposal? Give any two methods.
(i) Practise the 3 Rs — reduce consumption, reuse items wherever possible, and recycle materials like paper, glass, metal and plastic instead of discarding them. (ii) Segregate biodegradable and non-biodegradable waste at the source (separate bins), so biodegradable waste can be composted and non-biodegradable waste can be recycled or safely disposed of, instead of both ending up mixed in a landfill.
Why This Chapter Matters for Boards
Our Environment is a short but reliably scoring chapter — reasoning-based questions on food chains, biological magnification, decomposers and the ozone layer appear almost every year in the CBSE board paper, often as 2–3 mark short-answer questions rather than numericals, making it one of the highest marks-per-minute-of-study chapters in Class 10 Science.
Extra Questions (HOTS) | Revision Notes | Formulas Handbook | Class 10 Science Book
CBSE Exam Weightage
This chapter falls under Unit V: Natural Resources in the CBSE Class 10 Science board exam syllabus. This unit typically carries around 5 marks (6.25%) of the 80-mark theory paper, based on CBSE’s published unit-wise weightage (Question Paper Design). CBSE sets weightage at the unit level rather than chapter-by-chapter, so the exact share can vary a little between years and sample papers.
Class 10 Science Chapter 13 – Notes and Extra Questions
Along with these NCERT Solutions, students can also use the Class 10 Science Chapter 13 Extra Questions and Class 10 Science Chapter 13 Revision Notes for quick revision and extra practice.
Frequently Asked Questions
Is this Chapter 13 or Chapter 15?
It’s Chapter 13 in the current 2026-27 rationalised NCERT book. It was Chapter 15 in the pre-2023 edition, before Periodic Classification of Elements, Sources of Energy and Management of Natural Resources were removed from the Class 10 syllabus and the remaining chapters shifted down in number.
How many exercise questions does this chapter have?
16 end-of-chapter exercise questions, matching the current 2026-27 rationalised NCERT textbook.
