Our Environment is Chapter 13 of Class 10 NCERT Science (Reprint 2026-27). It covers how living and non-living components interact within an ecosystem, how energy flows through food chains, and how human activities damage the environment through ozone depletion and waste mismanagement.
Important questions class 10 science chapter 13 on this page cover every exam-relevant topic: MCQs, very short answer questions, short answer questions, long answer questions, extra questions, and previous year question patterns. All questions follow the NCERT chapter structure and the CBSE 2026 syllabus.
This chapter carries consistent board weightage across 1-mark, 3-mark, and 5-mark questions. A student who understands why food chains are limited to 3 or 4 steps and why top carnivores carry the highest pesticide load will handle every question type with confidence. All questions and answers are available section by section below. For Chapter 12, visit Important Questions Class 10 Science Chapter 12. For Chapter 14, visit Important Questions Class 10 Science Chapter 14.
Key Takeaways
| Topic |
What to Know |
| Ecosystem |
Biotic + abiotic components interacting together |
| Producers |
Green plants that fix solar energy via photosynthesis |
| Consumers |
Herbivores, carnivores, omnivores feeding on producers or other consumers |
| Decomposers |
Bacteria and fungi that break complex organic matter into simple inorganic substances |
| Trophic Level |
Each step in a food chain |
| 10% Law |
Only 10% of energy transfers from one trophic level to the next |
| Biological Magnification |
Progressive accumulation of non-degradable chemicals up the food chain |
| Ozone |
O3 molecule that shields Earth from UV radiation; depleted by CFCs |
| Biodegradable |
Broken down by biological processes |
| Non-Biodegradable |
Persists in environment; cannot be broken down biologically |
Introduction to Class 10 Science Chapter 13 Our Environment
Three concepts carry the most board marks in this chapter. First, the 10% law: only about 10% of the energy at one trophic level reaches the next. Second, biological magnification: non-degradable chemicals accumulate in higher concentrations at higher trophic levels. Third, ozone depletion: CFCs break down ozone, removing Earth's UV shield.
Understanding why food chains are limited to 3 or 4 steps, and why top carnivores carry the highest pesticide load, matters more than memorising definitions alone. These are the questions that appear as 3-mark and 5-mark items in CBSE 2026 board exams.
Use these questions alongside NCERT Solutions Class 10 Science Chapter 13 for textbook-level accuracy in your answers.
Important Topics in Our Environment Class 10
Every board question from this chapter maps to one of these seven areas. These our environment class 10 notes cover the essential chapter structure before you start practising questions.
Ecosystem and its components: An ecosystem includes all interacting organisms in an area along with non-living physical factors. Biotic components are producers, consumers, and decomposers. Abiotic components include temperature, rainfall, wind, soil, and minerals.
Food chains and food webs: A food chain is a series of organisms where each feeds on the one before it. A food web is a network of interconnected food chains. Food webs are more realistic because most organisms are part of multiple chains.
Trophic levels: Each step in a food chain is a trophic level. Producers are at the first trophic level. Herbivores are at the second. Small carnivores are at the third. Larger carnivores are at the fourth.
10% law of energy transfer: About 10% of the organic matter at each trophic level reaches the next level. The rest is lost as heat, used in digestion, or used for metabolic work. This is why food chains generally have only 3 or 4 trophic levels.
Biological magnification: Non-degradable chemicals like pesticides enter the food chain through soil and water. They do not break down and accumulate progressively at each trophic level. Human beings, sitting at the top of most food chains, end up with the highest concentration.
Ozone layer depletion: Ozone (O3) forms in the upper atmosphere when UV radiation splits O2 molecules. Synthetic chemicals called CFCs, used in refrigerants and fire extinguishers, break down ozone. In 1987, the UNEP forged an agreement to freeze CFC production at 1986 levels.
Biodegradable and non-biodegradable waste: Biodegradable substances break down through biological processes. Non-biodegradable substances persist in the environment. Many human-made materials like plastics are non-biodegradable because bacteria lack the enzymes to break them down.
Our Environment Class 10 MCQs with Answers
These 1-mark questions test core definitions and concepts directly from the NCERT chapter. These our environment class 10 questions and answers cover the MCQ format that appears in CBSE 2026 board papers.
Q1. Which of the following groups contain only biodegradable items? (a) Grass, wood and plastic (b) Fruit-peels, cake and lime-juice (c) Grass, flowers and leather (d) Both (b) and (c) Answer: (d) Both (b) and (c).
Q2. Which of the following constitutes a correct food chain? (a) Grass, wheat and mango (b) Goat, cow and elephant (c) Grass, goat and human (d) Grass, fish and goat Answer: (c) Grass, goat and human.
Q3. The flow of energy in an ecosystem is: (a) Bidirectional (b) Cyclic (c) Unidirectional (d) Multidirectional Answer: (c) Unidirectional.
Q4. The phenomenon of progressive increase in concentration of non-degradable substances at each trophic level is called: (a) Food web (b) Biomagnification (c) Decomposition (d) Eutrophication Answer: (b) Biomagnification.
Q5. Ozone layer depletion is mainly caused by: (a) Carbon dioxide (b) Sulphur dioxide (c) Chlorofluorocarbons (d) Methane Answer: (c) Chlorofluorocarbons.
Q6. Which organisms are at the first trophic level in a food chain? (a) Herbivores (b) Decomposers (c) Carnivores (d) Producers Answer: (d) Producers.
Q7. Only about what percentage of energy is transferred from one trophic level to the next? (a) 1% (b) 5% (c) 10% (d) 20% Answer: (c) 10%.
Q8. Which of the following is a non-biodegradable substance? (a) Paper (b) Wood (c) Plastic (d) Cotton Answer: (c) Plastic.
Very Short Answer Questions from Our Environment
These 1-mark questions cover definitions that students must know precisely. These important questions of our environment class 10 appear as direct-recall items in board papers every year.
Q9. What is a trophic level? Each step or level of a food chain is called a trophic level. Producers form the first, herbivores the second, and carnivores form higher trophic levels.
Q10. Name the two components of an ecosystem. Biotic components (living organisms) and abiotic components (physical factors like temperature, soil, water, and minerals).
Q11. What is biological magnification? Biological magnification is the progressive accumulation of non-degradable chemicals at each successive trophic level in a food chain, reaching the highest concentration in top consumers.
Q12. What is ozone? Write its molecular formula. Ozone is a molecule composed of three atoms of oxygen. Its molecular formula is O3.
Q13. Name two substances that cause ozone layer depletion. Chlorofluorocarbons (CFCs) used in refrigerants and fire extinguishers are the primary cause of ozone layer depletion.
Q14. Define biodegradable substances. Substances that can be broken down into simpler forms by biological processes, mainly through the action of bacteria and fungi, are called biodegradable substances.
Q15. What is a food web? A food web is a network of interconnected food chains where each organism may be part of more than one food chain in an ecosystem.
Short Answer Questions on Food Chains, Food Webs and Trophic Levels
Board exams frequently ask 2-mark and 3-mark questions on energy flow and food chain structure. These our environment class 10 questions and answers are drawn from the NCERT chapter pages 210-212, Reprint 2026-27.
Q16. What are trophic levels? Give an example of a food chain and state the different trophic levels in it. Each step or level in a food chain is a trophic level. Example: Grass → Grasshopper → Frog → Snake → Eagle. Grass: first trophic level (producer). Grasshopper: second (primary consumer). Frog: third (secondary consumer). Snake: fourth (tertiary consumer). Eagle: fifth (top carnivore).
Q17. Why do food chains generally consist of only three or four steps? Only about 10% of energy at one trophic level reaches the next. Energy loss at each step is so large that very little usable energy remains after four trophic levels. An organism at the fifth or sixth level would receive insufficient energy for survival.
Q18. Explain why the flow of energy in an ecosystem is unidirectional. Energy captured by producers from sunlight does not return to the sun. Energy passed to herbivores does not return to producers. At each level, energy is lost as heat and cannot be reused. This makes the flow strictly one-directional.
Q19. Why is a food web considered more realistic than a simple food chain? In nature, most organisms feed on more than one type of organism and are eaten by more than one predator. A food web captures these multiple feeding relationships. A simple food chain shows only one pathway and does not represent real ecosystem complexity.
Q20. What is the role of decomposers in the ecosystem? Decomposers, mainly bacteria and fungi, break down the dead remains and waste products of organisms. They convert complex organic substances into simple inorganic substances that go back into the soil. This replenishes nutrients for producers and maintains the nutrient cycle.
Short Answer Questions on Ozone Layer and Waste Management
These our environment class 10 extra questions and answers cover the second half of the NCERT chapter, which carries consistent 3-mark and 5-mark board marks.
Q21. What is ozone and how does it affect any ecosystem? Ozone (O3) is a molecule of three oxygen atoms found in the upper atmosphere. It shields Earth's surface from harmful ultraviolet radiation. UV radiation damages DNA, causes skin cancer, and harms crops. Without the ozone layer, these harmful rays would directly reach Earth's surface and damage all life forms.
Q22. Why are some substances biodegradable and some non-biodegradable? Decomposers have specific enzymes that break down naturally occurring substances like paper, wood, and food. They do not have enzymes to break down many human-made materials like plastics. These materials resist biological breakdown and persist in the environment.
Q23. Give any two ways in which non-biodegradable substances affect the environment. First, they accumulate in the environment for long periods and cause land and water pollution. Second, they enter food chains and undergo biological magnification, reaching dangerous concentrations in top consumers including humans.
Q24. Give any two ways in which biodegradable substances affect the environment. First, large accumulations of biodegradable waste generate harmful gases during decomposition, causing air pollution. Second, excess biodegradable waste provides breeding grounds for flies and mosquitoes, which spread diseases like malaria and cholera.
Q25. How can you help in reducing the problem of waste disposal? Give any two methods. First, practise the 3Rs: Reduce waste generation, Reuse materials wherever possible, and Recycle substances like paper and plastic. Second, separate biodegradable and non-biodegradable waste at the source so each type can be handled appropriately.
Long Answer Questions on Our Environment Class 10
These 4-mark and 5-mark questions require structured, step-by-step answers. These our environment class 10 important questions appear consistently in CBSE 2026 board papers.
Q26. What will happen if we kill all organisms in one trophic level? Will the impact be different for different trophic levels? Removing any trophic level disturbs the balance of the entire ecosystem. If producers are removed, all consumers and decomposers lose their food source and the entire ecosystem collapses.
If herbivores are removed, carnivores lose food and die, while producer populations increase uncontrollably. If carnivores are removed, herbivore populations explode, leading to overgrazing and destruction of the producer level.
The impact differs at different levels, but no trophic level can be removed without causing damage. Removing producers causes total ecosystem collapse. Removing top carnivores causes imbalance through unchecked herbivore growth.
Q27. What is biological magnification? Will levels of magnification be different at different levels of the ecosystem? Biological magnification is the progressive accumulation of non-degradable harmful chemicals at increasing concentrations as you move up each trophic level. These chemicals enter the food chain from soil and water, absorbed by plants and aquatic organisms. They are not broken down and keep accumulating in the bodies of consumers.
Yes, magnification levels differ at different trophic levels. The concentration is lowest at the producer level and increases at each successive level. Human beings and other top carnivores carry the highest concentrations.
Q28. Why is damage to the ozone layer a cause for concern? What steps have been taken to limit this damage? The ozone layer shields Earth from ultraviolet radiation. UV radiation causes skin cancer and eye cataracts in humans, reduces crop productivity, and harms aquatic ecosystems by damaging phytoplankton.
Ozone began depleting sharply in the 1980s due to CFCs released from refrigerants and fire extinguishers. In 1987, the UNEP forged an agreement to freeze CFC production at 1986 levels. It is now mandatory for all manufacturing companies worldwide to produce CFC-free refrigerators.
Our Environment Class 10 Extra Questions and Answers
These questions go beyond the standard NCERT exercises and test inference and application. These our environment class 10 extra questions and answers appear in pre-board and unit tests for CBSE 2026.
Q29. An aquarium requires regular cleaning whereas a lake or pond normally does not. Why? A lake has a large variety of organisms forming many food chains and a stable food web. This diversity allows the ecosystem to clean itself naturally through balanced decomposition and nutrient cycling. An aquarium has very few organisms, a limited number of food chains, and lacks sufficient decomposers for self-cleaning.
Q30. If all the waste we generate is biodegradable, will this have no impact on the environment? Even fully biodegradable waste causes environmental harm if generated in excess. Decomposers cannot process unlimited quantities at one time. Excess biodegradable waste releases harmful gases during decomposition and becomes a breeding ground for disease-causing organisms.
Q31. Give the correct sequence of trophic levels in a terrestrial food chain with an example. Producers (first) → Herbivores/Primary consumers (second) → Carnivores/Secondary consumers (third) → Larger carnivores/Tertiary consumers (fourth). Example: Grass → Deer → Fox → Lion.
Q32. Using the 10% law, calculate the energy available to the snake in the food chain: Grass (10,000 J) → Grasshopper → Frog → Snake. Grass = 10,000 J. Grasshopper gets 10% = 1,000 J. Frog gets 10% of 1,000 J = 100 J. Snake gets 10% of 100 J = 10 J.
Q33. Which of the following is not an environment-friendly practice and why? (a) Carrying cloth bags while shopping (b) Using plastic carry bags for every purchase (c) Switching off unnecessary lights (b) Using plastic carry bags is not environment-friendly. Plastic is non-biodegradable and persists in the environment for decades. It pollutes land and water and cannot be broken down by decomposers.
Our Environment Class 10 PYQ: Previous Year Questions
These our environment previous year questions class 10 reflect actual board exam patterns. Practising our environment class 10 pyq questions tells you exactly what the examiner expects in terms of format, length, and accuracy.
Q34. (Board-style 3 marks) What are trophic levels? Why does the number of trophic levels in a food chain rarely exceed four? Each step or level in a food chain is a trophic level. Producers form the first, herbivores the second, and carnivores form higher levels. The number rarely exceeds four because of the 10% law: only 10% of energy at one trophic level transfers to the next. By the fourth trophic level, the usable energy remaining is too small to sustain a population at the fifth level.
Q35. (Board-style 3 marks) DDT sprayed in small amounts on food plants was detected in high concentrations in human bodies. Explain how this happened. This occurred through biological magnification. DDT entered the soil after spraying. Plants absorbed it with water and minerals. Herbivores eating the plants accumulated a higher concentration. Carnivores eating the herbivores accumulated an even higher concentration. Since humans occupy the top level in most food chains, the maximum concentration of DDT accumulated in human bodies.
Q36. (Board-style 5 marks) Draw a labelled diagram showing the flow of energy through trophic levels in an ecosystem. Explain why energy flow is unidirectional. Sunlight → Producers (1st trophic level) → Herbivores (2nd trophic level) → Carnivores (3rd trophic level) → Top Carnivores (4th trophic level), with energy lost as heat at each step.
Energy flow is unidirectional because the energy captured by producers from sunlight does not return to the sun. Energy that passes to herbivores cannot return to producers. At every level, energy is lost as heat during metabolic processes and cannot be recycled. This makes the flow strictly one-directional, unlike the cyclic flow of matter.
Q37. (Board-style 2 marks) Explain the significance of decomposers in the ecosystem. Decomposers break down complex organic substances in dead organisms into simple inorganic substances that return to the soil. This replenishes nutrients for producers and maintains the nutrient cycle. Without decomposers, dead organic matter would pile up and producers would eventually be unable to sustain the ecosystem.
Case-Based and Reason-Based Questions from Our Environment
Q38. A student found that fish in a lake contained 10 times more pesticide than the water. What explains this, and which organism in the food chain would have the highest pesticide concentration? This is biological magnification. Pesticides in water are absorbed by aquatic plants and small organisms. Fish eating these organisms accumulate higher concentrations. The organism at the top of the food chain: a large predatory fish or a bird eating the fish, would have the highest pesticide concentration.
Q39. Kulhads (clay cups) were suggested as a replacement for plastic cups in trains. But the idea was dropped. Give one scientific and one environmental reason. Scientific reason: Kulhads are biodegradable, which is better than plastic. Environmental reason: Making kulhads on a large scale requires digging clay from the topsoil. This leads to loss of fertile topsoil, damaging agricultural land.
Q40. A food chain has 5 trophic levels and 10,000 J of energy at the producer level. How much energy reaches the 5th trophic level? What does this tell you about long food chains? Producer = 10,000 J → 2nd level = 1,000 J → 3rd level = 100 J → 4th level = 10 J → 5th level = 1 J. This shows that the energy available to top-level organisms is extremely small. Long food chains are energetically inefficient and unsustainable for populations at higher levels.
Most Important Questions from Our Environment for CBSE 2026 Exams
