Chapter 13 · CBSE Board 2027
Our Environment Class 10 important questions with answers
The 10 questions to practise first, picked from every CBSE board paper 2023–2026. Each one has the official answer and how to write it for full marks. Then try the free 10-question test.
What comes in the exam
- Our Environment is in the Natural Resources unit, worth 5 marks.
- MCQs come most, then 3-mark questions, Assertion–Reason and 2-mark questions.
- There are no case studies or 5-mark questions here.
- Almost every year you get biological magnification, the 10 per cent law with energy at each trophic level, food chains, and biodegradable versus non-biodegradable waste.
- The ozone layer, decomposers and food webs also come almost every year.
- One-way flow of energy and the parts of an ecosystem come almost every year too, mostly as MCQs, AR or short answers.
- The effects of our waste and managing garbage come often.
Top 10 Our Environment questions from board papers
Real CBSE questions, printed as they appeared. Open each answer to see the marking and the steps.
- Q1 Assertion–Reason · 1 mark CBSE · 2026
Numbers at lower trophic levels
Assertion (A): There are generally a greater number of individuals at the lower trophic levels of an ecosystem. Reason (R): The greatest number is of the producers.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Write your answer, send a photo, get it marked in DheeAnswer and marking
Correct option: (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- Check A: lower trophic levels have more individuals. A is true
- Check R: producers are the most numerous. R is true
- The reason is more energy at lower levels; R only restates a fact. R does not explain A ⇒ option (B) 1 mark
Answer: (B) Both A and R are true, but R is not the correct explanation of A.
Marks: Correct option 1
For full marks: Ask whether R gives the cause: the cause is more energy at lower levels (10% law).
Where students lose marks: Picking (A): R agrees with A, but it repeats a fact instead of giving the reason.
CBSE marking scheme
Both true; more individuals at lower levels is due to more energy available there (10% law), not merely because producers are most numerous, so R does not explain A.
- Q2 MCQ · 1 mark CBSE · 2026
Predators feeding on many types
Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level form the:
- (A) Food web
- (B) Ecosystem
- (C) Ecological pyramid
- (D) Food chain
Write your answer, send a photo, get it marked in DheeAnswer and marking
Correct option: (A) Food web
- When animals eat many kinds of food, many food chains join together. Many connected food chains
- Connected food chains form a food web. Food web ⇒ option (A) 1 mark
Answer: (A) Food web
Marks: Correct option 1
For full marks: A food chain is one straight path; a food web is many chains linked together.
Where students lose marks: Picking (D): a food chain is a single path, not several types of food.
CBSE marking scheme
Organisms feeding on several kinds of organisms create many interconnected food chains, forming a food web.
- Q3 MCQ · 1 mark CBSE · 2026
What limits trophic levels
Which of the following limits the number of trophic levels in a food chain?
- (A) Availability of water
- (B) Deficient food supply
- (C) Decrease in energy at higher levels
- (D) Pollution in air
Write your answer, send a photo, get it marked in DheeAnswer and marking
Correct option: (C) Decrease in energy at higher levels
- Only about 10% of energy passes on to the next trophic level. 10% law
- After 3 or 4 levels too little energy is left. Energy decreases at higher levels ⇒ option (C) 1 mark
Answer: (C) Decrease in energy at higher levels
Marks: Correct option 1
For full marks: Write the 10% law: only one tenth of the energy reaches the next level.
Where students lose marks: Picking (B): food supply seems the limit, but the real cause is the energy lost at each level.
CBSE marking scheme
Only about 10% of energy passes to each next level, so too little energy remains after 3-4 levels.
- Q4 MCQ · 1 mark CBSE · 2026
Pick the correct food chain
Examine the given food chains to establish the correct one in an ecosystem:
- (A) Seed → mouse → snake → deer
- (B) Algae → small fish → large fish → hawk
- (C) Grasshopper → frog → snake → elephant
- (D) Plants → rabbit → deer → wolf
Write your answer, send a photo, get it marked in DheeAnswer and marking
Correct option: (B) Algae → small fish → large fish → hawk
- A food chain starts with a producer, and each animal eats the one before it. Producer → herbivore → carnivore
- Check each: a deer does not eat snakes, an elephant does not eat snakes, a deer does not eat rabbits. (A), (C), (D) are wrong
- Only one chain has each living thing eaten by the next one. Algae → small fish → large fish → hawk ⇒ option (B) 1 mark
Answer: (B) Algae → small fish → large fish → hawk
Marks: Correct option 1
For full marks: Check every arrow: does the next animal really eat the one before?
Where students lose marks: Picking (D): it starts with plants, but a deer does not eat rabbits.
CBSE marking scheme
A food chain starts with a producer and each consumer eats the one before: algae → small fish → large fish → hawk.
- Q5 Very short answer · 2 marks CBSE · 2024
Term for unbreakable materials
Name the term used for the materials which cannot be broken down by biological processes. Give two ways by which they harm various components of an ecosystem.
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- Name the materials that microbes cannot break down. Non-biodegradable substances 1 mark
- Give the first harm they cause. They are inert and persist long in the environment, causing pollution. 0.5 marks
- Give a second harm. They cause biological magnification (or affect soil fertility). 0.5 marks
Answer: Non-biodegradable substances; they persist and pollute, and cause biological magnification
Marks: Term 1 · Two harms 1
For full marks: Give two separate harms, like 'persist long, causing pollution' and 'biological magnification'; each is a half mark.
Where students lose marks: Writing 'biodegradable' for the term; materials that cannot be broken down are non-biodegradable.
CBSE marking scheme
Non-biodegradable substances (1). Any two (½ each): they are inert and persist long in the environment causing pollution; they cause biological magnification; they affect soil fertility (or any other).
- Q6 Very short answer · 2 marks CBSE · 2023
Cloth bags; urban waste disposal
(a) State any one advantage of using cloth bags over plastic bags. (b) List any two methods by which the solid wastes generated in urban areas can be safely disposed off.
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- (a) Think of what happens to a cloth bag when thrown away. Cloth bag is biodegradable (eco-friendly). 1 mark
- (b) Give two safe ways to deal with city waste. Any two: segregation of biodegradable and non-biodegradable waste at source ; composting ; recycling 1 mark
Answer: (a) Biodegradable; (b) segregation at source, composting (or recycling)
Marks: Advantage 1 · Two methods 1
For full marks: In (b) name two separate methods, like 'segregation at source' and 'composting'; each earns half a mark.
Where students lose marks: Writing 'cloth bags are stronger' or 'cheaper' in (a); the advantage that earns the mark is that cloth is biodegradable.
CBSE marking scheme
(a) Cloth bag is biodegradable / eco-friendly (1). (b) Any two: segregation of biodegradable and non-biodegradable waste at source; composting; recycling (½ + ½).
- Q7 Short answer · 3 marks CBSE · 2023
Harmful chemicals in food chain
Explain how some harmful chemicals enter our bodies through the food chain. Why is the concentration of these harmful chemicals found to be maximum in human beings?
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- Follow the pesticide from the field to your plate. Pesticides used on crops wash into soil and water ; they are absorbed by plants with water and minerals and by aquatic animals ; eating these foods brings them into our body 2 marks
- Think of where humans sit in the food chain. Humans are at the top level of food chains, so the non-degradable chemicals accumulate most in us: biological magnification. 1 mark
Answer: Pesticides enter via soil, water, plants and animals we eat; maximum in humans due to biological magnification
Marks: Entry into body 2 · Reason for maximum 1
For full marks: Name 'biological magnification' and say humans are at the top level; both belong in the last mark.
Where students lose marks: Saying humans get the most chemicals because they eat the most food; the reason is their top trophic level.
CBSE marking scheme
Pesticides used on crops wash into soil and water, are absorbed by plants with water and minerals and by aquatic animals; eating these foods brings them into our body (2). Humans occupy the top level of food chains, so the non-degradable chemicals accumulate maximally in us - biological magnification (1).
- Q8 Short answer · 3 marks CBSE · 2026
Waste, crop fields, pesticides
(a) Improper waste disposal is a curse to the environment. Explain. (b) Why are crop fields considered as artificial ecosystems ? (c) Farmers are using pesticides on the crop plants, but the chances of accumulation of harmful chemicals is greatest in human beings. Why ? Name the phenomenon.
Write your answer, send a photo, get it marked in DheeAnswer and marking
- (a) Think of what happens to waste that is not separated or broken down. Unsegregated waste accumulates ; plastics are not biodegraded, clog drains, pollute rivers and oceans and harm cattle, fish etc. 1 mark
- (b) Say who made a crop field and what still happens inside it. Crop fields are man-made, yet their living organisms interact with each other and with abiotic components. 1 mark
- (c) Think of where humans sit in the food chain. Pesticides are non-biodegradable and accumulate at each trophic level ; humans are at the top level, so the concentration is maximum in them 0.5 marks
- Give the name of this build-up. Biological magnification 0.5 marks
Answer: (a) Waste piles up, clogs drains, pollutes water, harms animals; (b) man-made but living and non-living parts interact; (c) biological magnification
Marks: Waste 1 · Crop field 1 · Reason ½ · Name ½
For full marks: In (c) write the name 'biological magnification' as its own line; it is a separate half mark.
Where students lose marks: In (b) saying only 'man-made' and not that its organisms interact with abiotic parts, which is what makes it an ecosystem.
CBSE marking scheme
(a) Unsegregated waste accumulates; plastics are not biodegraded, clog drains, pollute rivers and oceans and harm cattle, fish etc. (1). (b) Crop fields are man-made, yet their living organisms interact with each other and with abiotic components (1). (c) Pesticides are non-biodegradable and accumulate progressively at each trophic level; humans occupy the top level so the concentration is maximum in them (½); biological magnification (½).
- Q9 Short answer · 3 marks CBSE · 2026
Plastic bags; paddy field runoff
(a) Mention any one harmful effect of using plastic bags on the environment. Suggest better alternatives to the usage of plastic bags. (b) Paddy fields require a large amount of water. The pesticides and chemical fertilizers used are washed down into the soil or waterbodies. How do these chemicals reach our bodies ? What is this phenomenon known as ?
Write your answer, send a photo, get it marked in DheeAnswer and marking
- (a) Give one harm, linked to why plastic never goes away. Plastics are non-biodegradable and persist in the environment for a long time 0.5 marks
- Suggest a bag that can be reused or will decompose. Alternative: jute bag or cloth bag 0.5 marks
- (b) Trace the chemicals from the field, up through the food chain, to us. The chemicals are not biodegradable ; they are absorbed by plants and animals and accumulate progressively at each trophic level ; humans at the top get the maximum concentration 1 mark
- Now name the process you just described. Biological magnification 1 mark
Answer: (a) Plastics are non-biodegradable and persist; use jute or cloth bags (b) Through the food chain, building up at each level — biological magnification
Marks: Harm ½ · Alternative ½ · How they reach us 1 · Name 1
For full marks: In (b) write 'accumulate progressively at each trophic level' and 'humans at the top get the maximum' — together they earn the full mark.
Where students lose marks: In (b) naming biological magnification but not explaining how the chemicals pass up the food chain, which loses a full mark.
CBSE marking scheme
(a) Plastics are non-biodegradable and persist in the environment for long (½); alternative - jute or cloth bag (½). (b) These chemicals are not biodegradable, get absorbed by plants/animals and accumulate progressively at each trophic level; humans at the top get the maximum concentration (1). Phenomenon: biological magnification (1).
- Q10 Short answer · 3 marks CBSE · 2025
One-way energy; 10,000 J
(a) "In a food chain energy flow is unidirectional." Give two reasons for the given statement. (b) If 10,000 J energy is available at the producer level, how much energy will be available to the secondary consumers? Give reason to justify your answer.
Write your answer, send a photo, get it marked in DheeAnswer and marking
- (a) Think of whether energy can go back to the level it came from. Any two: energy captured by autotrophs does not revert to the solar input, nor does herbivores' energy go back to autotrophs ; energy passed on is no longer available to the previous level ; energy diminishes at each level 2 marks
- (b) Secondary consumers are two levels above the producers. 100 J 0.5 marks
- Only 10% passes on at each step, so take 10% twice. 10000 J → 1000 J → 100 J by the 10% law 0.5 marks
Answer: (a) Energy never returns to the earlier level; (b) 100 J by the 10% law
Marks: Two reasons 2 · Energy ½ · Reason ½
For full marks: Write the chain 10000 → 1000 → 100 J with 'the 10% law'; the reason is half of (b).
Where students lose marks: Giving 1000 J; that is the energy at the herbivores, one level up, not at the secondary consumers.
CBSE marking scheme
(a) Any two: energy captured by autotrophs never reverts to solar input, nor herbivores' energy to autotrophs; energy passed on is no longer available to the previous level; energy diminishes at each level (1×2). (b) 100 J (½); 10000 → 1000 → 100 J by the 10% law (½).
Free 10-question test: Our Environment
MCQ and Assertion–Reason questions from CBSE papers. About 10 minutes. Your score shows straight away.
Common mistakes in Our Environment
Mistake Explaining biological magnification without the reason it happens.
Fix Say the chemicals are non-biodegradable, so they build up at each trophic level. Humans are at the top, so they get the most. Then name the phenomenon on its own line: it carries its own mark.
Mistake Skipping steps in how pesticides reach our body.
Fix Give the full path: sprayed on crops, washed into soil and water, taken up by plants with water and minerals and by water animals, then eaten by us. In a 3-mark answer the scheme gives 2 marks for this path.
Mistake Counting levels wrongly in a 10 per cent law sum.
Fix Producers are the first level. Herbivores are the second level. Secondary consumers are the third. Divide by 10 at each step and show every step with J.
Mistake Writing a food chain in the wrong order.
Fix Start with a producer (a plant or algae). Each animal eats the one before it, and the arrow points from the food to the eater. Count trophic levels from the producer.
Mistake Guessing in biodegradable questions.
Fix Ask: can bacteria and fungi break it down? Things made from living matter, like paper, cotton, wool and leather, can. Plastics and polythene cannot.
Mistake In Assertion–Reason, picking 'R explains A' because both are true.
Fix Check A and R on their own first. Then ask: does R give the cause of A? If R is a true fact about something else, it does not explain A.
How to write for full marks
- Use the key words in definitions: biological magnification is the progressive build-up of non-biodegradable chemicals at each higher trophic level.
- For decomposers, write a one-line definition (they break down complex organic matter into simple substances), two examples (bacteria, fungi) for ½ mark each, and how they return nutrients to the soil.
- For energy sums, write the levels with arrows and units, like 'producer 10,000 J → herbivore … J → …', and give the 10 per cent law as the reason.
- For 'why is energy flow one-way', give two separate reasons: energy never goes back to the level before, and energy keeps getting less at each level. Each reason carries 1 mark.
- For plastic questions, give one clear harm (it is non-biodegradable and stays for a long time) and a named alternative such as a jute or cloth bag. Each part carries ½ mark.
Not in the 2026-27 exam
Leave these out of your revision.
- Information in the NCERT boxes
Questions students ask
Which Our Environment questions are most important for the Class 10 board exam 2027?
Expect MCQs and AR on food chains, the 10 per cent law, ozone and waste, and 3-mark questions on biological magnification and energy flow. The 10 questions on this page are real CBSE board questions from 2023–2026, chosen across the chapter's topics and question types.
How many marks does Our Environment carry in the Class 10 board exam?
Our Environment is part of the Natural Resources unit, which carries 5 of the 80 theory marks in the CBSE Class 10 Science paper.
Are these real CBSE previous year questions?
Yes. Each question is printed as it appeared in a CBSE board paper or sample paper, with its source, and the answer follows CBSE's official marking scheme.
Questions and answers: CBSE board papers, sample papers and official marking schemes, 2023–2026. Worked steps and tips: Dhee.