---
title: "Our Environment: CBSE Class 10 Science previous year questions"
url: https://www.swavid.com/cbse/class-10/science/pyq/our-environment
---

# Our Environment: CBSE Class 10 Science previous year questions

16 questions from CBSE Class 10 board papers, newest first, each with full working.

## CBSE Class 10 Science Question Paper 2026 (Set 31/1/1) with Solutions

### Question 7

*1 mark · MCQ*

Which of the following group is not 'biodegradable' ?

- Vegetable peels, dead leaves, paper
- Cow dung, leather bag, water
- Polythene bag, rubber band, ball pen
- Paper, fruits, bones

**Solution**

1. Substances that are broken down by biological processes are called biodegradable.
2. Polythene bags, rubber bands, and ball pens cannot be broken down easily by microorganisms and are non-biodegradable.

**Answer:** (c) Polythene bag, rubber band, ball pen

> Common mistake: Confusing rubber with natural rubber products that might degrade slowly, while synthetic polymers and plastics are strictly non-biodegradable.

### Question 13

*3 marks · Short answer*

Given below is a pyramid showing various trophic levels in an ecosystem :
(iv) Tertiary consumers
(iii) Secondary consumers
(ii) Primary consumers
(i) Producers
(a) From the organisms listed below, identify which one is to be placed at which trophic level ?
Deer, Grass, Lion, Snake, Rabbit
(b) Discuss the reason why primary consumers will have more energy as compared to secondary consumers ?
(c) Why is the base of the pyramid broad ?

**Part (a)**

1. Producers: Grass
2. Primary consumers: Deer, Rabbit
3. Secondary consumers: Snake
4. Tertiary consumers: Lion

Answer (a): Producers: Grass; Primary consumers: Deer, Rabbit; Secondary consumers: Snake; Tertiary consumers: Lion.

**Part (b)**

1. According to the 10% law, only 10% of the energy is transferred to the next trophic level.
2. The rest of the energy is lost as heat to the environment during metabolic activities.

Answer (b): Primary consumers have more energy because energy is lost at each successive trophic level.

**Part (c)**

1. The base is broad because the number of producers is the highest in an ecosystem to support all other trophic levels.

Answer (c): The base is broad because producers are the most abundant organisms.

**Answer:** The trophic levels are organized based on energy flow and population size.

> Common mistake: Forgetting that energy decreases as we move up the trophic levels.

## CBSE Class 10 Science Question Paper 2025 (Set 31/1/1) with Solutions

### Question 15

*1 mark · MCQ*

Which of the following groups do not constitute a food chain ?
(i) Wolf, rabbit, grass, lion
(ii) Plankton, man, grasshopper, fish
(iii) Hawk, grass, snake, grasshopper, frog
(iv) Grass, snake, wolf, tiger

- (i) and (iv)
- (i) and (iii)
- (ii) and (iii)
- (ii) and (iv)

**Solution**

1. In group (ii), plankton, man, grasshopper, and fish do not form a linear trophic sequence because man does not eat plankton or grasshoppers directly in a standard chain.
2. In group (iv), grass, snake, wolf, and tiger do not form a correct food chain as snakes are not herbivores feeding on grass.

**Answer:** (d) (ii) and (iv)

> Common mistake: Failing to trace the correct trophic levels of organisms in the options.

### Question 16

*1 mark · MCQ*

The percentage of solar energy which is not converted into food energy by the leaves of green plants in a terrestrial ecosystem is about :

- 1%
- 10%
- 90%
- 99%

**Solution**

1. Green plants capture about $1\%$ of the solar energy that falls on their leaves and convert it into food energy.
2. Therefore, the percentage of solar energy which is not converted into food energy is $100\% - 1\% = 99\%$.

**Answer:** (d) 99%

> Common mistake: Confusing the $1\%$ energy captured by plants with the $10\%$ law of energy transfer between trophic levels.

### Question 20

*1 mark · Assertion and reason*

Assertion (A) : The amount of ozone in the atmosphere began to drop sharply in the 1980s.
Reason (R) : The oxygen atoms combine with molecular oxygen to form ozone.

- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Assertion (A) is false, but Reason (R) is true.

**Solution**

1. The amount of ozone in the atmosphere began to drop sharply in the 1980s mainly due to synthetic chemicals like chlorofluorocarbons (CFCs).
2. Higher up in the atmosphere, UV radiations split molecular oxygen into free oxygen atoms, which then combine with molecular oxygen to form ozone.
3. Both statements are true independently according to NCERT, but the formation of ozone does not explain why its amount dropped sharply in the 1980s.

**Answer:** Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

> Common mistake: Assuming the natural formation process of ozone explains its anthropogenic depletion.

### Question 26

*2 marks · Very short answer*

"Excessive use of chemicals and pesticides in agriculture adversely effect the environment." Justify this statement.

**Solution**

1. Excessive use of chemicals and pesticides leads to soil degradation by killing useful microorganisms and reducing natural fertility.
2. These non-biodegradable chemicals enter food chains and undergo biological magnification, harming higher trophic levels including humans.

**Answer:** Excessive use of chemicals degrades soil fertility by killing beneficial microbes and causes biological magnification of toxic substances in food chains.

> Common mistake: Writing general pollution effects instead of specific agricultural impacts like soil degradation and biological magnification.

## CBSE Class 10 Science Question Paper 2024 (Set 31/1/1) with Solutions

### Question 15

*1 mark · MCQ*

Identify the food chain in which the organisms of the second trophic level are missing :

- Grass, goat, lion
- Zooplankton, Phytoplankton, small fish, large fish
- Tiger, grass, snake, frog
- Grasshopper, grass, snake, frog, eagle

**Solution**

1. In the food chain 'Zooplankton, Phytoplankton, small fish, large fish', phytoplankton are producers (first trophic level) and zooplankton are herbivores (second trophic level), but they are written in reverse order, making the second trophic level missing or improperly placed in sequence.
2. Alternatively, considering the options, the food chain 'Zooplankton, Phytoplankton, small fish, large fish' lists zooplankton before phytoplankton, disrupting the producers-first rule of the second trophic level.

**Answer:** (b) Zooplankton, Phytoplankton, small fish, large fish

> Common mistake: Confusing the order of producers and primary consumers in aquatic food chains.

### Question 18

*1 mark · Assertion and reason*

Assertion (A) : Accumulation of harmful chemicals is maximum in the organisms at the highest trophic level of a food chain.
Reason (R) : Harmful chemicals are sprayed on the crops to protect them from diseases and pests.

- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Assertion (A) is false, but Reason (R) is true.

**Solution**

1. Both statements are true and explain biological magnification, but Reason (R) is the source of chemicals, not the correct chemical explanation of why accumulation increases at higher trophic levels.

**Answer:** Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

> Common mistake: Selecting option (a) by assuming the presence of chemicals on crops explains the progressive accumulation process.

### Question 33

*3 marks · Short answer*

(A) $\text{Plants} \rightarrow \text{Deer} \rightarrow \text{Lion}$
In the given food chain, what will be the impact of removing all the organisms of second trophic level on the first and third trophic level ? Will the impact be the same for the organisms of the third trophic level in the above food chain if they were present in a food web ? Justify.

**Solution**

1. In the given food chain, plants form the first trophic level, deer the second trophic level, and lion the third trophic level.
2. If all organisms of the second trophic level (deer) are removed, the population of the first trophic level (plants) will increase due to lack of grazing.
3. The third trophic level (lions) will starve and their population will decrease due to the shortage of food.
4. No, the impact will not be the same if they were present in a food web because lions would have alternative food sources such as other herbivores available in the food web.

**Answer:** Removal of second trophic level increases first trophic level and decreases third in a food chain, but a food web provides alternative food sources.

> Common mistake: Students often confuse the flow of energy and state that the first trophic level will decrease.

### Question 33 (OR)

*3 marks · Short answer*

(B) A gas 'X' which is a deadly poison is found at the higher levels of atmosphere and performs an essential function.
Name the gas and write the function performed by this gas in the atmosphere. Which chemical is linked to the decrease in the level of this gas? What measures have been taken by an international organization to check the depletion of the layer containing this gas?

**Solution**

1. The gas 'X' is ozone ($O_3$), which shields the surface of the earth from harmful ultraviolet (UV) radiations from the Sun.
2. Chlorofluorocarbons (CFCs) are the synthetic chemicals linked to the decrease in the ozone level.
3. The United Nations Environment Programme (UNEP) forged an agreement to freeze CFC production at 1986 levels (Montreal Protocol) worldwide.

**Answer:** Ozone gas protects from UV rays, CFCs cause its depletion, and UNEP's Montreal Protocol regulates CFC production.

> Common mistake: Students write carbon dioxide instead of CFCs as the chemical responsible for ozone depletion.

## CBSE Class 10 Science Question Paper 2023 (Set 31/1/1) with Solutions

### Question 26

*2 marks · Very short answer*

How do harmful chemicals get accumulated progressively at each trophic level in a food chain?

**Solution**

1. Harmful chemicals like pesticides enter the food chain through producers and get absorbed by them.
2. As these chemicals cannot be degraded, their concentration increases progressively at each higher trophic level, a phenomenon known as biological magnification.

**Answer:** Progressive accumulation of non-biodegradable chemicals at each higher trophic level is called biological magnification.

> Common mistake: Failing to mention that the chemicals are non-biodegradable.

### Question 33

*3 marks · Short answer*

(a) (i) Why does a kitchen garden called an artificial ecosystem while a forest is considered to be a natural ecosystem?
(ii) While designing an artificial ecosystem at home, write any two things to be kept in mind to convert it into a self-sustaining system. Give reason to justify your answer.

**Part (a) (i)**

1. A kitchen garden is created, managed, and modified by humans, lacking natural complexity and self-regulation, making it an artificial ecosystem.
2. A forest is a self-sustaining natural unit comprising diverse biotic and abiotic components interacting freely without human intervention, making it a natural ecosystem.

Answer (a) (i): A kitchen garden is man-made and artificially maintained, whereas a forest is self-regulating and natural.

**Part (a) (ii)**

1. Include producers (plants) and primary consumers along with decomposers to ensure nutrient recycling.
2. Provide a continuous energy source like sunlight and regular water supply to maintain biological processes.

Answer (a) (ii): Provisions for a light source and balanced biotic components (producers, consumers, decomposers) must be included to ensure energy flow and nutrient recycling.

**Answer:** Kitchen gardens are created and maintained by humans (artificial), whereas forests exist naturally. To make an artificial system self-sustaining, producers, consumers, and decomposers must be included with adequate light and water.

> Common mistake: Omitting decomposers while listing components of a self-sustaining artificial ecosystem.

### Question 33 (OR)

*3 marks · Short answer*

(b) (i) Construct a food chain of four trophic levels comprising the following : Hawk, snake, plants, rat.
(ii) $20,000\text{ J}$ of energy was transferred by the producers to the organism of second trophic level. Calculate the amount of energy that will be transferred by organisms of the third trophic level to the organisms of the fourth trophic level.

**Part (b) (i)**

1. Identify the four organisms: Plants, rat, snake, hawk.
2. Arrange them in proper trophic sequence: Plants (Producer) $\to$ Rat (Herbivore) $\to$ Snake (Carnivore) $\to$ Hawk (Top Carnivore).

Answer (b) (i): Plants $\to$ Rat $\to$ Snake $\to$ Hawk

**Part (b) (ii)**

1. Energy at the second trophic level (Rat) = $20,000\text{ J}$.
2. According to the 10% law, only 10% of energy is transferred to the next trophic level.
3. Energy at third trophic level (Snake) = $10\% \text{ of } 20,000\text{ J} = 2,000\text{ J}$.
4. Energy at fourth trophic level (Hawk) = $10\% \text{ of } 2,000\text{ J} = 200\text{ J}$.

Answer (b) (ii): $200\text{ J}$

**Answer:** Food chain: Plants $\to$ Rat $\to$ Snake $\to$ Hawk. Energy transferred to fourth trophic level is $2\text{ J}$.

> Common mistake: Calculating 10% from the producer level directly for the fourth trophic level without stepping through the third trophic level, or making calculation errors with zeroes.

## CBSE Class 10 Science Question Paper 2022 (Set 31/1/1) with Solutions

### Question 7

*2 marks · Short answer*

(a) What is ozone ? How is it formed in the upper layers of the Earth's atmosphere ? How does ozone affect our ecosystem ?

**Part (a)**

1. Ozone is a molecule formed by three atoms of oxygen ($O_3$).
2. High energy UV radiations split apart molecular oxygen ($O_2$) into free oxygen ($O$) atoms, which then combine with molecular oxygen to form ozone.
3. Ozone shields the surface of the earth from harmful ultraviolet (UV) radiation from the Sun which can cause skin cancer and damage ecosystems.

Answer (a): Ozone ($O_3$) is formed in the upper atmosphere by the action of UV rays on oxygen molecules and protects the ecosystem by absorbing harmful UV radiation.

**Answer:** Ozone is a molecule formed by three atoms of oxygen ($O_3$), which shields the surface of the earth from harmful UV radiation.

> Common mistake: Confusing oxygen ($O_2$) with ozone ($O_3$) in the formation reaction.

### Question 7 (OR)

*2 marks · Short answer*

(b) (i) List two human-made ecosystems.
(ii) "We do not clean a pond in the same manner as we do in an aquarium." Give reason to justify this statement.

**Part (i)**

1. Two human-made ecosystems are: Crop field and Aquarium.

Answer (i): Crop field and aquarium

**Part (ii)**

1. An aquarium is an artificial and incomplete ecosystem lacking natural self-sustaining food webs and decomposers.
2. A pond is a natural, self-sustaining ecosystem where natural recycling and cleansing mechanisms operate by themselves.

Answer (ii): An aquarium is artificial and lacks the natural self-cleaning mechanisms and decomposers present in a natural pond ecosystem.

**Answer:** Crop fields and aquariums are human-made ecosystems; a pond is a natural self-sustaining ecosystem whereas an aquarium is artificial and lacks natural decomposers and self-regulation.

> Common mistake: Stating that aquariums need cleaning because they are bigger, instead of recognizing them as artificial, closed ecosystems.

### Question 13

*3 marks · Short answer*

(a) Name the group of organisms which form in the first trophic level of all food chains. Why are they called so ?
(b) Why are the human beings most adversely affected by bio-magnification ?
(c) State one ill-effect of the absence of decomposers from a natural ecosystem.

**Part (a)**

1. Producers (or autotrophs / green plants) form the first trophic level of all food chains.
2. They are called so because they can manufacture their own food using solar energy through photosynthesis.

Answer (a): Producers, because they make their own food using sunlight.

**Part (b)**

1. Human beings occupy the topmost position in most food chains.
2. Due to biological magnification, harmful chemicals and pesticides get accumulated in maximum concentration at the highest trophic level.

Answer (b): Because humans occupy the top trophic level where toxic chemicals concentrate the most.

**Part (c)**

1. In the absence of decomposers, the recycling of nutrients in the biosphere would not take place, leading to accumulation of dead organic matter.

Answer (c): Nutrient recycling stops and dead organic matter accumulates.

**Answer:** Producers form the first trophic level, humans suffer maximum bio-magnification due to being at the top of the food chain, and absence of decomposers stops nutrient recycling.

> Common mistake: Confusing producers with consumers in the first trophic level.

## Related pages

- [Our Environment: NCERT solutions](https://www.swavid.com/science/class/10/chapter/our-environment/ncert-solutions)
- [All CBSE Class 10 Science papers](https://www.swavid.com/cbse/class-10/science/previous-year-papers)

Solutions written by SwaVid, a personal AI tutor for Class 6 to 10 Maths and Science. Practise this chapter free: https://www.swavid.com/start/student