CBSE Class 10 Our Environment - MCQ Questions

CBSE Class 10 Biology: Our Environment - Part 1: MCQ Questions

Top 25 MCQs with Answers | Latest CBSE Pattern

1. MCQ 2. VSA 3. SA 4. LA 5. Assertion-Reason 6. Case Study 7. Concepts 8. One-Shot Revision

Welcome to Part 1 of our new 8-part series on the chapter Our Environment. This post contains the top 25 Multiple Choice Questions (MCQs) to help you score full marks in your board exams. Let's begin!

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Top 25 MCQs - Our Environment

Question 1: Food Chain

CBSE PYQ 2023

Which of the following constitutes a food chain?

(a) Grass, wheat and mango (b) Grass, goat and human (c) Goat, cow and elephant (d) Grass, fish and goat

(b) Grass, goat and human

Explanation: A food chain shows the flow of energy. Grass (producer) is eaten by a goat (primary consumer), which is then eaten by a human (secondary consumer).

Question 2: 10% Energy Law

CBSE PYQ 2020

In an ecosystem, the 10% of energy available for transfer from one trophic level to the next is in the form of:

(a) Heat energy (b) Chemical energy (c) Light energy (d) Mechanical energy

(b) Chemical energy

Explanation: Energy is stored as chemical energy in the bonds of organic molecules (food) and is transferred when one organism eats another.

Question 3: Biomagnification

CBSE PYQ 2022

Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as:

(a) Eutrophication (b) Pollution (c) Biomagnification (d) Accumulation

(c) Biomagnification

Explanation: Biomagnification (or biological magnification) is the process where certain substances like pesticides become more concentrated in organisms at successively higher levels in a food chain.

Question 4: Friendly Practices

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 parents to drop you (d) All of the above

(d) All of the above

Explanation: All three practices help in conserving resources (reducing plastic use, saving electricity, saving fuel) and are therefore environment-friendly.

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Question 5: Ozone Depletion Cause

CBSE PYQ 2024

The depletion of the ozone layer in the upper atmosphere is mainly caused by:

(a) Carbon dioxide (b) Chlorofluorocarbons (CFCs) (c) Methane (d) Sulphur dioxide

(b) Chlorofluorocarbons (CFCs)

Explanation: CFCs, once used in refrigerators and aerosol sprays, rise to the stratosphere and release chlorine atoms, which catalytically destroy ozone molecules.

Question 6: 10% Law Calculation

CBSE PYQ 2025

In a food chain, if 10,000 J of energy is available to the producer (plants), how much energy will be available to the secondary consumer?

(a) 1000 J (b) 100 J (c) 10 J (d) 1 J

(b) 100 J

Explanation: According to the 10% law:
Producer (Plant): 10,000 J
Primary Consumer (Herbivore): 10% of 10,000 J = 1000 J
Secondary Consumer (Carnivore): 10% of 1000 J = 100 J

Question 7: Ecosystem Definition

An ecosystem includes:

(a) Only living organisms (b) Only non-living components (c) Both living organisms and non-living components (d) Only producers and consumers

(c) Both living organisms and non-living components

Explanation: An ecosystem is a community of biotic (living) components interacting with their abiotic (non-living) environment.

Question 8: Non-Biodegradable

CBSE PYQ 2022

Which of the following is a non-biodegradable substance?

(a) Paper (b) Cotton cloth (c) Plastic (d) Vegetable peels

(c) Plastic

Explanation: Non-biodegradable substances, like plastic, cannot be broken down by microorganisms into harmless natural substances.

Question 9: Ozone Function

CBSE PYQ 2023

What is the main function of ozone in the upper atmosphere?

(a) It traps heat and keeps the Earth warm. (b) It absorbs harmful ultraviolet (UV) radiation from the Sun. (c) It is essential for the respiration of organisms. (d) It prevents acid rain.

(b) It absorbs harmful ultraviolet (UV) radiation from the Sun.

Explanation: The ozone layer (O₃) acts as a protective shield, absorbing most of the Sun's harmful UV-B radiation, which can cause skin cancer and harm plants.

Question 10: Producers

Organisms that manufacture their own food from simple inorganic substances are called:

(a) Consumers (b) Producers (c) Decomposers (d) Carnivores

(b) Producers

Explanation: Producers (like plants and algae) use photosynthesis to convert light energy and inorganic substances (CO₂, water) into organic food (glucose).

Question 11: The "3 Rs"

What are the "3 Rs" to save the environment?

(a) Reduce, Reuse, Recycle (b) Read, Rewrite, Remember (c) Reduce, Replant, Regenerate (d) Reuse, Rebuild, Restore

(a) Reduce, Reuse, Recycle

Explanation: These three are the fundamental principles of waste management to minimize environmental impact.

Question 12: Decomposers

CBSE PYQ 2020

Organisms which break down dead organic matter and waste products are called:

(a) Producers (b) Carnivores (c) Herbivores (d) Decomposers

(d) Decomposers

Explanation: Decomposers, such as bacteria and fungi, play a crucial role in recycling nutrients in an ecosystem by breaking down complex organic substances into simple inorganic ones.

Question 13: Food Chain Example

CBSE PYQ 2023

An aquatic food chain is: Grass -> Insect -> Frog -> ? -> Hawk. What organism fits in the blank?

(a) Snake (b) Deer (c) Rabbit (d) Goat

(a) Snake

Explanation: In this food chain, the frog (tertiary consumer) would be eaten by a snake (quaternary consumer), which is then eaten by the hawk (top consumer).

Question 14: Ecosystem Unit

The functional unit of the environment, consisting of biotic and abiotic components, is called:

(a) Food web (b) Ecosystem (c) Trophic level (d) Food chain

(b) Ecosystem

Explanation: This is the definition of an ecosystem.

Question 15: Abiotic Component

Which of the following is an abiotic component of an ecosystem?

(a) Bacteria (b) Plants (c) Fungi (d) Sunlight

(d) Sunlight

Explanation: Abiotic components are the non-living parts of an ecosystem. Sunlight, water, air, and soil are abiotic. Bacteria, plants, and fungi are biotic (living).

Question 16: Trophic Levels

CBSE PYQ 2024

In the given food chain: Plants -> Deer -> Lion, what trophic level do the Lions represent?

(a) First Trophic Level (T1) (b) Second Trophic Level (T2) (c) Third Trophic Level (T3) (d) Fourth Trophic Level (T4)

(c) Third Trophic Level (T3)

Explanation:
T1: Producers (Plants)
T2: Primary Consumers (Deer)
T3: Secondary Consumers (Lion)

Question 17: Food Web

The interconnected network of food chains in an ecosystem is called a:

(a) Food web (b) Trophic level (c) Ecological pyramid (d) Energy flow

(a) Food web

Explanation: A food web is more realistic than a food chain as it shows multiple feeding relationships and how different food chains are interlinked.

Question 18: Waste Disposal

Which of the following would be the most effective way to dispose of biodegradable waste?

(a) Incineration (b) Composting (c) Landfill (d) Recycling

(b) Composting

Explanation: Composting uses decomposers (bacteria, fungi) to naturally break down biodegradable waste into nutrient-rich humus, which is beneficial for soil.

Question 19: Energy Source

The primary source of energy in almost all ecosystems is:

(a) Geothermal energy (b) Solar energy (c) Chemical energy from food (d) Wind energy

(b) Solar energy

Explanation: Producers at the base of the food chain capture solar energy through photosynthesis, which then flows through the entire ecosystem.

Question 20: Montreal Protocol

CBSE PYQ 2025

Which international agreement was signed to limit the production of ozone-depleting substances?

(a) Kyoto Protocol (b) Paris Agreement (c) Montreal Protocol (d) Stockholm Convention

(c) Montreal Protocol

Explanation: The Montreal Protocol (1987) is an international treaty designed to protect the ozone layer by phasing out the production of substances like CFCs.

Question 21: Artificial Ecosystem

Which of the following is an example of an artificial ecosystem?

(a) Forest (b) Lake (c) Aquarium (d) Desert

(c) Aquarium

Explanation: An aquarium is a man-made and maintained ecosystem. Forests, lakes, and deserts are natural ecosystems.

Question 22: Energy Flow

CBSE PYQ 2024

The flow of energy in an ecosystem is always:

(a) Unidirectional (b) Bidirectional (c) Multidirectional (d) Cyclic

(a) Unidirectional

Explanation: Energy flows in one direction: from the Sun -> to Producers -> to Consumers. It does not flow backward (e.g., from a goat back to the grass). Nutrients, however, are cyclic.

Question 23: First Trophic Level

Which organisms are at the first trophic level (T1)?

(a) Herbivores (b) Carnivores (c) Decomposers (d) Producers

(d) Producers

Explanation: The first trophic level is always occupied by producers (plants, algae) that produce their own food.

Question 24: Paper vs. Plastic

CBSE PYQ 2023

The use of disposable paper cups is considered better than disposable plastic cups because:

(a) Paper cups are cheaper. (b) Paper cups are biodegradable. (c) Paper cups are more stylish. (d) Paper cups are lighter.

(b) Paper cups are biodegradable.

Explanation: Paper is a biodegradable material, meaning it can be broken down by microorganisms and will not persist in the environment for centuries like plastic.

Question 25: Trophic Level Limits

Which of the following limits the number of trophic levels in a food chain?

(a) Decrease in energy at higher trophic levels (b) Insufficient food supply (c) Pollution (d) Limited space

(a) Decrease in energy at higher trophic levels

Explanation: Due to the 10% law, only a small fraction of energy is transferred to the next level. After 3 or 4 levels, the available energy is too low to support another population.