Our Environment Class 10 Notes | CBSE Science Chapter 15 Simplified & Explained (2025–26)

 Our Environment Class 10 Notes

Boost your Class 10 Science exam prep with our simplified notes on Chapter 15 – Our Environment (NCERT). Specially designed for CBSE 2025–26 students, these notes break down key concepts like ecosystems, food chains, and waste management in a clear, easy-to-understand way.

Study on the go with our free downloadable PDF, perfect for quick revision and stress-free learning. Whether you're revising or learning this chapter for the first time, this resource will help you grasp the essentials with confidence.

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Subject	Science
Class	10
Board	CBSE & State Boards
Chapter No.	13
Chapter Name	Our Environment
Type	Notes
Session	2025-26

Table of Contents

• EcoSystem - What are its Components?
  • Types of Ecosystems:
  • Preparation of a self-sustainable artificial aquatic ecosystem
  • Role of decomposers in an ecosystem
  • Food Chains and Webs
• How do our Activities Affect the Environment?
  • Ozone Layer and How it is Getting Depleted
  • Managing the Garbage we Produce

EcoSystem - What are its Components?

Ecosystem: All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.

An ecosystem consists of

• biotic components comprising living organisms
• abiotic components comprising physical factors like temperature, rainfall, wind, soil, and animals.

Types of Ecosystems:

1. Natural ecosystem: Forests, ponds, and lakes.
2. Human-made (artificial) ecosystem: Gardens, aquariums, and crop fields.

Preparation of a self-sustainable artificial aquatic ecosystem

1. Take a large jar filled with water.
2. Provide oxygen through an oxygen pump (aerator) and fish food that is available in the market.
3. Add aquatic plants and animals.
4. Aquatic plants/Producers provide O2 during photosynthesis.
5. Aquatic animals/Consumers release CO2 for the process of photosynthesis.
6. Decomposers are also important for the natural cleaning of the aquarium.

Role of decomposers in an ecosystem

1. They clean the environment.
2. They decompose biodegradable substances into useful substances.
3. They release nutrients into the soil by decomposing dead and decaying matter, thus making the soil fertile.
4. They maintain the nutrient pool by returning the nutrients in the pool.

Food Chains and Webs

Plant → Grasshopper → Frog → Snake

Each step or level of the food chain forms a trophic level.

• The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or consumers.
• The herbivores or the primary consumers come at second,
• small carnivores or the secondary consumers at the third
• larger carnivores or tertiary consumers form the fourth trophic level.

The flow of energy between trophic levels:

1. The flow of energy is unidirectional.
2. Terrestrial plants take about 1% of the Sun’s energy and change it to chemical energy.
3. A great deal of energy is lost as heat/is used for digestion/ doing work/ growth and reproduction.
4. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers.
5. Food chains are mainly of 3-4 trophic levels (because of the 10% law).
6. The number of producers is maximum and the number reduces in subsequent trophic levels.
7. Food webs are more common as compared to isolated food chains.
8. Biological magnification can be observed.

10 percent law: Only 10% of energy is transferred to the next trophic level. The remaining 90% of energy is used in life processes (digestion, growth, reproduction, etc.) by the present trophic level.

Food Chain	Food Web
i. Food chain is a series of organisms feeding on one another.	i. Food web consists of a number of interlinked food chains.
ii. Members of higher trophic level feed upon a single type of organism of the lower trophic level.	ii. Members of higher trophic levels can feed upon organisms of the lower trophic levels of other food chains.
iii. It does not have any effect on improving the adaptability and competitiveness of the organism.	iii. It improves the adaptability and competitiveness of the organism.
iv. Example: Grass → Grasshopper → Frog → Snake → Hawk.	iv. Example: A hawk might also eat a mouse, a frog, or some other animal. The snake may eat a beetle, a caterpillar, or some other animal.

Biological Magnification: Non-biodegradable pesticides accumulate progressively at each trophic level. This phenomenon is known as biological magnification.

The consequences of human beings occupying the top level in any food chain are:

1. A maximum level of bio-magnification occurs here because of progressive accumulation.
2. We get a very small amount of energy as only 10% of the previous energy gets transferred at each trophic level.

How do our Activities Affect the Environment?

Ozone Layer and How it is Getting Depleted

• Ozone (O3) is a molecule formed by three atoms of oxygen.
• Ozone is a deadly poison.
• It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.

Formation of ozone:

The high-energy UV radiations break down the O2 molecules into free oxygen (O) atoms.

These oxygen atoms then combine with oxygen (O2) molecules to form the ozone molecule.

Cause of Ozone depletion: Synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers lead to the depletion of the ozone layer.

Steps taken to limit the damage:

• Depletion of the ozone layer can be prevented by not using synthetic chemicals like CFCs, that deplete the O3 layer.
• Many developing and developed countries have signed and are obeying the directions of UNEP (United Nations Environment Programme) to freeze or limit the production and usage of CFCs at 1986 levels.

Managing the Garbage we Produce

Biodegradable Substances	Non-biodegradable Substances
i. Substances that are broken down by biological processes are called biodegradable substances.	i. Substances that are not broken down by biological processes are called non-biodegradable substances.
ii. Examples – Wood, paper, etc.	ii. Examples – Plastic, DDT, etc.

Excess generation of biodegradable wastes can be harmful as:

1. Its decomposition is a slow process leading to the production of foul smells and gases.
2. It can be the breeding ground for germs that create unhygienic conditions.

The problems caused by non-biodegradable wastes are:

1. They cause biomagnification.
2. They increase pollution.
3. They make the environment unclean.
4. They kill useful microorganisms.

Eco-friendly activities are:

1. Walk or cycle for short distances to reduce the use of vehicles running on fossil fuels.
2. Use both sides of the paper to reduce its use. Fewer trees will be cut to make more paper.
3. Separation of biodegradable and non-biodegradable wastes.
4. Gardening
5. Use of gunny bags/paper bags in place of polythene/plastic bags.
6. Use of compost and vermicompost in place of fertilizers.
7. Harvesting rainwater, etc.

The reasons for the shift from plastic to kulhads and then finally to paper cups are:

• The use of plastic cups raised the concern about hygiene thus they were replaced by disposable plastic cups.
• Disposable plastic cups are non-biodegradable and harm the environment. They were thus replaced by kulhads.
• Kulhads made of clay on a large scale resulted in the loss of top fertile soil.
• Now, disposable paper cups are used because – the paper can be recycled, is biodegradable, and is an eco-friendly material that does not cause environmental pollution.

📘 Chapter 15: Our Environment – NCERT Solutions

Subject: Class 10 Science (Biology)
Board: CBSE
Book: NCERT
Chapter No.: 15
Chapter Title: Our Environment

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🔹 Intext Questions – Page 257

Q1. What are the trophic levels? Give an example of a food chain and state the different trophic levels in it.
✅ Answer:
Trophic levels are the steps in a food chain where organisms obtain energy.
Example:
Grass → Grasshopper → Frog → Snake → Hawk

• Grass – Producer (1st trophic level)

• Grasshopper – Primary consumer (2nd)

• Frog – Secondary consumer (3rd)

• Snake – Tertiary consumer (4th)

• Hawk – Quaternary consumer (5th)

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Q2. What is the role of decomposers in the ecosystem?
✅ Answer:
Decomposers like bacteria and fungi break down dead organisms and recycle nutrients back into the environment, maintaining ecological balance.

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🔹 Intext Questions – Page 258

Q1. Why are some substances biodegradable and some non-biodegradable?
✅ Answer:
Biodegradable substances can be broken down by microorganisms (like food waste), while non-biodegradable ones (like plastic) cannot be easily decomposed and persist in the environment.

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Q2. Give any two ways in which non-biodegradable substances would affect the environment.
✅ Answer:

1. Cause pollution and health hazards

2. Harm animals and aquatic life when consumed mistakenly

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Q3. What is ozone and how does it affect any ecosystem?
✅ Answer:
Ozone (O₃) is a gas found in the stratosphere. It absorbs harmful UV rays from the Sun, protecting life on Earth. Depletion leads to increased UV exposure, harming living organisms.

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Q4. How can you help in reducing the problem of waste disposal? Give any two methods.
✅ Answer:

1. Segregate waste into biodegradable and non-biodegradable

2. Reuse and recycle materials whenever possible

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🔹 Back Exercise Questions (Pages 260–261)

Q1. Which of the following groups contain only biodegradable items?
(a) Grass, flowers, leather
(b) Grass, wood, plastic
(c) Fruit peels, cake, lime juice
(d) Cake, wood, grass

✅ Answer:
(c) Fruit peels, cake, lime juice

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Q2. Which of the following constitute a food chain?
(a) Grass, wheat, mango
(b) Grass, goat, human
(c) Goat, cow, elephant
(d) Grass, fish, goat

✅ Answer:
(b) Grass, goat, human

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Q3. Which of the following are environmental-friendly practices?
(a) Carrying cloth bags
(b) Switching off lights when not in use
(c) Walking or cycling for short distances
(d) All of the above

✅ Answer:
(d) All of the above

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Q4. What will happen if we kill all the organisms in one trophic level?
✅ Answer:
It will disturb the food chain and ecosystem. The organisms in the next trophic level will lack food and decrease, while the previous level may overpopulate.

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Q5. Will the impact of removing all organisms in one trophic level be different for different trophic levels?
✅ Answer:
Yes. Removing producers collapses the entire chain. Removing top-level consumers might increase population at lower levels, causing imbalance.

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Q6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
✅ Answer:
It’s the increase in concentration of harmful substances (like pesticides) at higher trophic levels. Yes, top-level consumers have the highest concentration.

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Q7. What are the problems caused by the non-biodegradable wastes that we generate?
✅ Answer:

• Soil and water pollution

• Harm to wildlife

• Health issues in humans

• Clogging of drains

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Q8. If all the waste we generate is biodegradable, will this have no impact on the environment?
✅ Answer:
Even biodegradable waste can cause pollution if not managed properly. It can lead to foul smell, breeding of flies, and depletion of oxygen in water bodies.

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Q9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
✅ Answer:
Ozone protects Earth from harmful UV rays. Its depletion leads to health risks and ecological damage.
Steps taken:

• Banning of CFCs

• Montreal Protocol

• Promoting eco-friendly refrigerants

📘 Chapter 15: Our Environment – CBSE Past Exam Questions

Subject: Science – Biology
Grade: Class 10
Chapter: 15
Type: Theory (Mostly 1M, 2M, and 3M questions)

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🔹 1-MARK QUESTIONS

1. What are biodegradable substances? Give one example.
   📅 CBSE 2020
   ✅ Answer: Substances decomposed by microorganisms. Example: Vegetable peels.

2. Why is ozone layer important for the existence of life on Earth?
   📅 CBSE 2016, 2022
   ✅ Answer: It blocks harmful UV radiation from the Sun.

3. Mention one cause of ozone layer depletion.
   📅 CBSE 2017
   ✅ Answer: Use of chlorofluorocarbons (CFCs).

4. Give an example of a non-biodegradable pollutant.
   📅 CBSE 2018
   ✅ Answer: Plastic

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🔹 2-MARK QUESTIONS

1. What is biological magnification? Explain with the help of a food chain.
   📅 CBSE 2019, 2023
   ✅ Answer: Increase in concentration of harmful chemicals like DDT in higher trophic levels.

2. Write two differences between biodegradable and non-biodegradable substances.
   📅 CBSE 2017
   ✅ Answer:

• Biodegradable: decomposed by microbes; Non-biodegradable: not easily decomposed

• Examples: paper vs. plastic

3. Why is improper disposal of waste a curse to the environment?
   📅 CBSE 2016
   ✅ Answer: It pollutes soil, water, air and harms biodiversity.

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🔹 3-MARK QUESTIONS

1. Explain the flow of energy in a food chain. Why is it unidirectional?
   📅 CBSE 2018, 2020
   ✅ Answer: Energy passes from one trophic level to the next but is lost as heat, so it doesn’t return to the previous level.

2. What are trophic levels? Give an example. What is the percentage of energy transfer between levels?
   📅 CBSE 2022
   ✅ Answer: Each step in food chain is a trophic level. Only 10% energy is passed to the next level.

3. Give reasons for the following:
   (a) Ozone layer depletion is a threat to life.
   (b) It is better to use jute bags than plastic bags.
   📅 CBSE 2017, 2021
   ✅ Answer:
   (a) More UV rays cause cancer and crop failure
   (b) Jute is biodegradable; plastic causes pollution

4. Explain with an example how energy flows through an ecosystem.
   📅 CBSE 2019
   ✅ Answer: Producers → herbivores → carnivores. 10% law applies.

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🔹 5-MARK QUESTIONS (Rare but sometimes clubbed in SA II)

1. Describe the importance of decomposers in the ecosystem. 
   📅 CBSE Sample Paper 2020
   ✅ Answer:

• They recycle nutrients

• Prevent accumulation of dead matter

• Without them, ecosystem balance will be disturbed

🧪 High-Yield Topics Frequently Asked

Topic	Expected Marks	Importance
Food chain and trophic levels	1M / 3M	High
10% law and energy flow	2M / 3M	High
Ozone layer & its depletion	1M / 2M	High
Biological magnification	2M / 3M	High
Decomposers and waste management	2M / 3M	Medium
Biodegradable vs. Non-biodegradable	1M / 2M	Medium