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I. Chapter Summary
The chapter “Our Environment” focuses on how human activities impact the environment. It explains ecosystems, their components, the concept of trophic levels, food chains, food webs, and energy flow in ecosystems. It highlights the problem of biodegradable vs. non-biodegradable waste, and the harmful effects of ozone depletion and pollution from man-made substances. The chapter encourages sustainable living and environmental awareness.
II. Key Concepts Covered
Concept
Description
Ecosystem
A system formed by the interaction of all living (biotic) and non-living (abiotic) components in an environment.
Components of Ecosystem
– Biotic: Plants, animals, microorganisms
– Abiotic: Air, water, temperature, sunlight
Food Chain
Linear sequence of organisms through which energy is transferred. (Producer → Primary consumer → Secondary consumer, etc.)
Food Web
A network of interconnected food chains showing how organisms are related through multiple feeding relationships.
Trophic Levels
Levels in a food chain based on energy transfer (Producer → Primary → Secondary → Tertiary).
Energy Flow
Energy flows in one direction and decreases at each trophic level (only ~10% energy is passed on).
Biodegradable Waste
Can be decomposed by natural processes (e.g., food waste, paper).
Non-Biodegradable Waste
Cannot be easily broken down (e.g., plastics, pesticides).
Ozone Layer
Protects life by blocking UV rays; getting depleted by CFCs.
III. Important Questions
(A) Multiple Choice Questions (1 Mark)
Which of the following is a non-biodegradable substance? a) Paper b) Cotton c) Plastic ✅ (PYQ 2020) d) Fruits
Which trophic level receives the maximum energy? a) Producers ✅ b) Primary consumers c) Secondary consumers d) Tertiary consumers
What percentage of energy is transferred from one trophic level to the next? a) 100% b) 50% c) 10% ✅ (PYQ 2021) d) 90%
Ozone layer is mainly found in: a) Troposphere b) Stratosphere ✅ c) Mesosphere d) Thermosphere
(B) Short Answer Questions (2/3 Marks)
What is an ecosystem? Name its components.
Why is the energy flow in a food chain unidirectional?(PYQ 2019)
State two differences between biodegradable and non-biodegradable substances.
What are trophic levels? Why do they not exceed four or five?
(C) Long Answer Questions (5 Marks)
Explain the flow of energy in an ecosystem. Draw a diagram of a food chain and show energy transfer.
What is the role of decomposers in the ecosystem? Why are they important?
Describe the harmful effects of using non-biodegradable substances and suggest methods for disposal.
What are the causes and effects of ozone layer depletion? What steps can be taken to protect it?
(D) HOTS (Higher Order Thinking Skills)
Why is it more sustainable to be a vegetarian from an energy point of view?
If all decomposers were removed from the ecosystem, what would be the consequences?
IV. Key Formulas/Concepts
Concept
Description
10% Law
Only 10% of energy is transferred to the next trophic level; the rest is lost as heat.
Trophic Level Examples
– Producer: Grass
– Primary Consumer: Grasshopper
– Secondary Consumer: Frog
– Tertiary Consumer: Snake
Biodegradable Examples
Leaves, vegetable peels, wood
Non-Biodegradable Examples
Plastics, glass, DDT, polythene
Ozone Depletion Cause
Release of CFCs (chlorofluorocarbons) from aerosols and refrigerants
V. Deleted Portions (CBSE 2025–2026)
No portions have been deleted from this chapter as per the rationalized NCERT textbooks.
VI. Chapter-Wise Marks Bifurcation (Estimated – CBSE 2025–2026)
Unit/Chapter
Estimated Marks
Type of Questions Typically Asked
Chapter 13: Our Environment
4–6 Marks
1 Long Answer, 1–2 Short Answers, 1–2 MCQs
VII. Previous Year Questions (PYQs)
Year
Marks
Question
2021
1
What percentage of energy is transferred to the next trophic level? (10%)
2020
1
Which of the following is a non-biodegradable substance? (Plastic)
2019
3
Why is energy flow unidirectional in food chains?
2018
5
Explain energy transfer in a food chain with a diagram.
VIII. Real-World Application Examples to Connect with Topics
Concept
Real-Life Application
Trophic Levels
Wildlife conservation and food web balance
Waste Management
Segregation of biodegradable and non-biodegradable waste at home
Ozone Layer Protection
Use of CFC-free refrigerators, banning harmful aerosols
Sustainable Living
Composting, using paper bags instead of plastic
IX. Student Tips & Strategies for Success
Time Management
Revise definitions and examples daily in short bursts.
Practice diagram-based questions (food chain, trophic levels).
Exam Preparation
Memorize 10% law and its application in food chains.
Understand and differentiate clearly between waste types and ecosystem components.
Stress Management
Use color-coded diagrams to simplify concepts.
Study in groups to discuss practical examples from everyday life.
X. Career Guidance & Exploration (Class-Specific)
For Classes 9–10
Streams
Science: Environmental Science, Ecology, Biology
Commerce: Environmental Economics, Waste Management Business
