Our Environment Class 10 Notes (2026-27) — CBSE
Class 10 Science Chapter 13 notes: ecosystems, food chains and trophic levels, the 10% energy law, biological magnification, the ozone layer and waste management.
Our Environment — Class 10 Science Notes
Chapter Snapshot
This chapter looks at how living things interact with each other and with their surroundings in an ecosystem — the flow of food and energy through food chains, the 10% law, biological magnification, the protective ozone layer, and the management of waste.
Board relevance: a shorter chapter that reliably gives a food-chain/trophic-level question and an ozone or waste-management question. Easy marks if you know the definitions and the 10% law.
Key Concepts & Definitions
Ecosystem — all the interacting organisms in an area together with their non-living environment. It has two components:
- Biotic (living) — plants, animals, microorganisms.
- Abiotic (non-living) — sunlight, temperature, water, soil, air.
Ecosystems can be natural (forest, pond, lake) or artificial/man-made (aquarium, garden, crop field).
Organisms by role:
- Producers (autotrophs) — green plants and algae; make food by photosynthesis.
- Consumers (heterotrophs) — depend on others for food: herbivores (eat plants), carnivores (eat animals), omnivores (both), parasites.
- Decomposers — bacteria and fungi that break down dead organisms, returning nutrients to the soil.
Food Chains, Food Webs and Trophic Levels
Food chain — a series of organisms through which food energy passes, each eating the one before it:
Grass → Grasshopper → Frog → Snake → Eagle
Trophic levels — the steps in a food chain:
- T1: Producers (grass) → T2: Primary consumers (herbivores, grasshopper) → T3: Secondary consumers (frog) → T4: Tertiary consumers (snake) → and so on.
Food web — many interconnected food chains in an ecosystem; most organisms eat, and are eaten by, more than one kind of organism, so food chains cross to form a web. This makes the ecosystem more stable.
Flow of Energy — The 10% Law
- Energy enters the ecosystem from the Sun; producers capture it by photosynthesis.
- Energy flow is unidirectional (one-way: Sun → producers → consumers) and does not cycle back.
- The 10% law: only about 10% of the energy at one trophic level is transferred to the next; the remaining ~90% is lost as heat and used in life processes (respiration, movement).
- Because so little energy is passed on, food chains are usually limited to 3–4 trophic levels.
Biological Magnification
Some harmful chemicals (like pesticides and DDT) are non-biodegradable — they are not broken down and not excreted, so they build up in the bodies of organisms.
Biological magnification (biomagnification) — the increase in the concentration of these harmful chemicals at each successive trophic level. Since humans are often at the top of food chains, the maximum concentration accumulates in humans, causing serious harm.
Ozone Layer and Its Depletion
Ozone (O₃) is a molecule of three oxygen atoms. High in the atmosphere, it forms the ozone layer, which absorbs harmful ultraviolet (UV) radiation from the Sun.
- UV radiation causes skin cancer, cataracts, and harms crops — so the ozone layer is a protective shield.
- Ozone depletion: chemicals called chlorofluorocarbons (CFCs) — once used in refrigerators, air conditioners, and aerosol sprays — destroy ozone, thinning the layer (the "ozone hole" over Antarctica).
- In 1987 the UNEP (Montreal Protocol) reached an agreement to freeze and reduce CFC production worldwide.
(Note: ozone at ground level is a pollutant; only the high-altitude ozone layer is protective.)
Waste and Its Management
Type Broken down by microbes? Examples
Biodegradable Yes Food waste, paper, cotton, cow dung, dead plants/animals
Non-biodegradable No Plastics, glass, metals, DDT, polythene
- Non-biodegradable waste persists for years and causes pollution; it can enter food chains and cause biomagnification.
- Management: reduce, reuse, recycle; segregate waste; compost biodegradable waste; treat sewage before release.
- Disposing of waste responsibly protects the ecosystem and human health.
Why decomposers matter: by breaking down dead plants and animals, decomposers release nutrients back into the soil, water, and air, keeping them available for producers again. Without decomposers, dead matter and nutrients would pile up and the cycling of materials in the ecosystem would stop. This is why biodegradable waste, which decomposers can act on, is far less harmful to the environment than non-biodegradable waste, which they cannot break down.
Key Facts
Quick facts boards ask directly:
Topic Fact to remember
Living components Biotic
Non-living components Abiotic
Make their own food Producers (green plants)
Break down dead matter Decomposers (bacteria, fungi)
Feeding step in a food chain Trophic level
Energy transferred to next level About 10%
Direction of energy flow Unidirectional (one-way)
Typical food-chain length 3–4 trophic levels
Toxins increase up the chain Biological magnification
Highest toxin concentration Top consumers / humans
Ozone formula O₃
Radiation ozone blocks Ultraviolet (UV)
Chemicals that deplete ozone CFCs
Agreement to cut CFCs Montreal Protocol (1987)
Two definitions to quote: Ecosystem — a self-contained unit of living organisms interacting with each other and their non-living environment. Biological magnification — the progressive accumulation of non-biodegradable substances at successive trophic levels of a food chain.
Important Question Patterns
1. Food chain/trophic levels (2–3 marks): construct a food chain; identify producers/consumers/decomposers; assign trophic levels.
2. 10% law (2–3 marks): state the law; calculate energy available at a higher level; why chains are short.
3. Biological magnification (2–3 marks): define it; why the concentration is highest in top consumers/humans.
4. Ozone (2–3 marks): role of the ozone layer; how CFCs deplete it; effects of UV; the Montreal Protocol.
5. Waste management (2 marks): classify wastes as biodegradable/non-biodegradable; effects of non-biodegradable waste; methods of disposal.
⚡ Quick Revision
- Ecosystem = biotic + abiotic components; natural (forest, pond) or artificial (aquarium).
- Producers (plants) → consumers (herbivore/carnivore/omnivore) → decomposers (bacteria, fungi return nutrients).
- Food chain = energy path; trophic levels T1 producers, T2 primary consumers…; food web = interlinked chains.
- Energy flow is one-way (from Sun); 10% law — only 10% passes to the next level → chains limited to 3–4 levels.
- Biological magnification: non-biodegradable toxins (DDT, pesticides) increase up the chain; highest in humans.
- Ozone (O₃) layer absorbs UV; depleted by CFCs → ozone hole; Montreal Protocol reduces CFCs.
- Biodegradable (food, paper — decompose) vs non-biodegradable (plastic, glass, metals — persist). Reduce, reuse, recycle.
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