Class 10 Science Notes — Chapter 13: Our Environment
Ecosystems, energy flow, waste management, and ozone depletion.
Detailed NCERT notes
- Environment = biotic (living) + abiotic (non-living) surroundings.
- Ecosystem = a self-contained unit where organisms interact with each other and with abiotic components. Types: natural (forest, pond) and artificial (aquarium, crop field).
- Components: producers (autotrophs — plants), consumers (herbivores, carnivores, omnivores), decomposers (bacteria, fungi).
- Food chain: linear sequence — producer → primary consumer → secondary → tertiary. Each stage = trophic level.
- Food web = interconnected food chains; more realistic.
- 10% law of energy transfer (Lindeman): only ~10% of energy at one trophic level is passed to the next; the rest is lost as heat, in life processes.
- Because of the 10% law, food chains are usually limited to 3–4 trophic levels.
- Biomagnification: harmful chemicals (e.g., DDT, mercury) increase in concentration as they move up trophic levels — top predators are worst affected.
- Biodegradable substances: broken down by decomposers (vegetable peel, cotton, paper).
- Non-biodegradable: not decomposed (plastic, glass, DDT); accumulate as pollution.
- Impact: sewage in water bodies causes eutrophication and BOD rise; solid waste causes land pollution.
- Ozone layer (in stratosphere): protects Earth from harmful UV radiation.
- Ozone depletion: caused by CFCs (from refrigerators, aerosols). CFCs release Cl atoms that destroy ozone.
- Consequences: increased UV-B → skin cancer, cataracts, weakened immunity, damage to crops and marine life.
- Montreal Protocol (1987): international agreement to phase out ozone-depleting substances.
- Note: 'Sustainable management of resources' has largely been rationalised out of the chapter — focus on ecosystem + ozone content.
Formulas & key results
- 10% law: energy transferred between trophic levels
- Biomagnification: concentration ↑ up the chain
Mind map
- Ecosystem components → food chain/web → energy flow
- Biodegradable vs non-biodegradable
- Ozone depletion (CFC → UV harm) → Montreal Protocol
Tricks & shortcuts
- Only 10% up — so food chains rarely exceed 4 levels.
- Biomagnification hits top of chain hardest (birds of prey, humans).
Common mistakes to avoid
- Thinking energy is cyclic (it flows one way; matter is cyclic).
- Confusing biodegradable with recyclable.
Competency-based questions & answers
- Q. Why are food chains usually limited to 3–4 trophic levels?A. Only 10% of energy passes to the next level; beyond 4 levels, insufficient energy remains to support another.
- Q. How do plastics harm the environment?A. Non-biodegradable → accumulate as waste; when burnt release toxic gases; block drains; enter food chain as microplastics.
- Q. Explain how CFCs deplete ozone.A. UV breaks CFCs, releasing Cl atoms; each Cl catalytically destroys many ozone molecules — thinning the ozone layer.