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Class 10 Our Environment: cheat sheet
CBSE Science. Ecosystems, food chains and energy flow, biological magnification, the ozone layer, and managing waste.
Key ideas
- An ecosystem is the living things (biotic) and the non-living surroundings (abiotic) of an area, working together.
- Food chains start with producers (green plants), then herbivores, then carnivores; each step is a trophic level.
- Only about 10% of the energy at one trophic level passes on to the next, so food chains are short.
- Decomposers break down dead matter and return nutrients to the soil.
- Harmful chemicals such as pesticides build up at each level of a food chain (biological magnification), so top consumers get the most.
- The ozone layer high in the atmosphere blocks harmful ultraviolet rays; chlorofluorocarbons (CFCs) damage it.
- Biodegradable waste is broken down by microbes; non-biodegradable waste such as plastic is not.
Remember
| The 10% law | plants 10,000 J → herbivores 1,000 J → carnivores 100 J → top carnivores 10 J |
| Food chain | grass → deer → lion |
| Ozone | O₃, formed from O₂ by ultraviolet light |
Watch out
- Saying energy passes on fully from one level to the next (only about 10%).
- Thinking biological magnification is greatest at the producers (it is greatest at the top).
- Calling plastic biodegradable.
Worked example
Sunlight falling on a field gives 1,000,000 J of energy. The leaves capture 1% of it. In the food chain leaves → caterpillar → sparrow → hawk, find the energy at each level using the 10 per cent law. Why can this chain not be very long?
Working: 1,000,000 × 1% = 10,000 J; then divide by 10 at each level
Answer: leaves: 10,000 J; caterpillar: 1,000 J; sparrow: 100 J; hawk: 10 J. Very little energy is left at the top, too little to support another level.
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