Our Environment

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.