Levels of organisation

An ecosystem is the living organisms in a particular area together with the non-living components of the environment, such as soil, air and water.

A habitat is a place where organisms live in an ecosystem. A community is the populations of organisms that live in an ecosystem.

There is a close interaction between the organisms and the non-living components of an ecosystem.

Producers and consumers

Food chains show what organisms eat, or what organisms are eaten by others - in other words, the feeding relationships of organisms - in an ecosystem.

A simple example of a food chain is:

grass → rabbits → foxes

At the base of almost every food chain is a producer. These are plants or algae, which photosynthesise. This means they convert energy from the Sun into glucose during photosynthesis producing biomass. It is this which feeds, and provides energy to the rest of the food chain.

All animals that follow the producer in the food chain are called consumers. The first is the primary consumer, which has fed on the producer. The next is the secondary consumer, which has eaten animals that fed on the producer. Secondary consumers may be eaten by tertiary consumers.

Animals that hunt and kill others are called predators, and those that are hunted and killed are called prey.

In reality, many animals eat more than one type of organism, and food chains combine to make food webs.


Decomposers are organisms that breakdown dead organisms in a process called decomposition or rotting. They include bacteria and fungi. Decomposers release enzymes onto the dead matter and afterwards, consume the broken down substances. They form a vital role in the recycling of matter. When organisms die and decompose, plants absorb the broken down nutrients through their roots.