Levels of organisation

An ecosystem is the interaction between a community of living organisms and their environment. A community is two or more populations of organisms. An ecosystem is the interaction of two or more populations of organisms in their environment.

Producers and consumers

Feeding relationships show what organisms eat or are eaten by others and through this the levels of organisation in an ecosystem. These can be shown in food chains, which add together to make food webs for a habitat.

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 produces biomass. It is this which feeds the rest of the food chain.

All animals above the producer are called consumers. The first is the primary consumer, the next is the secondary consumer. Animals that hunt and kill others are called predators, and those that are hunted and killed are called prey. The top animal in the feeding relationship is called the apex predator.


Decomposers are bacteria and fungi, which break down dead organisms in a process called decomposition or rotting. They do this by releasing 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.