Levels of organisation

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

Radiation from the sun is the source of energy for living organisms.

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, which 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 and 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.

OrganismHow it gets energy
Primary consumerEat the producers, most are herbivores
HerbivoresEat only plants
Secondary consumerEating primary consumers, most are carnivores
CarnivoresEat only other animals
Tertiary consumerEating secondary consumers
OmnivoreConsumers which eat both animals and plants so can occupy more than one trophic level in a food chain
DecomposerFeeding on dead and decaying organisms and on the undigested parts of plant and animal matter in faeces