A food chain shows how the organisms in a particular habitat depend on each other as a source of food. At the start of any food chain is a producer which is normally a green plant. It is called a producer because it produces its own energy and food from raw materials it finds in its surroundings. Following on from the producer are the consumers, so called because they must eat something else. The first of these are called primary consumers and they are herbivores as all they eat are plants. Animals that feed on the primary consumers are called secondary consumers whilst tertiary consumers... Show more

A food chain shows how the organisms in a particular habitat depend on each other as a source of food. At the start of any food chain is a producer which is normally a green plant. It is called a producer because it produces its own energy and food from raw materials it finds in its surroundings.

Following on from the producer are the consumers, so called because they must eat something else. The first of these are called primary consumers and they are herbivores as all they eat are plants. Animals that feed on the primary consumers are called secondary consumers whilst tertiary consumers feed on the secondary consumers. Secondary consumers are carnivores or omnivores, as are the tertiary consumers. At the opposite end of a food chain to the producers is the top predator.

Food chains are usually short, rarely containing more than 3 or 4 consumers. This is because there is a loss of both energy and biomass in each stage of the chain. The entire amount of energy and biomass for a food chain is contained in the producers - call that 100%. When this is eaten by the consumers, all of it is passed on. The primary consumer uses some of this energy for respiration in its cells which enables it to stay alive, move etc. The rest becomes part of the biomass of the primary consumer and is passed along the food chain; so less than the original 100% is available to the secondary consumers. This happens at each stage of the food chain and nothing hunts the top predator because it would take more energy than would be gained from eating it.

We can see the loss of biomass and energy by observing the numbers and sizes of organisms in food chains. The biomass of living organisms at each successive stage in a food chain can be represented using pyramids of numbers and/or pyramids of biomass.

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