Food chains

A food chain shows the flow of energy and materials from one organism to the next in a habitat. It begins with a producer.

Producers are green plants which photosynthesise. They use light energy from the sun to convert carbon dioxide from the air and water from the soil into glucose and oxygen. The glucose made can be eaten by other organisms so that they can use it for respiration which releases the energy stored in the glucose. This energy can then be used for their life processes.

In this example of a food chain, grass seeds are eaten by voles, and voles are eaten by barn owls.

A 'grass seeds-vole-barn owl' food chain

The arrows between each organism in the chain always point in the direction of energy flow from the food to the feeder.

The position occupied by an organism in a food chain is known as its trophic level. In the example above:

  1. the producer (grass seed) occupies the first trophic level
  2. the primary consumer (vole) is in the second trophic level
  3. the secondary consumer (barn owl) is in the third trophic level

Food chains are rarely longer than four trophic levels as energy is used up or lost at each level.

OrganismHow it gets its energy
ProducerUsing light energy to produce food by photosynthesis
Primary consumerEating producers, most are herbivores
HerbivoreEating only plants
Secondary consumerEating primary consumers, most are carnivores
CarnivoreEating 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

A vole gets its energy from eating grass, but also eats insects. This makes it both a primary and secondary consumer. Which term from the table above could be used to describe the vole?