Food Chains

This lesson covers: 

  1. What food chains show and how organisms depend on each other
  2. The direction of energy flow in food chains
  3. How toxins can accumulate up food chains

Food chains show feeding relationships

The feeding relationships between organisms in an ecosystem can be shown using food chains.

Illustration showing a food chain with grass, a rabbit, a snake, and an owl.

Food chains show what organisms eat and what other organisms they are eaten by - the 'who eats who' in an ecosystem.


The arrows represent the direction of energy flow from one organism to the next.

Energy passes along food chains

As one organism eats another, not all the energy is transferred to the next level in the food chain.

Diagram showing energy transfer in a food chain from grass to rabbit to snake to owl, with energy lost at each level.

Energy is lost throughout food chains because: 

  • Some energy is used by the organism for vital life processes like movement and respiration.
  • Some energy is lost to the environment as heat.


So, the further along the food chain, the less energy available to transfer to the next organism.

Toxins accumulate up food chains

If toxic substances enter at the producer level of a food chain, they can become concentrated in organisms further along.

Diagram showing toxins building up in a food chain from small organisms to larger carnivores.
  • Organisms take in the toxins when eating contaminated food organisms.
  • The toxins accumulate faster than they can be broken down or excreted.
  • So carnivores at the end of long food chains experience greater toxin build up.