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The relationship between plants, animals and the environment is called ecology.

A simple way to view ecology is as a series of interconnected food chains. Each food chain is a linked series of living things, each of which is the food for the next in line in the chain. Pollution may destroy one or more components causing species higher up the food chain to starve or species lower down the food chain to overpopulate. Ecosystems consist of species within trophic levels or stages in a food chain These trophic levels can be divided into:

  • Producers
  • Primary consumers
  • Secondary consumers
  • Tertiary consumers
  • Detritivores


A simple food chain


These are mainly plants with some bacteria and protists such as. Protozoa, which produce their own nutrients using sunlight. Should these organisms, which are sensitive to pollutants, be eliminated everything else would starve.


Primary consumers or herbivores feed directly on living producers. Secondary consumers, or carnivores, feed on living primary consumers. Tertiary consumers, also carnivores, feed on living secondary consumers. Omnivores eat everything and so may be at any or all of these levels.

Detritivores, sometimes called decomposers, feed only on dead organisms and the waste products of living organisms, but eventually all the producers and consumers will end up in the detritivores area. They take in complex organic materials and break them down into simpler components, some of which they use, and others which they release into the environment. Eventually these simple components will become available to be taken up again by the producers, so completing the loop.

Most ecosystems are much more complicated than those described above since they contain some organisms that feed at different levels in different situations or at different stages of their lifecycle.


A simple aquatic food chain