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Food chains and cycles


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Food chains show the feeding relationships between living things. Pyramids of biomass reveal the mass of living material at each stage in a chain. The amount of material and energy decreases from one stage to the next. Carbon moves from the atmosphere into living species and back into the atmosphere in a cycle that is crucial to life on Earth.

Decay processes

Decay is an essential life process that digests food or waste matter and recycles materials. Materials from living things decay because they are digested (broken down) by microorganisms. These microorganisms cause decay by releasing enzymesenzymes: Proteins which catalyse or speed up chemical reactions inside our bodies that break down compounds to be absorbed by their cells.

Bacteria and fungi are the main groups of decomposerdecomposer: An organism which eats dead organisms or animal droppings, and breaks them down into simple materials..

Factors affecting decay

The factors that affect the rate of decay include:

  • moisture
  • temperature
  • amount of available oxygen.

Microorganisms are more active and digest materials faster when they are in moist, warm and aerobic conditions. They will digest materials more slowly in dry, cold and anaerobicanaerobic: Without oxygen. conditions.


Some of the substances released during decay are needed by plants for healthy growth. In a stable community of living things, processes that return substances to the environment (such as decay) are balanced by the processes that remove and use substances. In this way, the substances are continuously recycled.


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