Food Chains

All organisms need energy to live. Sun is the primary source of energy on Earth. Energy is transferred from one organism to the next through a food chain.

A food chain is a sequence of organisms in which one is eaten by the next member in the chain, whilst a trophic level describes the position of a species in a food chain (The Physics Teacher, 2018). For example,

1st trophic level            second                         third                            fourth

(producer)     (primary consumer)  (secondary cons)        (tertiary consumer)

hawthorn         ->        caterpillar        ->        robin               ->        hawk

Rosebush        ->        greenfly           ->       ladybird           ->        sparrow  ® hawk

Grass               ->        rabbit              ->       fox

Bramble (blackberry) ->   field mouse   ->  badger

Dead leaves ->  woodlouse  ->   spider
 

Pyramid of numbers is a diagram describing the numbers of organisms at each stage in a food chain.

The numbers normally reduce as you move up the pyramid because of high energy loss (about 90% in respiration as heat, excretion and decay) at each trophic level and because organisms usually increase in size as you move up a pyramid and need to feed on a greater number. This limits the length of a food chain (4 or 5 steps).

Pyramids of numbers are limited because the size of the organisms can alter the standard shape or it may not be possible to represent large numbers of organisms correctly (The Physics Teacher, 2018).

Limitations of Pyramid of Numbers:

  • Does not take into account the actual numbers of organisms involved
  • Cannot be drawn to scale
  • Some are not technically pyramids – they are inverted (Leaving Cert Biology, 2018)

A food web consists of two or more interlinked food chains.

Nutrient recycling is the way in which elements (such as carbon and nitrogen) are transferred between living and non-living components of an ecosystem.

Honeybee
Courtesy of the EPA

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