Understanding Food Webs


Ups and Downs of Food Chains

  • Organisms in a Food Chain are dependent on others.
    • Example: Grass is eaten by rabbits which are hunted and eaten by foxes.
  • Grass captures the energy from the sunlight to photosynthesise and make glucose.
  • Glucose provides energy for the plant to grow.
  • When a rabbit eats grass, the energy left in the grass is transferred to the rabbit.  The rabbit uses some of this energy to move and grow.
  • When a fox eats a rabbit the remaining energy in the rabbit is transferred to the fox.
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Changes in the Numbers of Organisms

Changes in the number of one organism in a food chain can affect other organisms in the food chain. Here are some examples how:

  • The number of plants in an ecosystem can be affected because of the amount of rain, sunlight, minerals as well as the space that is avaliable to grow.
  • The number of animals can be affeccted by the amount of food, habitats, mates, water and disease.
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Food Webs and Trophic Levels

Most animals eat many different things and are involved in many different food chains. These food chains can be put together in a Food Webwhich shows how the food chains are connected. Food webs can sometimes be very complex!

In a food web, there are different rankings. These are listed below.

  • Produces make their own food.
  • Primary Consumers eat producers
  • Secondary Consumers eat primary consumers
  • Tertiary Consumers eat secondary consumers.

These rankings are called Trophic Levels. The trophic levels of an organism is the position it occupies in a food chains.

The arrows in a Food Web indicate the Direction of the Energy Flow.

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Knock-on Effects

Harbour seals, harp seals and Artic terns all fed on Artic cod. If the Artic cod catches a disease and dies, the Artic tern and harp seals will eat more of their other prey. The harbour seal only eats Artic cod, so they will die too. This means that the cod will not eat amphipods and copepods, so there will be more food for the humpback whale and Artic char, and their populations will increase. 64701.jpg
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Key Vocab for Understanding Food Webs

  • Food chain
  • Food web
  • Primary consumer
  • Secondary consumer
  • Tertiary consumer
  • Trophic level 
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