Food Chains & Food Webs (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

• A food chain shows the transfer of energy from one organism to the next, starting with a producer
• The source of all energy in a food chain is light energy from the Sun
• The arrows in a food chain show the transfer of energy from one trophic level to the next
• Energy is transferred from one organism to another by ingestion (eating)
• In the food chain above:

Food Webs

• A food web is a network of interconnected food chains
• Food webs are more realistic ways of showing connections between organisms within an ecosystem as animals rarely exist on just one type of food source

A food web shows the interdependence of organisms

• Food webs give us a lot more information about the transfer of energy in an ecosystem
• They also show interdependence - how the change in one population can affect others within the food web
• For example, in the food web above, if the population of earthworms decreased:
  • The population of grass plants would increase as there are now fewer species feeding off them
  • The populations of frogs and mice would decrease significantly as earthworms are their only food source
  • The population of sparrows would decrease slightly as they eat earthworms but also have another food source to rely on (caterpillars)

• Most of the changes in populations of animals and plants happen as a result of human impact - either by overharvesting of food species or by the introduction of foreign species to a habitat
• Due to interdependence, these can have long-lasting knock-on effects to organisms throughout a food chain or web