food chains

• How energy passes through an ecosystem

  1. Using food chains

  2. Predator prey cycles
• Food chain


  Shows what gets eaten by what in an ecosystem
• Food chain


  • Simplified version of a food web
  • Doesn't show all interactions, just one chain
• Producer


  Photosynthetic organism like a green plant or alga
• Producer


  • Grass
• Photosynthesis


  Organism can produce glucose using the sun's energy
• Biomass


  Biological molecules incorporated into the plant
• Primary consumer


  Eats the producers
• Primary consumers


  • Rabbits
  • Mice
  • Aphids
• Secondary consumer


  Feeds on the primary consumer
• Secondary consumer


  • Owl
• Tertiary consumer


  Feeds on the secondary consumer
• As energy gets passed up the food chain levels, most of it gets lost
• If there were 1000 joules of energy in the grass, only around 100 joules might be passed on to the mice and only around 20 joules might be passed on to the owl
• The arrows between food chain levels represent the flow of energy up the chain
• Predator prey cycle


  Graph showing how the population of prey and predator vary together over time
• The change in the predator population always lags behind that of the prey
• When owl population is low

  Mouse population increases
• When mouse population is high

  Owl population increases
• When owl population gets too high

  Mouse population declines
• When mouse population declines

  Owl population declines
• The cycle repeats because it takes a long time for entire populations to increase or decrease