food chains, predator & prey

• 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
• Photosynthesis


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


  Molecules incorporated into the plant
• Primary consumer


  Eats the producers
• Secondary consumer


  Feeds on the primary consumer
• Tertiary consumer


  Feeds on the secondary consumer
• As energy gets passed up the different levels of the food chain, most of it gets lost
• The arrows between the different levels of the food chain 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
• The predator and prey populations are out of phase with each other
• Predator prey cycle


  1. Low predator population, prey population increases

  2. Lots of prey, predator population increases

  3. High predator population, prey population declines

  4. Low prey, predator population declines
• The main reason for the predator prey cycle is that it takes a long time for entire populations to increase or decrease