Biology B2 Revision: Energy Flow

Mindmap showing energy flow through food chains and how feeding relationships are represented.

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  • Energy Flow
    • Pyramids of numbers and pyramids of biomass.
      • Represent feeding relationships between organisms in a food chain or web.
      • Pyramids of biomass.
        • Show the dry mass of living material at each stage of a food chain.
          • Why might they look different to pyramids of numbers?
            • If producers are very large or a small parasite lives on a large animal.
          • Measuring dry mass difficult- involves removing all water from organisms- kills organism.
        • Show trophic levels better than a pyramid of numbers.
        • Difficult to construct
          • Dry mass kills organism
          • Some organisms may feed on organisms from different trophic levels.
    • As energy flows along food chain, some is used in growth.
      • Energy measured in Joules or Kilojoules
    • At each trophic level of a food chain, much energy is transferred into not very useful forms.
      • Heat from respiration
      • Egestion
      • Excretion
    • Material lost at each stage of the food chain is not wasted.
      • Used by decomposers which can then start another food chain.
      • 90% of the available energy can be 'lost' at each trophic level.
        • Animal at the end of the food chain does not have much food available to it.
    • Efficiency of energy transfer between trophic levels.
      • Energy used for growth/ energy input. Written as %.


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