Food chains and food webs

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  • Food chains and food webs
    • Radiation from the sun is the main source of energy for all living things. The suns light energy is captured and used by green plants and algae during photo synthesis to make new biomass.
    • A number of elements are taken in by organisms
      • Carbon
      • Oxygen
      • Hydrogen
      • Nitrogen from soil
      • Magnesium (chlorophyll)
      • Potassium (growth)
    • Basic four trophic levels
      • Producer = makes food from the sun using photo synthesis (prey)
      • Primary consumer = gains energy by eating producers, these are normally herbivores (prey)
      • Secondary consumer = gains energy by eating the primary consumer, usually omnivores or carnivores (Prey/ Predator)
      • Tertiary consumer = gains energy by eating the secondary consumer, usually carnivores (Predator)
    • Energy transfer between trophic levels
      • Plants convert between 1% and 3% of the suns energy into organic matter. Most of the energy is not converted
        • 90% of the suns energy is reflected back by clouds or dust
        • Not all wavelengths can be absorbed
        • Light may not fall on a chloroplast
      • The energy that plants convert into other organic molecules is called gross production. But plants themselves only use 30% of this energy for respiration.
      • Primary consumers only use about 10% of the energy from the plant
      • Secondary and tertiary use about 20% of the energy from the prey for their own bodies
      • Because energy transfer between each trophic level is so inefficient most food chains only have about 4 or 5 levels. There is simply not enough energy to support more.


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