Energy and Ecosystems

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  • Energy and Ecosystems
    • Energy Transfer
      • Plants are producers
      • Energy is indigestible material is decomposed and is returned into the ecosystem
      • Not all light energy is used by plants:
        • Different wavelengths
        • Light may not fall on chlorophyll molecule
        • 90% reflected back into space
        • CO2 may limit photosynthesis
      • Not all energy is transferred to next trophic level
        • Indigestible material
        • Thermal energy is lost during respriation
      • Gross productivity= how much energy that the plant converts to organic matter
        • Net productivity= 10% = biomass
          • Net = Gross - Respiratory Losses
        • Energy transfer= energy available after / energy available before x 100
    • Pyramid Diagarams
      • Area of block = size of trophic level
      • Number
        • Don't account for size of an organism
      • Biomass
        • Dry mass= kgm-2
        • Fresh mass is easy to access but varying amount of water make this unreliable
        • Seasonal differences aren't apparent, one moment in time
        • Amount of plankton is very small at any moment as they have a short life span and reproduce very quickly
      • Energy
        • kJm-2year-1
        • Most accurate of energy flow
        • 2 organisms with same biomass may store different amounts of energy
    • Intensive ecosystems vs natural
      • Natural hasn't been changed by human activity
      • Intensive farming controls biotic and abiotic factors to make it more favourable for organisms
        • Warm, resitricted movement, high energy food
        • More food in short time at low cost
      • Crops or livestock have greater net productivity
        • Restricted energy loss from movement and recovering from disease
        • More energy input, more energy available for growth
      • Energy input to intensive farms may be greater
      • Controlling conditions= more biomass
    • Pest control
      • Pests are organisms that competes with humans for food or space
      • Chemical Pesticides
        • Fungicides kill fungi which damage crops. Crops use less energy on fighting infection and more for growth
        • Killing pests means less biomass is lost from crops so greater productivity
        • May affect non target species, bioaccumulation, can be expensive
      • Biological Control
        • Natural predators
        • Parasites, Pathonogenic bacteria or viruses- produce toxins
        • May become pests themselves, affect non target species, less cost effective, slower acting
      • Intergrated Pest Systems
        • Both chemical and biological
        • Productivity increased, costs reduced if one method is particularly expensive
        • Less pesticides used so better for environment
    • Fertilisers
      • Nitrates added to sil, more energy for higher efficiency
      • Natural = organic matter, artificial =inorganic e.g ammonium nitrate
      • Fertilisers washed into rivers, fish and plants die because of eutrophication
      • Too much of a nutrient harms plants
      • Excess fertiliser is washed away = waste of money


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