Energy Transfers



  • biological mass in an ecosystem at any given time
  • presence of varying amounts of water makes measurements unreliable
  • must measure dry/carbon mass in small samples
  • samples must be small as the samples must be killed
  • measured in grams per square meter for flat sample areas (gm-2)
  • measured in grams per cubic meter for aquatic environments (gm-3)
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  • 1 calorie = amount of energy required to raise the temperature of one gram of water by 1•C 
  • sample of dry mass is weighed
  • sample is burned in pure oxygen in a sealed chamber (bomb)
  • burning needs a reactor and ignition source


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Energy Flow

  • is insufficient
  • over 90% of the sun's energy is reflected
    • deflected by dust/particles/clouds
    • absorbed by the atmosphere

  • not all wavelengths can be absorbed by leaves
  • lightwave (photon) may not be hitting the chlorophyll molecule
  • carbon dioxide and other factors limit photosynthesis
  • 1-3% of light is fixed by photosynthesis
    • 20-50% is used for respiration
    • remaining is used for biomass
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Energy Efficiency

  • measured in percentage of energy efficiency
  • between trophic levels
  • measured per m2 per year
    • Kj m-2 year-1
    • kilojoules per meter-squared per year
  • (energy after transfer/energy before transfer) x 100
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Gross Primary Production

  • measure of energy productivity
  • GPP
  • total quantity of chemical energy store in biomass
    • in area/volume
  • before respiration/other factors
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Net Primary Production

  • NPP = GPP - R
  • chemical energy in plants' biomass after respiratory losses
  • lose energy to the environment
  • available to the organism for growth, reproduction, repair of tissues/organs
  • available for other organisms
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Net Production of Consumers


  • I = chemical energy of ingested food
  • only 10% is transferred from plants to primary consumers
  • only 20% is transferred from primary to secondary consumers

Energy Loss

  • faeces and urine (F)
  • respiration and heat (R)
  • movement, growth and reproduction (R)
  • not eaten/digested (F)


NPC = I - (F + R)

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