Energy flow – ecosystems

  • recall that in any ecosystem, plants synthesise organic compounds from atmospheric, or aquatic, carbon dioxide
  • explain that most of the sugars synthesised by plants are used by the plant as respiratory substrates, the rest are used to make other groups of biological molecules and that these biological molecules form the biomass of
    the plants
  • recall that biomass can be measured in terms of mass of carbon or dry mass of tissue per given area (to include that the chemical energy store in dry biomass can be estimated using calorimetry)
  • define gross primary production (GPP) as the chemical energy store in plant biomass, in a given area or volume
  • define net primary production (NPP) as the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account, i.e. NPP = GPP – R (where NPP represents net primary production, GPP represents gross production and R represents respiratory losses to the environment)
  • recall that net primary production is available for plant growth and reproduction, and is also available to other trophic levels in the ecosystem, such as herbivores and decomposers
  • calculate net production of consumers (N), such as animals, as:  N = I – F + R (where I represents the chemical energy store in ingested food, F represents the chemical energy lost to the environment in faeces and urine and R represents the respiratory losses to the environment)
  • define primary and secondary productivity as the rate of primary or secondary production, respectively. It is measured as biomass in a given area in a given time eg kJ ha–1 year–1