Energy Conversions

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•  The percentage of ingested energy converted to biomass is dependent upon the respiration rate

Ecological production (or productivity) refers to the rate of generation of biomass in an ecosystem

  • It is usually expressed in units of mass per area per time (e.g. kg m–2 day–1)

Biomass is the total dry weight of organic matter in organisms or ecosystems

  • Biomass is essentially the entirety of all biologically produced organic matter (e.g. proteins, carbohydrates, etc.)

The percentage of energy that is converted into biomass is dependent upon a number of factors:

  • Energy is lost as inedible materials – such as bones, teeth and hair
  • Energy is lost via excretion of undigested and unabsorbed materials
  • Energy is lost as heat from cellular respiration (higher respiration rate results in more heat lost)

Primary Production

Primary production describes the production of chemical energy in organic compounds by producers

  • The main source of energy for primary production is sunlight, but a fraction may be driven by chemosynthesis by lithotrophs

Primary production may be categorised as one of two types:

  • Gross primary production (GPP) is the amount of chemical energy as biomass that a producer creates in a given length of time
  • Net primary production (NPP) is the amount of chemical energy that is not consumed by respiration (NPP = GPP – respiration)

Secondary Production

Secondary production describes the generation of biomass by heterotrophic organisms (consumers)

  • This biomass generation is driven by the transfer of organic compounds between trophic levels via feeding
  • Secondary production may also be categorised according to gross (total) and net (usable) amounts of biomass

Ecological Productivity


Practice Question

question The total solar energy received by a grassland is 5 x 105 kJ m–2 year–1.
The gross production is 4.35 x 103 kJ m–2 year–1.
The net production of the grassland is 1.95 x 103 kJ m–2 year–1.
A: Calculate the percentage of solar energy converted into chemical energy by photosynthesis.
B: Calculate the energy lost by plant respiration.