Net Primary Production (AQA A Level Biology): Revision Note
Exam code: 7402
Net primary production
Net primary production (NPP) can be defined as
the chemical energy stored in plant biomass after respiratory losses to the environment have been taken into account
Plants convert light energy to chemical energy in the form of glucose during photosynthesis; the total energy stored in this way is gross primary production (GPP)
Some of the energy stored during GPP is lost to the environment, e.g. when waste heat is generated during respiration
The energy that remains in the plant tissues after these energy losses is the NPP
NPP is important because it represents the energy that is available to consumers in the ecosystem
Net primary production can therefore be calculated as follows:
NPP = GPP - R
Where:
GPP = gross primary production
R = respiratory loss to the environment
NPP, like GPP, is expressed as energy per unit area or volume, e.g.:
J m–2
J m–3
Examiner Tips and Tricks
Remember that GPP is the total energy transferred during photosynthesis, while NPP is the energy that remains after any energy losses during respiration.
Note that the concept of NPP applies only to producers, and not to animals, so the NPP equation only includes respiratory loss, and not losses in faeces and urine.
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