• During photosynthesis, primary?producers?(such as plants and algae) convert light energy into chemical energy in biological molecules
• Gross primary production?(GPP) can be defined as the amount of chemical energy stored in the carbohydrates within plants (during photosynthesis)
  • In other words, the quantity of energy stored in the glucose produced represents the gross primary production

   

• Net primary production?(NPP) refers to the amount of energy available to herbivores in the plant’s biomass?after plant respiratory losses
  • Of total energy trapped in glucose during photosynthesis, 90% of this energy will be released from glucose to create ATP for the plant
  • The plant uses most of its glucose to fuel active cellular processes
  • A significant percentage of the energy originally captured will not be used to create new plant cells and therefore will not be able to be passed on to herbivores via eating

   

• The?chemical energy?that is?leftover?in a plant after respiratory loss is known as the?net primary production (NPP)
• Net primary production can therefore be calculated using the equation below:

NPP = GPP - R

• This means that NPP, like GPP, is expressed in units of?energy per unit area or volume, for example:
  • Using area: J m–2?(joules per square metre)
  • Using volume: J m–3?(joules per cubic metre)

   

• NPP is important because it represents the energy that is available to organisms at?higher trophic levels?in the ecosystem, such as?primary consumers?(herbivores and omnivores) and?decomposers

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Net primary production (NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account

Net primary productivity

• Net primary productivity?is expressed using units of energy/mass per unit area?per unit time
  • Time must be included as it is a?rate

   

• For example
  • Mj m–2?y-1?(megajoules per square metre per year)
  • kg km-2y-1?(kilograms per square kilometre per year)