Ecological Productivity (Edexcel International A Level (IAL) Biology): Revision Note

Ecological Productivity

• During photosynthesis organisms such as plants convert light energy into chemical energy stored in biological molecules

  • Organisms that do this are known as producers 

• The rate at which producers convert light energy into chemical energy is known as primary productivity

• Gross primary productivity, or GPP, can be defined as the rate at which light energy is converted into chemical energy in carbohydrates during photosynthesis

• Net primary productivity, or NPP, is the GPP minus plant respiratory losses

  • A large proportion of the energy stored in glucose during photosynthesis is released from glucose to create ATP for the plant during respiration

  • This energy is therefore not stored as new plant biomass and is not available to be passed on to herbivores, also known as primary consumers

• The NPP can therefore be defined as the rate at which energy is stored in plant biomass

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

• Net primary productivity can be calculated using the equation

NPP = GPP - R

Net primary productivity, or NPP, is the rate at which energy is stored in plant biomass and made available to primary consumers.

Calculation of Ecological Productivity

• Net primary productivity can be calculated using the equation

NPP = GPP - R

• Where

  • NPP = net primary productivity; the rate at which light energy is stored in plant biomass

  • GPP = gross primary productivity; the rate at which light energy is converted into carbohydrates during photosynthesis

  • R = respiratory losses; the carbohydrates used up by the plant that are not stored in plant biomass

• NPP is expressed in units of energy per unit area or volume per unit time e.g.

  • Using area: J m^–2 yr^-1 (joules per square metre per year)

  • Using volume: J m^–3 yr^-1 (joules per cubic metre per year)

    • Volume would be used when calculating NPP in aquatic habitats