Trophic Levels (AQA A Level Biology): Revision Note

Energy from net primary production

• The energy remaining in the tissues of plants after respiratory loss is known as net primary production (NPP)

• NPP is available for:

  • plant growth and reproduction

  • transfer to consumers at other trophic levels when plant biomass is eaten by herbivores or broken down by decomposers

Net production of consumers

• Consumers are organisms that gain energy from the tissues of other organisms

• When a consumer ingests the tissues of another organism, the stored chemical energy is either:

  • transferred to the consumer's tissues, where it is stored as chemical energy

  • lost to the environment

• The energy that is transferred to the tissues of consumers is the net production of consumers

  • This is also known as secondary production

• The net production of consumers (N) can be calculated as follows:

N = I - (F + R)

• Where:

  • I = the chemical energy in ingested food

  • F = the chemical energy lost to the environment in faeces and urine

  • R = the respiratory losses to the environment

• Energy is lost in the form of faeces and urine because:

  • consumers are not able to digest all of the food they eat, so some is egested as faeces

    • E.g. consumers may not digest all of the cellulose in plant matter, or the fur and bones of animal prey

  • energy may be stored in the bonds of excess amino acids, which are converted into urea for excretion in the urine

• Energy is lost during respiration in the form of heat, which is radiated into the environment