6-5-3-efficiency-of-energy-transfers

Efficiency of Energy Transfers

• A very large proportion of the Sun’s energy is not made available to photosynthetic plants, because

  • Light falls away from plants

  • Light passes through leaves or is reflected away

  • Light is a mixture of wavelengths, and only certain wavelengths stimulate photosynthesis

• During photosynthesis, primary producers such as plants and algae convert light energy to chemical energy in biological molecules

• The storing of this chemical energy as plant biomass makes a certain amount of energy available to the next trophic level, the primary consumers

• Only a small percentage of plant biomass becomes biomass in the primary consumer because:

  • Not all the plant’s biomass is eaten by the primary consumer

  •  Not all the consumer’s biomass intake is digested

    • Think about the energy content of cow dung, which can be dried and used as a heating/cooking fuel, as it contains a lot of undigested biomass e.g. cellulose

  • The primary consumer converts a lot of chemical energy to movement and heat, and only a small amount to new biomass in its own body

• The efficiency of biomass transfer from one trophic level to the next is low, typically around 10%

Calculating efficiency of biomass transfers between trophic levels

• Given the appropriate data, it is possible to calculate the efficiency of biomass transfer from one trophic level to the next, as a percentage

Efficiency of transfer = (biomass transferred  biomass intake)  100

• Where:

  • Biomass transferred = biomass that has passed to the higher trophic level

  • Biomass intake = biomass of the lower trophic level that has been consumed

Calculating the efficiency of energy transfer between trophic levels

• A common way of working out the efficiency of energy transfer is calculating the net productivity of one trophic level as a percentage of the net productivity of the preceding trophic level