Efficiency of energy transfers

• Efficiency of Energy Transfers


  The proportion of the Sun's energy that is made available to photosynthetic plants
• Reasons why a large proportion of the Sun's energy is not made available to photosynthetic plants

  • 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
• Photosynthesis


  1. Primary producers such as plants and algae convert light energy to chemical energy in biological molecules

  2. The storing of this chemical energy as plant biomass makes a certain amount of energy available to the next trophic level the primary consumers
• Reasons why only a small percentage of plant biomass becomes biomass in the primary consumer

  • Not all the plant's biomass is eaten by the primary consumer
  • Not all the consumer's biomass intake is digested
  • 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

  1. Efficiency of transfer (biomass transferred / biomass intake) x 100

  2. Biomass transferred: biomass that has passed to the higher trophic level

  3. Biomass intake: biomass of the lower trophic level that has been consumed
• Worked example: Blackberry bush and aphids


  • Blackberry bush mass: 35 kg
  • Aphid mass: 4.1 kg
  • Efficiency of energy transfer = (4.1 / 35) x 100 = 11%
• Calculating the efficiency of energy transfer between trophic levels

  1. Efficiency of energy transfer = (net productivity of primary consumers / net productivity of producers) x 100

  2. Efficiency of energy transfer = (net productivity of secondary consumers / net productivity of primary consumers) x 100

  3. Net productivity of producers (NPP) = GPP - R

  4. Net productivity of consumers = N = 1 - (F + R)
• Worked example: Wheat farmer and toads


  • Toads ingest 10,000 kJ/m2/yr
  • Toads lose 2,000 kJ/m2/yr in faeces and urine
  • Toads lose 7,000 kJ/m2/yr through respiration
  • Net productivity of toads = 10,000 - 9,000 = 1,000 kJ/m2/yr
  • Efficiency of energy transfer = (1,000 / 10,000) x 100 = 10%
• How human activities can manipulate the transfer of biomass through ecosystems


  • For producers (arable farmers): Providing artificial light, optimising planting distances, irrigation, use of fertilisers, selective breeding, use of fungicides/pesticides, fencing, ploughing and herbicides, growing crops that store energy in edible forms
  • For primary consumers (livestock farmers): Use of good quality feeds/food supplements, use antibiotics and vaccines, control predation, reduce competition for grazing, indoor husbandry
• Exam questions can refer to biomass and energy interchangeably. The biomass of an organism is effectively a measure of how much chemical energy is stored within it.