AQA GCSE Biology

Revision Notes

7.4.3 Transfer of Biomass

Biomass Transfer

  • Energy flows from the Sun to the first trophic level (producers) in the form of light
  • Producers convert light energy into chemical energy
    • This occurs during photosynthesis, when producers convert carbon dioxide and water into glucose and oxygen
  • Producers use this glucose (during respiration) to produce their own biomass
    • Biomass is a store of chemical energy
  • When primary consumers consume (eat) producers, they break down the biomass of the producer (digestion) and use the chemical energy to increase or sustain their own biomass
  • When secondary consumers consume (eat) primary consumers, they break down the biomass of the primary consumer (digestion) and use the chemical energy to increase or sustain their own biomass, and so on
  • In this way, as chemical energy is transferred from one trophic level to the next, biomass is also transferred

Loss of Biomass

  • Not all biomass is transferred from one trophic level to the next
  • Approximately, only 10% of the biomass of each trophic level is passed on to the next
  • This is why food chains are rarely made up of more than six trophic levels – the total amount of biomass available eventually becomes too small to support another trophic level

Loss of biomass along a food chain, downloadable IGCSE & GCSE Biology revision notes

Biomass is lost at each trophic level for several reasons

  • Losses of biomass are due to:
    • Organisms rarely eat every part of the organism they are consuming – some of the biological material of plants and animals may be inedible (eg. many predators do not consume the bones of their prey)
    • Not all the ingested material is digested and absorbed, some is egested as faeces
    • Some absorbed material is lost as waste:
      • Carbon dioxide and water are waste products of respiration (when glucose is used by an organism to provide energy for moving and keeping warm, rather than to produce more biomass)
      • Water and urea are the waste products in urine, which is produced when proteins are broken down

Ways in which biomass is lost, downloadable IGCSE & GCSE Biology revision notes

Approximately, only 10% of the biomass (from the grass) eaten by this horse will get turned into new horse biomass and be available to the next trophic level

Efficiency of Biomass Transfers

  • Being able to calculate the efficiency of biomass transfers between trophic levels by percentages is an important skill for a biologist:

 

Worked example calculating efficiency of biomass transfers_1, downloadable IGCSE & GCSE Biology revision notes

Worked example calculating efficiency of biomass transfers_2, downloadable IGCSE & GCSE Biology revision notes

Exam Tip

You will be provided with the equation for calculating the efficiency of biomass transfers in the exam so don’t worry about learning it. Instead, make sure you learn how to use the equation.

It is just like working out a percentage as you would normally: divide the smaller number by the bigger one and then multiply the answer by one hundred!

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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