AQA GCSE Biology

Revision Notes

7.4.2 Pyramids of Biomass

Pyramids of Biomass

Biomass

  • Biomass is the mass of living tissues (or recently dead tissues that have not yet been decomposed) that a plant or animal is made up of
    • For example, the wood of a recently fallen tree is still biomass, even though the organism is no longer alive
  • It is the ‘dry mass’ of the organism (how much mass the plant or animal would have without including all the water that is in the organism)
  • There is always less and less biomass as you move up through the trophic levels in a food chain or food web
  • For example, for the simple food chain below, if we added up the total biomass of all the grass in this particular ecosystem, it would be greater than the total biomass of all the grasshoppers, which would in turn be greater than the total biomass of all the frogs

Food chain showing biomass, downloadable IGCSE & GCSE Biology revision notes

Biomass always decreases as you move up through the trophic levels in a food chain or food web

Pyramids of biomass

  • A food chain can be represented as a type of modified bar chart called a pyramid of biomass
  • A pyramid of biomass shows the relative biomass (mass of living or recently dead material) at each trophic level in a food chain
  • A pyramid of biomass is always a pyramid shape (as seen in the image below)
  • For example, the pyramid of biomass below shows that the total biomass of clover plants is greater than the total biomass of snails, which is greater than the total biomass thrushes, which is greater than the total biomass of sparrowhawks

A pyramid of biomass, IGCSE & GCSE Biology revision notes

A pyramid of biomass

  • Being able to construct accurate pyramids of biomass from appropriate data is an important skill for a biologist:

 

Worked example constructing a pyramid of biomass_1, downloadable IGCSE & GCSE Biology revision notes

Worked example constructing a pyramid of biomass_2, downloadable IGCSE & GCSE Biology revision notes

Worked example constructing a pyramid of biomass_3, downloadable IGCSE & GCSE Biology revision notes

Exam Tip

As there is always less and less biomass as you move up through the trophic levels in a food chain, pyramids of biomass are always pyramid-shaped: the higher the trophic level the smaller the bar will be.

Remember: trophic level 1 organisms (producers) are at the bottom of the pyramid. The next bar up is primary consumers, the next is secondary consumers and so on up the food chain.

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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