Pyramids of Biomass (AQA GCSE Biology)
Revision Note
Written by: Lára Marie McIvor
Reviewed by: Lucy Kirkham
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
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
Being able to construct accurate pyramids of biomass from appropriate data is an important skill for a biologist:
Examiner Tips and Tricks
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.
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