GCSEBiologyAQARevision NotesEcologyTrophic Levels in an EcosystemPyramids of Biomass

Pyramids of Biomass (AQA GCSE Biology): Revision Note

Exam code: 8461

Written by: Lára Marie McIvor

Reviewed by: Dr Natalie Lawrence

Updated on 21 October 2026

Pyramids of biomass

Biomass is the mass of living tissues contained within an organism
It is often measured as dry mass of the organism
- How much mass the plant or animal would have without including all the water that is in the organism
Biomass decreases at each successive trophic level within a food chain

Diagram of a three-level food chain showing biomass at each trophic level. Grass is the producer at trophic level 1, with a biomass of 50 kg. An arrow leads from the grass to a grasshopper, the primary consumer at trophic level 2, with a biomass of 10 kg. An arrow leads from the grasshopper to a frog, the secondary consumer at trophic level 3, with a biomass of 2.5 kg. Biomass decreases at each successive trophic level. — **Biomass decreases along the food chain from 50 kg in the producer to 10 kg in the primary consumer and 2.5 kg in the secondary consumer**

Use this image

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 at each trophic level in a food chain
A pyramid of biomass is always a pyramid shape due to the decrease in biomass present at each trophic level

Diagram showing a four-level food chain alongside a pyramid of biomass. Clover is the producer and is eaten by a snail, the primary consumer. The snail is eaten by a thrush, the secondary consumer, which is eaten by a sparrowhawk, the tertiary consumer. Beside the food chain is a four-tier pyramid that becomes progressively narrower towards the top, representing decreasing biomass at successive trophic levels. — **A food chain and corresponding pyramid of biomass, showing that biomass decreases at higher trophic levels**

Use this image

Being able to construct accurate pyramids of biomass from appropriate data is an important skill for a biologist
Each bar shows the biomass of the whole trophic level, not of one organism
If you are given the number of organisms and the mass of one, multiply them first (e.g. 1000 chickens × 2.2 kg = 2200 kg) and plot that total

Worked Example

Below is a food chain with four trophic levels:

clover → snail → thrush → sparrowhawk

The total biomass of the organisms at each trophic level:
- clover: 80 kg
- snail: 30 kg
- thrush: 10 kg
- sparrowhawk: 2 kg

(a) Draw a pyramid of biomass for this food chain.

(b) Calculate the percentage of the biomass lost between the clover and the sparrowhawk. Give your answer to 2 significant figures.

Answer (a):

Biomass pyramid for a food chain of clover, snail, thrush and sparrowhawk. Horizontal bars are centred on a midpoint and decrease in width at each trophic level, showing decreasing biomass from clover to sparrowhawk. Annotations indicate that bars should touch, be equally spaced around the midpoint, each trophic level should be labelled, and the x-axis should use a suitable regular scale and be labelled “Biomass (kg)

Answer (b):

Step 1: recall the percentage equation

= (difference ÷ initial value) x 100

Step 2: determine the difference between the biomass of the clover and the hawk

Biomass of clover: 80
Biomass of sparrowhawk: 2

80 - 2 = 78

Step 3: enter into equation

= (78 ÷ 80) x 100

= 97.5 %

Step 4: round to two significant figures

= 98%

Examiner Tips and Tricks

When drawing pyramids of biomass to scale it is important to:

draw with a pencil and ruler
put the producer bar at the base of the pyramid
draw the scale around a mid-point of zero, and the bars symmetrically around this point
- E.g. 80 kg will be 40 kg either side of a 0 kg mid-point
choose a scale that allows the largest bar to take up more than half of the width available
label the x-axis with the quantity and its unit (e.g. biomass in kg), and label each bar once with the name of the organism – do not add extra labels (such as "tertiary consumer") that might be wrong

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