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Biomass is the total mass of living organisms in a given area, and a pyramid of biomass shows it at each trophic level. Free notes and 10 questions answered.
Understanding Pyramids of Biomass is part of Trophic levels in an ecosystem (biology only) in GCSE AQA Higher Biology.
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GCSE AQA Higher
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Biomass is the total mass of living organisms in a given area, and a pyramid of biomass shows it at each trophic level. Free notes and 10 questions answered.
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Use this lesson to stay inside Trophic levels in an ecosystem (biology only) while connecting the detail back to the wider Ecology topic.
Read the core explanations from Understanding Pyramids of Biomass before testing yourself from memory.
Picture a grassland ecosystem. Thousands of grass plants support hundreds of rabbits, which feed dozens of foxes. This isn't random - there's a mathematical reason why ecosystems stack up like pyramids.
When we measure the total mass of living organisms at each level, we get a pyramid of biomass. The grass (producers) at the bottom has the largest biomass, rabbits (primary consumers) have less, and foxes (secondary consumers) have the least.
Trap: Many students think pyramids of biomass can be inverted like pyramids of numbers. They can't - biomass pyramids are always pyramid-shaped because energy is lost at each transfer.
Biomass gives us a snapshot of how much living material exists at each level. Unlike counting individual organisms, biomass accounts for size differences - one elephant has more biomass than a thousand ants.
Trophic levels are always numbered starting from the bottom: Level 1 = producers (plants), Level 2 = primary consumers (herbivores), Level 3 = secondary consumers (carnivores), and so on.
Only about 10% of energy transfers from one trophic level to the next. The other 90% is lost as heat during respiration, movement, and waste production. This energy loss explains why biomass decreases at each level.
Because organisms need energy to build biomass, less available energy means less biomass can be supported. This is why you never see more foxes than rabbits in a stable ecosystem.
Exam questions often give you biomass data and ask you to draw the pyramid. The key is getting the proportions right and labelling everything correctly.
Worked example: Constructing a Pyramid of Biomass
Draw a pyramid of biomass using this data: Grass = 2000 g/m², Grasshoppers = 200 g/m², Birds = 20 g/m²
Answer: A three-level pyramid with grass (2000 g/m²) at bottom, grasshoppers (200 g/m²) in middle, birds (20 g/m²) at top, all properly labelled with trophic levels.
Common mistake: Students often make all bars the same width. The width must be proportional to the biomass values - this is what makes it a pyramid shape.
You might wonder why we use biomass instead of just counting organisms. Pyramids of numbers can be misleading - one oak tree might support thousands of insects, creating an inverted pyramid.
Pyramids of biomass give a more accurate picture because they account for the actual mass of living material. A single oak tree has much more biomass than the insects it supports, so the pyramid shape is maintained.
Pyramid of biomass questions are mark-friendly if you know the technique. Examiners look for specific things: correct proportions, proper labelling, and understanding of trophic levels.
Exam depth extension: In understanding pyramids of biomass, connect why food chains form pyramids to understanding biomass and trophic levels using clear cause-and-effect statements. When you explain biological processes, include what changes, why it changes, and the consequence for cells, organisms, or populations. If calculations appear, show each step, include units, and end with a sentence that interprets the result in biological context.
Mark-winning phrases: Use 'trophic level' not just 'level', always include units (g/m²), and write 'producers' not just 'plants' when describing level 1.
Master these pyramid construction skills and you'll find these questions become straightforward mark-earners in your exam.
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-20.
Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Biomass is the total mass of living organisms in a given area or volume, measured in grams per square metre (g/m²) or kilograms per hectare (kg/ha). Unlike counting organisms, biomass accounts for size differences: one elephant has more biomass than a thousand ants.
To draw a pyramid of biomass, put producers (trophic level 1) at the bottom and draw a horizontal bar for each level, with widths proportional to the biomass. For grass 2000 g/m², grasshoppers 200 g/m² and birds 20 g/m², dividing by 200 gives bars of 10, 1 and 0.1 units; label each with its organism, value and units.
A pyramid of numbers can be inverted because it counts organisms, not their mass: one oak tree might support thousands of insects. A pyramid of biomass gives a more accurate picture because the single oak tree has much more biomass than the insects it supports.
Pyramids of biomass are pyramid-shaped because only about 10% of energy transfers from one trophic level to the next, with the other 90% lost as heat during respiration, movement and waste. Organisms need energy to build biomass, so less energy means less biomass can be supported at each level.
Biomass is measured in grams per square metre (g/m²) or kilograms per hectare (kg/ha). Units should always be included on pyramids of biomass for full marks.
A pyramid of biomass cannot be inverted the way a pyramid of numbers can; it is always pyramid-shaped because energy is lost at each transfer. A single oak tree has much more biomass than the insects it supports.
To make bars proportional, divide each biomass value by the smallest value: for grass at 2000 g/m², grasshoppers at 200 g/m² and birds at 20 g/m², the bars are 10, 1 and 0.1 units wide. Bars must be centred and their widths proportional, not all the same.
Biomass is used instead of counting organisms because it accounts for size differences, since one elephant has more biomass than a thousand ants. Pyramids of numbers can be misleading, for example one oak tree supporting thousands of insects.
Trophic level 1, the producers, always goes at the bottom of a pyramid of biomass, with primary consumers at level 2 and secondary consumers at level 3 on top. Producers have the largest biomass.
A pyramid of biomass needs each bar labelled with the organism name and its biomass value with units, such as g/m², plus 'Trophic level 1, 2, 3' on the left. Using 'producers' rather than 'plants' for level 1 and 'trophic level' rather than just 'level' gains marks.