Pyramids of Number Biomass Energy IGCSE Biology

Pyramids of Number, Biomass and Energy: Comparing Trophic Levels

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

Key concept

Pyramids of number show the number of organisms at each trophic level. Pyramids of biomass show the total dry mass. Pyramids of energy show the rate of energy transfer. Only pyramids of energy are always a true pyramid shape.

Students must be able to draw, label and interpret all three types of ecological pyramid. The most common exam errors are inverted bars and failing to explain why pyramids of number can have unusual shapes while energy pyramids cannot.

Pyramids of number

A pyramid of numbers shows the number of organisms at each trophic level. The producer bar is at the bottom, and each consumer level is stacked above. Usually, each bar is smaller than the one below because it takes many prey organisms to support fewer predators.

However, pyramids of number can be inverted or have unusual shapes. For example, one oak tree (producer) supports thousands of caterpillars. The tree bar would be very small and the caterpillar bar very large. Similarly, one animal can host many parasites, giving an inverted top bar.

Pyramids of biomass

A pyramid of biomass shows the total dry mass of organisms at each trophic level at a given time. It avoids the size problem of number pyramids because one large tree has a much greater biomass than one caterpillar.

Pyramids of biomass are usually pyramid-shaped because energy is lost at each level, so less biomass can be supported at higher levels. However, in aquatic ecosystems, they can occasionally be inverted because phytoplankton (producers) reproduce so rapidly that their standing biomass at any one time is less than the zooplankton feeding on them.

Pyramids of energy

A pyramid of energy shows the rate of energy flow (measured in kJ per m² per year) through each trophic level. It is always pyramid-shaped because energy is inevitably lost as heat through respiration at every level. No trophic level can contain more energy than the one below it over time.

Pyramids of energy are considered the most accurate representation of energy flow through an ecosystem, but they are the hardest to measure because they require data collection over time, not just a snapshot.

Drawing pyramids correctly

When drawing ecological pyramids:

1. Always label each bar with the trophic level or organism name.
2. Draw bars centrally aligned, not left-aligned.
3. The width of each bar should be proportional to the value it represents.
4. The producer bar is always at the bottom.
5. Include units where numerical data is given (number of organisms, g/m², kJ/m²/year).

Try a focused question (3 marks)

Explain why a pyramid of energy is always pyramid-shaped but a pyramid of numbers is not.

Show the answer and marking guidance

Energy is lost as heat through respiration at every trophic level, so less energy is always available at higher levels.
A pyramid of numbers shows the count of organisms, which can be distorted by organism size.
For example, one large tree (one organism) can support many caterpillars, producing an inverted pyramid of numbers but not an inverted pyramid of energy.

Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.

Common mix-ups to avoid

Check these points against your own answer before moving on.

Drawing pyramids with the top consumer at the bottom.
Saying pyramids of energy can be inverted (they cannot).
Confusing biomass with number of organisms.
Not labelling trophic levels or organisms on the pyramid bars.