This deep dive covers Pyramids of Biomass within Ecosystems Communities for GCSE Biology. Topic 1: Ecosystems Communities It is section 8 of 15 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.

📊 Pyramids of Biomass

A pyramid of biomass shows the total mass of living material at each trophic level in a food chain. Each bar represents the biomass (dry mass) of all organisms at that level.

Painted pyramid of biomass with four trophic levels at proper biomass-ratio scale: a wide bottom meadow of grass + wildflowers + small trees (producers, 10,000 kg), seven rabbit silhouettes (primary consumers, 1,000 kg), four fox silhouettes (foxes, 100 kg), and a single eagle (apex, 10 kg). Red ~10% arrows on the left side between each tier. A sepia parchment scroll on the right lists where the 90% biomass goes: respiration, movement, body warmth, faeces, urea.

Figure: Pyramid of biomass — each level is ~10% of the one below.

Why Is It Pyramid-Shaped?

At each trophic level, energy is lost through:

Respiration — organisms use energy for movement, growth, and keeping warm
Waste products — not all food is digested (faeces, urine)
Heat — energy transferred to the surroundings

Only about 10% of the biomass at one level is passed to the next. This means there is always less biomass at higher trophic levels — which is why the diagram forms a pyramid shape.

Pyramids of Biomass vs Pyramids of Numbers

Pyramids of numbers can sometimes look inverted (e.g. one oak tree → thousands of caterpillars), but pyramids of biomass are almost always pyramid-shaped because biomass accounts for the size of organisms, not just how many there are.

Exam tip: If asked why biomass decreases at each trophic level, always mention respiration and waste/egestion — these are the two mark points examiners look for.

Pyramids of Biomass