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A pyramid of numbers shows how many organisms are at each trophic level, while a pyramid of biomass shows their total mass. 12 questions answered.
Pyramids of Biomass and Energy Transfer is part of Trophic levels in an ecosystem (biology only) in GCSE AQA Higher Biology.
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A pyramid of numbers shows how many organisms are at each trophic level, while a pyramid of biomass shows their total mass. 12 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 Pyramids of Biomass and Energy Transfer before testing yourself from memory.
Picture a massive African savanna with thousands of zebras, but only a handful of lions. Why aren't there equal numbers of predators and prey?
The answer lies in energy transfer. Every time energy moves from one organism to another, most of it is lost. This creates a pyramid structure in ecosystems that we can measure and predict.
Understanding energy flow explains why food chains rarely exceed four or five levels, and why large predators are always rare compared to their prey.
Think of biomass as the 'weight' of life at each level. Producers (plants and algae) form the wide base because they have the most biomass. Primary consumers (herbivores) form a narrower bar above them, and so on.
Unlike pyramids of numbers, pyramids of biomass are almost always pyramid-shaped. This is because biomass directly relates to the energy available at each level.
Trap: Many students confuse biomass with numbers of organisms. A single oak tree has massive biomass but counts as just one organism.
Here's a shocking fact: producers (plants and algae) only capture about 1% of the light energy that hits them. The other 99% is either reflected, transmitted through leaves, or lost as heat.
This 1% efficiency occurs because photosynthesis is a complex process with multiple energy conversion steps. Not all wavelengths of light can be used, and the biochemical reactions themselves are not 100% efficient.
Despite this low efficiency, producers still form the foundation of all food webs because the total amount of sunlight energy available is enormous.
When energy moves from one trophic level to the next, only about 10% gets transferred. The other 90% is lost through respiration, movement, heat production, and waste products.
This 10% rule explains why pyramids of biomass get narrower at each level. If plants have 1000 kg of biomass, herbivores will have roughly 100 kg, and carnivores about 10 kg.
Worked example: Calculating Energy Transfer Efficiency
A grassland has 10,000 kJ of energy stored in grass. Rabbits consume this grass and store 800 kJ. Calculate the energy transfer efficiency.
Answer: 8% efficiency
Notice this efficiency is close to 10%, which is typical for most ecosystems. The exact percentage varies, but it's rarely above 20% or below 5%.
The 90% energy loss at each trophic level happens for several reasons. Organisms use most of their energy for life processes rather than growth.
Energy is lost through: cellular respiration (producing heat), movement and activity, excretion of waste products, and parts of organisms that aren't eaten (like bones, shells, or roots).
This inefficiency limits food chain length. After 4-5 transfers, there's not enough energy left to support another trophic level.
Exam questions on energy transfer often test calculations and explanations. Here's how to maximise your marks.
Exam depth extension: In pyramids of biomass and energy transfer, connect why energy flow matters in ecosystems to what are pyramids of biomass? 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.
Common mistake: Students often confuse energy transfer with biomass transfer. Energy is measured in joules (J) or kilojoules (kJ), while biomass is measured in kilograms (kg) or grams per square metre (g/m²).
For 6-mark questions on energy flow, structure your answer as: state the efficiency percentages, explain what happens to the 'lost' energy, give specific examples of energy losses, and link this to why food chains are short.
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.
A pyramid of biomass is a diagram showing the total mass of living organisms at each trophic level in an ecosystem, drawn as horizontal bars with producers at the base. Unlike pyramids of numbers, pyramids of biomass are almost always pyramid-shaped, because biomass relates to the energy available at each level.
A pyramid of numbers shows how many organisms are at each trophic level, while a pyramid of biomass shows their total mass. A single oak tree has massive biomass but counts as just one organism, so pyramids of numbers can be oddly shaped, but pyramids of biomass are almost always pyramid-shaped.
Energy is lost between trophic levels through cellular respiration, which produces heat, through movement and activity, through excretion of waste products, and through parts of organisms that are not eaten, such as bones, shells or roots.
Producers capture only about 1% of the light energy that hits them because the other 99% is reflected, transmitted through leaves or lost as heat. Not all wavelengths of light can be used, and the reactions of photosynthesis are not 100% efficient.
The 10% rule states that only about 10% of energy is transferred from one trophic level to the next; the other 90% is lost through respiration, movement, heat and waste. So 1000 kg of plant biomass supports roughly 100 kg of herbivores and about 10 kg of carnivores.
Efficiency = (energy transferred ÷ energy available) × 100%. If grass stores 10,000 kJ and rabbits store 800 kJ, efficiency = (800 ÷ 10,000) × 100% = 8%, close to the typical 10%. Energy is measured in kJ, while biomass is measured in kg or g/m².
Of the light energy that hits producers, only about 1% is captured by photosynthesis; the other 99% is reflected, transmitted through leaves or lost as heat. Not all wavelengths of light can be used, and the reactions are not 100% efficient.
There are far fewer lions than zebras because every time energy moves from one organism to another, most of it is lost, with only about 10% transferred between trophic levels. Less energy is passed on to predators, so large predators are always rare compared to their prey.
Energy transfer efficiency between trophic levels is typically around 10%; the exact percentage varies but is rarely more than 20% or less than 5%. For example, rabbits storing 800 kJ from 10,000 kJ of grass is an 8% efficiency.
Energy is measured in joules (J) or kilojoules (kJ), while biomass is measured in kilograms (kg) or grams per square metre (g/m²). Confusing energy transfer with biomass transfer is a common mistake.
Producers are the foundation of all food webs despite capturing only about 1% of light energy, because the total amount of sunlight energy available is enormous. They capture energy from sunlight and make food for the rest of the chain.
Using the 10% rule, if plants have 1000 kg of biomass, herbivores will have roughly 100 kg and carnivores about 10 kg. This is why pyramids of biomass get narrower at each level.