Identify and describe What Is a Pyramid of Biomass?, Shape of the Pyramid and Why Is Only ~10% of Biomass Transferred? in the context of pyramids of biomass.
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GCSE Biology Revision
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GCSE Biology revision
Pyramids of biomass
Trophic levels in an ecosystem (biology only)
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Explain the relationships between What Is a Pyramid of Biomass?, Shape of the Pyramid and Why Is Only ~10% of Biomass Transferred? and how they contribute to pyramids of biomass.
Apply and analyse knowledge of What Is a Pyramid of Biomass?, Shape of the Pyramid and Why Is Only ~10% of Biomass Transferred? to interpret unfamiliar information about pyramids of biomass.
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What Is a Pyramid of Biomass?
- A pyramid of biomass is a diagram that shows the total biomass (mass of living organisms) at each trophic level in a food chain.
- Each bar in the pyramid represents a trophic level, such as producers, primary consumers, secondary consumers, and tertiary consumers.
- An example food chain could be: grass rabbits snakes hawks, with each organism occupying a different trophic level.
Shape of the Pyramid
- The bars in a pyramid of biomass get smaller as you move up the trophic levels, showing that total biomass decreases at each level.
- Even if individual organisms at a higher level are larger (e.g. a snake is heavier than a rabbit), there are far fewer of them, so the total biomass is still lower.
- The decreasing bar sizes reflect the loss of biomass and energy as it is transferred up the food chain.
Why Is Only ~10% of Biomass Transferred?
- On average, only about 10% of the biomass from one trophic level is passed on to the next, meaning roughly 90% is lost at each stage.
- Organisms do not consume every part of their prey — for example, a hawk would not eat a snake's skeleton or teeth, so that biomass is never transferred.
- Some consumed material cannot be fully digested and is egested as faeces, meaning it never enters the consumer's body.
- The most significant reason for biomass loss is that most absorbed nutrients are used in respiration to release energy for everyday functions, rather than for growth.
- Waste products from respiration, such as carbon dioxide and urea, carry biomass out of the organism rather than storing it for the next consumer.
Trophic Levels and Biomass Loss
- A producer such as grass forms the base of the pyramid with the greatest total biomass in the food chain.
- Each successive trophic level — primary consumer, secondary consumer, tertiary consumer — holds significantly less total biomass than the one below it.
- Because biomass is lost at every transfer, long food chains become increasingly inefficient at supporting organisms at the top.
Calculating the Efficiency of Biomass Transfer
- The efficiency of biomass transfer can be calculated using the equation: Efficiency = (biomass transferred to next level) / (biomass available at previous level) × 100 For example, if rabbit biomass is 144 kg and snake biomass is 15 kg, the efficiency is (15) / (144) × 100 = 10.4%.
- If snake biomass is 15 kg and hawk biomass is 1.6 kg, the efficiency is (1.6) / (15) × 100 = 10.7%.
- These calculations confirm that roughly 10% of biomass is transferred between trophic levels, consistent with the general rule.
Key Vocabulary to Remember
- Biomass refers to the total mass of living organisms at a given trophic level, usually measured in kilograms (kg).
- A trophic level describes the position an organism occupies in a food chain, from producer up to tertiary consumer.
- Respiration is the key process responsible for most biomass loss, as organisms break down nutrients to release energy for life processes.
- Egestion is the removal of undigested material as faeces, which accounts for some of the biomass that is not passed on to the next level.