Pearson Edexcel · GCSE · Biology
Course version: 1BI0 · Version from Sept 2016
9.8B Calculate the efficiency of energy transfers between trophic levels…
Full specification wording
Topic 9 – Ecosystems and material cycles: 9.8B Calculate the efficiency of energy transfers between trophic levels and percentage calculations of biomass
Efficiency compares the energy or biomass passed to the next trophic level with the energy or biomass available at the level below.
Checked against the Pearson Edexcel 1BI0 specification (opens in a new tab) on .
- Point 8 of 18
Study notes
From the checked teaching notes for this specification point.
The idea
Efficiency compares the energy or biomass passed to the next trophic level with the energy or biomass available at the level below. Express it as a percentage: divide the energy (or biomass) transferred by the energy (or biomass) available at the lower level, then multiply by 100. For example, if producers hold 20 000 kJ and primary consumers contain 2 000 kJ, efficiency is (2 000 ÷ 20 000) × 100 = 10%. The same method works for biomass in grams or kilograms, provided both values use the same unit. A result near 10% is typical because most energy is lost as heat and in waste. Always keep units consistent and check the answer is below 100%, since transfer cannot exceed the energy available.
What earns the marks
- Efficiency = (energy transferred to next level ÷ energy available at previous level) × 100, giving a percentage.
- The same formula applies to biomass: (biomass at higher level ÷ biomass at lower level) × 100.
- A worked example: 2 000 kJ transferred from 20 000 kJ available gives (2 000 ÷ 20 000) × 100 = 10%.
- Efficiency is always less than 100% because energy is lost as heat and in waste materials.
Common mistakes and how to put them right
Dividing the lower level by the higher level.
Put it right: Divide the energy transferred (higher level) by the energy available (lower level).
Forgetting to multiply by 100.
Put it right: The fraction must be multiplied by 100 to give a percentage.
Mixing units, such as grams and kilograms, before dividing.
Put it right: Convert both values to the same unit first.
Reporting an efficiency above 100%.
Put it right: Transfer cannot exceed the energy available, so recheck the calculation.
Exam tips
- Write the formula first, then substitute values, so the method is clear even if arithmetic slips.
- Show the division and the multiplication by 100 as separate steps to gain method credit.
- Check the answer is a sensible percentage below 100% and state the unit as a percentage.
Try the lesson
The start of the Topic 9 – Ecosystems and material cycles: 9.8B Calculate the efficiency of energy transfers between trophic levels and percentage calculations of biomass lesson, made from checked teaching notes for this specification point.
Have a go first
A primary consumer receives 400 kJ of energy from the producer trophic level. It transfers 40 kJ of energy to the next trophic level. Calculate the efficiency of this energy transfer.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Topic 9 – Ecosystems and material cycles: 9.8B Calculate the efficiency of energy transfers between trophic levels and percentage calculations of biomass
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge