Draw and interpret an energy pyramid
An energy pyramid represents energy available or transferred at trophic levels over a stated area and time.
Section B18.2 · Food chains and food webs
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Read energy-transfer arrows and distinguish energy from matter in the 19.1 Energy flow pathway.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What should set each energy-pyramid bar width?
What you will learn
- Draw an energy pyramid with proportional bars
- Interpret energy values using consistent units and time intervals
Represent energy through trophic levels
An energy pyramid shows the energy at or transferred through each trophic level in a food chain. Label producers at the base and consumers above. Use a consistent area and time basis, such as kJ m⁻² year⁻¹ when provided, and make each bar width proportional to its energy value.
Energy pyramids are upright in a valid feeding pathway because less energy is available at each successive trophic level. Some energy is transferred to the environment and some organic material is not consumed or assimilated. Do not confuse energy flow with the standing mass in a biomass pyramid.
Read values and units carefully
If an energy value is given for each level, use the same scale for every bar and preserve the units. A level’s energy value is not a count of organisms or mass. An energy pyramid can compare how energy moves through feeding levels over the specified time, rather than giving a one-time population snapshot.
The diagram is a model. It does not by itself explain every cause of energy transfer or the exact efficiency unless data are supplied.
Sources for this lesson
Pause and explain
Why is a valid energy pyramid upright?
Worked example
A food chain has 12 000, 1 800 and 270 kJ m⁻² year⁻¹ at producer, primary and secondary levels. Describe its pyramid.
Show the worked solution
- Keep producers at the base.
- Make bar widths proportional to 12 000, 1 800 and 270 on one scale.
Answer The producer bar is widest, the primary consumer bar narrower and the secondary consumer bar narrowest. Label the energy and common area/time units.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Values are 20 000, 3 000 and 450 kJ m⁻² year⁻¹ from producers upwards. State the relative widths.
Give me a hint
Use one proportional scale and preserve the order.
Compare my reasoning
- 20 000 is the largest value.
- 3 000 is smaller and 450 is smallest.
Use the widest base for producers, a narrower primary-consumer bar and the narrowest secondary-consumer bar, proportional to 20 000:3 000:450.
Look for these in your work
- Largest value at base
- Widths proportional
One level is reported in kJ m⁻² year⁻¹ and another in kJ m⁻² day⁻¹. What should be done before drawing a proportional pyramid?
Give me a hint
Compare a common time basis.
Compare my reasoning
- Convert values to a common time interval.
- Then use a single area and energy scale.
Convert the energy values to the same time basis and confirm the area basis before comparing bar widths.
Look for these in your work
- Units checked
- Comparable basis stated
A learner labels an energy pyramid’s width “number of fish.” Explain the correction.
Give me a hint
Match the label to the represented measure.
Compare my reasoning
- An energy pyramid shows energy, not fish counts.
- Counts may be represented by a number pyramid.
Label each width with the energy value and its unit; use a numbers pyramid if the intended data are fish counts.
Look for these in your work
- Measure corrected
- Alternative identified
Common mistakes
- Using counts or mass as the bar width
- Mixing energy values with different time or area units
- Drawing higher trophic levels wider than lower ones in a valid energy pyramid
What can you explain now?
What should set each energy-pyramid bar width?
Compare with the explanation
Energy represented at that trophic level on a common basis
The width is proportional to the energy value.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
What measure does an energy pyramid represent, and why must its area and time basis be consistent?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.