Cambridge O Level Biology · Syllabus 5090 · Relationships of Organisms with One Another and with the Environment
Pyramid of Energy
What is Pyramid of Energy?
A diagram in which the width of each bar represents the energy transferred at that trophic level over a period of time, for a stated area, using units such as kilojoules per square metre per year. Because energy is transferred out of the food chain at every level and is never returned, the energy transferred always decreases going up the chain, so a correctly constructed pyramid of energy is always upright. This makes it the most reliable of the three ecological pyramids for comparing energy flow between trophic levels.
This definition is part of the Relationships of Organisms with One Another and with the Environment chapter in Cambridge O Level Biology.
Examiner tips on Pyramid of Energy
- Units carry marks in this topic. Energy at a trophic level is a rate per unit area: \(\mathrm{kJ/m^2/year}\). It has to be per area, because a bigger field holds more energy, and per time, because energy keeps arriving. If a question supplies a unit, use that exact unit in your answer; if it asks you to comment on a pyramid of energy, the time component is part of why the pyramid is meaningful.
- “Which pyramid would be most useful, and why?” is a standard question, and the answer is nearly always the pyramid of energy, for a reason you must state: it measures the energy transferred over time, so it shows how much energy is actually available to the next level and it cannot be distorted by organism size or by a seasonal snapshot. Naming it without that reason scores one mark out of two.
Questions students ask about Pyramid of Energy
Can a pyramid of numbers really be upside down?
Yes. Bar width counts individuals and takes no account of size, so a single large producer such as an oak tree can support thousands of caterpillars, giving a narrow base and a much wider second level. Parasites do the same thing higher up a chain. A pyramid of energy, by contrast, is always upright when correctly constructed.