Explain why the pyramid of energy is always upright. State the limitations of ecological pyramids.

1. 1 · Define in one line. A pyramid of energy shows the energy at each trophic level in a given time, or per year per unit area.
2. 2 · Give the reason. At each transfer some energy is lost as heat, so every higher level has less energy than the one below.
3. 3 · Show it with numbers. For example: producers 20,000 J → herbivores 2,000 J → carnivores 200 J → top carnivores 20 J.
4. 4 · Draw the pyramid. [Four bars labelled producers, herbivores, carnivores and top carnivores, with energy values and heat-loss arrows]
5. 5 · State the limitations.
   • Ignore a species at two or more trophic levels.
   • Assume a simple food chain; cannot show a food web.
   • Give no place to saprophytes.
6. 6 · Link to real life. Eating cereals and pulses directly uses solar energy better than eating animals fed on them.
7. 7 · Close in one line. So the energy pyramid is the most reliable of the three, but all pyramids simplify nature.

Scoring tip: Write 'lost as heat at each step' in your reason. 'Energy decreases' alone does not earn the mark.