Grade 11 · Biology
Energy flow & trophic levels
Why it matters
Food chains, food webs, pyramids and the 10% rule.
Core20m readingPrerequisite: None
How does energy flow through an ecosystem?
Short answer
Energy enters an ecosystem as sunlight, is captured by producers through photosynthesis, and flows to consumers as they eat one another along a food chain. At each trophic level only about 10% of the energy is passed on; the rest is lost mostly as heat. Because energy is not recycled, ecosystems need a continual input from the Sun.
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Frequently asked questions
- What is the 10% rule?
- Only about 10% of the energy at one trophic level is passed to the next; the rest is used for life processes or lost as heat.
- Why are food chains usually short?
- Because so much energy is lost at each level, there is rarely enough left to support more than four or five trophic levels.