The flow of energy
Show on a big screenA producer stores 10,000 joules (J) of energy. How much reaches the third level?
- Level 1 stores 10,000 J.
- About a tenth passes on: level 2 gets 1,000 J.
- Level 3 gets about a tenth of that: 100 J.
- Level 4 gets about a tenth again: 10 J.
Drag the energy at level 1. Watch each level.
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The rule
About 100 J reaches the third level. A tenth passes on at each step.
The ten per cent law.
On average, only about a tenth passes to the next level. The rest is spent staying alive, or lost as heat. It cannot be gathered back into food.
Energy flows one way. It does not return to the producer, or to a lower level.
A tenth means 10 out of every 100. Take a smaller producer that stores 5,000 J. A tenth of 5,000 J is 500 J. So level 2 gets about 500 J. A tenth of 500 J is 50 J. So level 3 gets about 50 J. A tenth of 50 J is 5 J. So level 4 gets about 5 J. This shrinking is why food chains have few levels.
| Level | Energy | About a tenth of |
|---|---|---|
| 1 — producer | 10,000 J | — |
| 2 — herbivore (eats plants) | 1,000 J | level 1 |
| 3 — carnivore (eats animals) | 100 J | level 2 |
| 4 — top carnivore (the last link) | 10 J | level 3 |
Try the lab to finish this lesson.