Used energy turns into heat
- The idea
- Predict
- See it
- Why
- Check
The idea
“When a cell or animal uses energy, the energy is gone.”
We talk about burning energy and losing it up a food chain, so it sounds like it disappears. It just leaves as heat.
The short version
The mistake: When a cell or animal uses energy, the energy is gone.
What's actually true: Energy is never destroyed. When an organism uses it, the energy changes form, and much of it leaves as heat.
- Energy changes form, but it is never created or destroyed. That's the first law of thermodynamics.
- No energy transfer in a cell is fully efficient. Respiration and the reactions ATP powers all release heat.
- Heat spreads out, and no organism can turn it back into food energy. That's why energy flows one way through an ecosystem.
On the exam: Energy is never used up. When it's used or lost, ask where it went. The answer is usually heat.