Oxygen catches electrons at the end of the chain
- The idea
- Predict
- See it
- Why
- Check
The idea
“Oxygen combines with glucose's carbons to make CO2, the way a fire burns fuel.”
The overall equation looks like burning. Glucose and O2 go in, and CO2 and water come out. So it's easy to picture O2 grabbing the carbons.
The short version
The mistake: Oxygen combines with glucose's carbons to make CO2, the way a fire burns fuel.
What's actually true: O2 is used only at the end of the electron transport chain, as the final electron acceptor. CO2 comes from glucose's carbons.
- NADH and FADH2 carry glucose's electrons to the chain. O2 waits at the end as the final electron acceptor.
- Without O2 the chain backs up, NADH can't unload, and the Krebs cycle runs out of NAD+. So the cycle stops, though it never uses O2 itself.
On the exam: O2 never touches the fuel. It catches electrons at the end of the chain and becomes water.