# Electron transport chain

A line of proteins in the inner mitochondrial membrane. NADH and FADH2 hand over electrons, which flow down the chain to oxygen. Energy released pumps protons across the membrane.

Biology (university) · Part 03: Respiration and photosynthesis · Card 4 of 8 · Last updated 2026-10-19

## Analogy

A water wheel line where each drop of the fall pumps water uphill into a reservoir.

## In practice

Oxygen is the final electron acceptor. That is why you must breathe it in.

## Practice

### Flashcards

- **What is the final electron acceptor in respiration?** Oxygen, which becomes water.

### Interview questions

**Outline the stages of aerobic respiration and say where each occurs and what it produces.**

- Glycolysis in cytoplasm: 2 ATP, 2 NADH
- Citric acid cycle in matrix: NADH, FADH2, CO2
- Electron transport and chemiosmosis in inner membrane: most ATP
- Oxygen is final electron acceptor

**Explain how a proton gradient makes ATP in mitochondria.**

- Electron flow pumps protons into intermembrane space
- Gradient stores potential energy
- Protons flow through ATP synthase
- Flow drives ADP plus phosphate into ATP

## Questions people ask

### Why do we need to breathe oxygen?

Oxygen is the final electron acceptor. It takes electrons at the end of the chain and combines with protons to make water. Without it, electrons pile up, the chain stops and the proton gradient collapses. Cells then lose most of their ATP supply within minutes.

### What does cyanide do to the body?

Cyanide binds to an enzyme complex at the end of the electron transport chain, called cytochrome c oxidase. Electrons cannot reach oxygen, so the chain stops. Cells run out of ATP even though oxygen is present. Tissues with high energy needs, such as the brain and heart, fail first.

## Related concepts

- [Chemiosmosis](https://studyvisually.com/learn/science/biology-university/biology-university-part-3/biology-university-part-3-concept-5)
- [Glycolysis](https://studyvisually.com/learn/science/biology-university/biology-university-part-3/biology-university-part-3-concept-2)
- [Citric acid cycle](https://studyvisually.com/learn/science/biology-university/biology-university-part-3/biology-university-part-3-concept-3)
- [Redox reaction](https://studyvisually.com/learn/science/biology-university/biology-university-part-3/biology-university-part-3-concept-1)

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