# Fermentation

Making ATP without oxygen by recycling NADH back to NAD+, so glycolysis can keep going. Humans make lactate. Yeast makes ethanol and carbon dioxide.

Biology (university) · Part 03: Respiration and photosynthesis · Card 6 of 8 · Last updated 2026-10-19

## Analogy

A backup generator: low output, but it keeps the lights on.

## In practice

Sprinters feel muscle burn as lactate builds up. Yeast fermentation makes bread rise and beer fizzy.

## Practice

### Flashcards

- **Why does fermentation make lactate or ethanol?** To turn NADH back into NAD+ so glycolysis can continue without oxygen.

## Questions people ask

### Why do muscles produce lactate?

During hard exercise, muscles need ATP faster than oxygen can arrive. Glycolysis speeds up, and fermentation recycles NAD+ by turning pyruvate into lactate. This gives a quick but small supply of ATP. The lactate is later carried to the liver and turned back into glucose.

### How much ATP does fermentation produce?

Only the 2 ATP made in glycolysis, per glucose. Full aerobic respiration makes about 30, so fermentation is roughly 15 times less efficient. Cells that depend on fermentation must therefore break down a lot more glucose to get the same energy, which is why anaerobic activity cannot last long.

## Related concepts

- [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)
- [Electron transport chain](https://studyvisually.com/learn/science/biology-university/biology-university-part-3/biology-university-part-3-concept-4)
- [Chemiosmosis](https://studyvisually.com/learn/science/biology-university/biology-university-part-3/biology-university-part-3-concept-5)

Web page: https://studyvisually.com/learn/science/biology-university/biology-university-part-3/biology-university-part-3-concept-6
Study this card in the app: https://studyvisually.com/app/learn?category=biology-university&card=biology-university-part-3-concept-6