# Explain why lactate fermentation allows glycolysis to continue during intense exercise despite the absence of sufficient oxygen.

> IB DP Biology Higher Level (2023 syllabus) — C1.2 Cell respiration · Explain · 4 marks

> During intense exercise, skeletal muscle cells can experience a temporary shortage of oxygen relative to their energy demands. Despite this, ATP production continues for a short period through anaerobic pathways.

## Mark scheme (4 marks)

1. Glycolysis requires NAD⁺ as an electron/hydrogen acceptor to oxidise glucose (or glyceraldehyde-3-phosphate), and NAD⁺ is continually consumed (reduced to NADH) during glycolysis.
2. When oxygen is insufficient, the electron transport chain cannot accept electrons from NADH, so NADH cannot be reoxidised to NAD⁺ by oxidative phosphorylation.
3. Lactate dehydrogenase converts pyruvate to lactate, simultaneously oxidising NADH back to NAD⁺ (regenerating NAD⁺).
4. The regenerated NAD⁺ allows glycolysis to continue, sustaining a small but rapid net yield of 2 ATP per glucose molecule.

## Key terms

- [lactate fermentation](https://www.gradenine.co.uk/glossary/lactate-fermentation)
- [glycolysis](https://www.gradenine.co.uk/glossary/glycolysis)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-lactate-fermentation-allows-glycolysis-9047efb0) · Published by Druglandscape Ltd.