# Explain why anaerobic cell respiration produces far less ATP per glucose molecule than aerobic cell respiration.

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

## Mark scheme (4 marks)

1. In aerobic respiration, pyruvate (and acetyl groups) are fully oxidised / broken down to CO₂ and water, releasing much more energy for ATP synthesis.
2. In anaerobic respiration, pyruvate is only partially oxidised / converted to lactate or ethanol and CO₂, so much of the potential chemical energy in glucose remains locked in these products.
3. Aerobic respiration re-oxidises NADH (and FADH₂) via the electron transport chain, generating a large proton gradient that drives ATP synthesis by chemiosmosis, yielding the majority of ATP.
4. In anaerobic respiration, the electron transport chain is not used / NADH is re-oxidised by reducing pyruvate instead, so ATP is produced only from substrate-level phosphorylation in glycolysis (net 2 ATP per glucose).

## Key terms

- [anaerobic cell respiration](https://www.gradenine.co.uk/glossary/anaerobic-cell-respiration)
- [aerobic cell respiration](https://www.gradenine.co.uk/glossary/aerobic-cell-respiration)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-anaerobic-cell-respiration-produces-4a1b74bd) · Published by Druglandscape Ltd.