# A baker adds yeast to a bread dough mixture and leaves it in a warm place. After one hour, the dough has risen and smells slightly of alcohol. Explain why the dough rises and why alcohol is produced during this process.

> WJEC GCSE Biology (Wales) — 1.2.1 Aerobic and anaerobic respiration · Explain · 4 marks

## Mark scheme (4 marks)

1. Yeast carries out anaerobic respiration (in the absence of oxygen / when oxygen runs out)
2. Glucose is broken down / used as a reactant in anaerobic respiration
3. Carbon dioxide is produced / released as a product of anaerobic respiration
4. The carbon dioxide gas causes the dough to rise / expands gas bubbles in the dough; alcohol (ethanol) is also produced as a product of anaerobic respiration in yeast

## Key terms

- [yeast](https://www.gradenine.co.uk/glossary/yeast)

## Related

- [Revision notes for WJEC GCSE Biology (Wales)](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/a-baker-adds-yeast-to-a-af1976b6) · Published by Druglandscape Ltd.