# Bread dough rises when yeast is added to a flour and water mixture. Explain why the dough rises, including the role of respiration in this process.

> AQA A-Level Biology (7402) — 3.5.2 Respiration · Explain · 5 marks

> Bread makers add yeast to a mixture of flour and water. After a period of time in a warm environment, the dough swells and increases in volume.

## Mark scheme (5 marks)

1. Yeast carries out anaerobic respiration
2. Glucose is broken down / used as a reactant
3. Carbon dioxide is produced as a product of anaerobic respiration in yeast
4. Ethanol / alcohol is also produced (alongside carbon dioxide)
5. Carbon dioxide gas gets trapped in the dough and causes it to expand / rise

## Related

- [Revision notes for AQA A-Level Biology (7402)](https://www.gradenine.co.uk/learn)
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