# A baker uses yeast to make bread dough rise. The yeast is mixed into the dough and left in a warm place. After some time, bubbles of gas are produced and the dough expands. Explain why the dough rises, including the name of the process responsible and the conditions inside the dough that cause this process to occur.

> Pearson Edexcel A-Level Biology A (9BI0) — 4.1 Cellular respiration · Explain · 5 marks

> Yeast are single-celled fungi that can respire both aerobically and anaerobically. When mixed into bread dough, the yeast cells are surrounded by flour, water and sugar.

## Mark scheme (5 marks)

1. The yeast respires anaerobically (inside the dough)
2. There is little/no oxygen available inside the dough (so aerobic respiration cannot occur)
3. Sugar/glucose is broken down (by the yeast)
4. Carbon dioxide is produced (as a product of anaerobic respiration in yeast)
5. The carbon dioxide gas causes the dough to expand/rise (by forming bubbles)

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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-uses-yeast-to-make-c3d76c51) · Published by Druglandscape Ltd.