Describe how yeast is used in bread-making and explain why the bread rises during this process.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Yeast is added to the dough, where it carries out anaerobic respiration. The glucose in the flour is converted into energy, carbon dioxide and alcohol. The carbon dioxide is trapped in the dough, forming bubbles that expand the dough and make the bread rise. The alcohol produced evaporates during baking.
Examiner tips
- Use the word "anaerobic respiration" and mention "glucose" as the substrate.
- Explain that CO₂ forms bubbles that expand the dough.
- Note that alcohol evaporates during baking to avoid extra points.
- Keep the answer concise and use correct terminology.
Common mistakes
- Forgetting to mention anaerobic respiration or CO₂ production.
- Saying the bread rises because of yeast alone, without linking to CO₂.
- Including unnecessary details such as yeast strain or fermentation time.
Mark scheme (4 marks)
- Yeast carries out anaerobic respiration (in the dough)
- Carbon dioxide is produced (as a product of anaerobic respiration)
- The carbon dioxide causes the bread to rise (by forming bubbles / expanding the dough)
- Alcohol is also produced but evaporates (during baking)
Key terms in this question
Related
- All Pearson Edexcel International GCSE Biology (4BI1) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →