Describe how yeast is used in bread-making and explain how the process causes dough to rise.

Cambridge International IGCSE Biology (0610) — 21.2 Biotechnology · Describe · 4 marks · View as Markdown

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 metabolises glucose anaerobically.
1. The yeast cells consume glucose as a substrate.
2. During anaerobic respiration the glucose is converted into ethanol and carbon dioxide.
3. The released CO₂ forms bubbles within the dough matrix.
4. These bubbles expand the dough, making it rise and giving bread its light texture.

Examiner tips

Use the word ‘anaerobically’ to show understanding of yeast metabolism.
Mention both ethanol and CO₂ as products to demonstrate full knowledge.
Explain that CO₂ bubbles expand the dough to show the link between the process and the result.

Common mistakes

Forgetting to state that yeast works anaerobically.
Only naming CO₂ and omitting the role of glucose as a substrate.
Not linking the CO₂ bubbles to the rise of the dough.

Mark scheme (4 marks)

Yeast respires anaerobically (in the dough)
Glucose is broken down / used as a substrate by yeast
Carbon dioxide is produced / released
Bubbles of carbon dioxide form inside the dough, causing it to rise

Key terms in this question

yeast