Explain why a yeast cell producing ethanol is still described as carrying out cellular respiration, and compare this process to aerobic respiration in terms of oxygen use and products formed.

AQA GCSE Biology (8461) — 4.4.2 Respiration · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Yeast cells can survive in conditions where oxygen is absent, such as at the bottom of a dough mixture.

Model answer (4 marks)

Cellular respiration is an exothermic reaction that releases energy, so both aerobic and anaerobic processes give up energy for the cell.

In aerobic respiration oxygen is the final electron acceptor; in anaerobic respiration it is not used.

Aerobic respiration produces carbon dioxide and water as the end‑products.

Anaerobic respiration in yeast produces ethanol and carbon dioxide, but no water.

Examiner tips

  • Use the word ‘exothermic’ to show energy release. Mention oxygen as the key difference. State the products for each process. Keep each point short and to the point.

Common mistakes

  • Confusing anaerobic respiration with fermentation. Saying yeast produces only water. Forgetting to mention that both processes release energy.

Mark scheme (4 marks)

  1. Cellular respiration is an exothermic reaction that releases energy / energy is released in both processes
  2. Aerobic respiration requires / uses oxygen; anaerobic respiration does not use oxygen
  3. Aerobic respiration produces carbon dioxide and water
  4. Anaerobic respiration in yeast produces ethanol and carbon dioxide (not water)

Key terms in this question

cellular respiration · aerobic respiration

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