Explain why anaerobic cell respiration produces a much smaller yield of ATP per glucose molecule than aerobic cell respiration.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Aerobic respiration fully oxidises glucose to CO₂ and H₂O, releasing the maximum amount of energy that can be harnessed to produce ATP. In contrast, anaerobic respiration only partially oxidises glucose – it stops at lactate (in animals/bacteria) or ethanol + CO₂ (in yeast). The chemical energy that remains in these end‑products is not captured as ATP. Aerobic respiration also uses the electron transport chain and oxidative phosphorylation in the inner mitochondrial membrane, which generates the bulk of the ATP (≈30–32 per glucose). Anaerobic respiration relies only on glycolysis, yielding just 2 ATP per glucose. Hence the ATP yield is far smaller in anaerobic respiration.
Examiner tips
- Mention the complete vs. partial oxidation of glucose
- State the end‑products of anaerobic respiration
- Explain the role of the electron transport chain
- Give the ATP numbers (2 vs. 30–32)
Common mistakes
- Confusing anaerobic with aerobic respiration terminology
- Failing to mention the electron transport chain
- Giving an incorrect ATP yield for anaerobic respiration
Mark scheme (4 marks)
- Aerobic respiration fully oxidises glucose / breaks glucose down completely to carbon dioxide and water, releasing more energy for ATP synthesis.
- Anaerobic respiration only partially oxidises glucose, producing lactate (in animals/bacteria) or ethanol and carbon dioxide (in yeast), so much of the chemical energy remains in these products.
- Aerobic respiration uses the electron transport chain / oxidative phosphorylation on the inner mitochondrial membrane to generate the majority of ATP, which is absent in anaerobic respiration.
- Anaerobic respiration yields only 2 ATP per glucose (from glycolysis alone), whereas aerobic respiration yields approximately 30–32 ATP per glucose.
Key terms in this question
anaerobic cell respiration · aerobic cell respiration
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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