(a) Write the word equation for anaerobic respiration in human muscle cells. [1]
(b) Write the word equation for anaerobic respiration in yeast. [2]
(c) Give one disadvantage of anaerobic respiration compared with aerobic respiration. [1]
- (a) glucose → lactic acid; reject if oxygen, carbon dioxide or water is shown; ignore 'energy' as a product(1)
- (b) glucose → ethanol; accept alcohol; ignore 'energy' as a product; reject if oxygen is shown as a reactant(1)
- (b) carbon dioxide (accept CO₂) shown as the second product; marks are independent, e.g. glucose → carbon dioxide alone scores this mark only(1)
- (c) releases much less energy / less ATP (per glucose); accept lactic acid builds up / causes oxygen debt / fatigue / produces toxic products (lactic acid or ethanol)(1)
- Answer: (a) glucose → lactic acid (b) glucose → ethanol + carbon dioxide (c) much less energy released
- Examiner tip: Lactic acid in muscles has no carbon dioxide — adding CO₂ to the muscle equation loses the mark.