A-LevelBiologyEnzymesFeb/Mar 2021Paper 1 Q131 Mark
Catechol is a chemical found in a number of fruits. Catechol can be oxidised to a quinone by the enzyme catechol oxidase. Catechol oxidase is inhibited by parahydroxybenzoic acid (PHBA), which is structurally similar to catechol. In the presence of PHBA, the Michaelis-Menten constant (Km) for catechol oxidase increases. How does PHBA inhibit catechol oxidase? 1 PHBA and catechol can both bind to the enzyme but not at the same time. 2 PHBA is a non-competitive inhibitor of catechol oxidase. 3 PHBA decreases the Vmax of the reaction.
A1, 2 and 3
B1 only
C2 only
D3 only
✓ Correct Answer
The correct answer is B: 1 only
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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