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A-LevelBiologyEnzymesFeb/Mar 2025Paper 1 Q151 Mark

Succinic dehydrogenase is an enzyme that catalyses the conversion of succinate to fumarate in aerobic respiration. Malonate is a reversible inhibitor of succinic dehydrogenase. Malonate reduces the enzyme’s activity by binding to its active site. Malonate and succinate cannot bind to the active site at the same time. Which statement describes the effect of malonate on the activity of succinic dehydrogenase?

AIn the presence of malonate, Vmax can still be reached if the concentration of succinate is increased.
BMalonate has no effect on the Km.
CIn the presence of malonate, Vmax can still be reached if the concentration of fumarate is increased.
DMalonate decreases the Km.

✓ Correct Answer

The correct answer is A: In the presence of malonate, Vmax can still be reached if the concentration of succinate is increased.

📋 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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About This A-Level Biology Question

Topic

This multiple-choice question tests Enzymes in A-Level Biology (syllabus code 9700). It is worth 1 mark.

Source

This question appeared in the Cambridge A-Level Biology Feb/Mar 2025 examination, Paper 1 Variant 2.

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