A-LevelBiologyNucleic acids and protein synthesisFeb/Mar 2021Paper 1 Q221 Mark
Which statements about complementary base pairing are correct? 1 Cytosine forms two hydrogen bonds with guanine. 2 Purines and pyrimidines are different sizes. 3 Adenine forms the same number of hydrogen bonds with thymine as it does with uracil. 4 The base pairs in a molecule of DNA are of equal length and equal width.
A1, 2 and 3
B1, 2 and 4
C1, 3 and 4
D2, 3 and 4
✓ Correct Answer
The correct answer is D: 2, 3 and 4
📋 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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