A-LevelBiologyNucleic acids and protein synthesisFeb/Mar 2017Paper 1 Q261 Mark
Meselson and Stahl investigated DNA in bacteria. They grew bacteria in a medium with only heavy nitrogen, 15N, until all of the bacterial DNA contained only heavy nitrogen. These bacteria were then moved from the heavy nitrogen medium and cultured in a medium with only light nitrogen, 14N. Some bacteria were collected from each of the next three generations and their DNA was analysed. Hybrid DNA contains both heavy and light nitrogen. Which row shows the correct DNA of the first and third generations? [Table 26.1]
Aall hybrid half hybrid, half light
Ball hybrid one quarter hybrid, three quarters light
Chalf hybrid, half heavy one quarter hybrid, three quarters light
Dhalf hybrid, half light one quarter hybrid, three quarters light
✓ Correct Answer
The correct answer is B: all hybrid one quarter hybrid, three quarters light
📋 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.
🔒
Unlock the Examiner's Analysis
Sign up for free to reveal the full examiner report, trap analysis, and mark scheme breakdown for this question.
Sign Up Free to Unlock →Join thousands of Cambridge students already using Oracle Prep