| Date | May 2012 | Marks available | 1 | Reference code | 12M.1.SL.TZ1.9 |
| Level | Standard level | Paper | Paper 1 | Time zone | Time zone 1 |
| Command term | Outline | Question number | 9 | Adapted from | N/A |
Question
What occurs during DNA replication?
A. DNA polymerase separates the two DNA strands.
B. DNA molecules containing nucleotides from the original molecule are produced.
C. Adenine forms a base pair with either thymine or uracil.
D. New bases attach to the original sugar-phosphate backbone.
Markscheme
B
Examiners report
Although this question was only an average discriminator, almost as many candidates picked option A as those who chose the correct answer, B. Also a large number picked D. There was a concern expressed by some teachers that C was a correct answer because RNA primers formed during DNA replication have uracil paired with adenine in the template DNA strand. In fact this was the least popular answer and candidates can reasonably have been expected to choose answer B as the best response. Substantial numbers of candidates chose A and D, showing weak understanding of replication. It is felt that students need to understand and be able to apply the concepts of semi-conservative replication, rather than simply committing the points to memory.
