| Date | May 2010 | Marks available | 1 | Reference code | 10M.1.SL.TZ2.12 |
| Level | Standard level | Paper | Paper 1 | Time zone | Time zone 2 |
| Command term | Analyse | Question number | 12 | Adapted from | N/A |
Question
The graph below shows the effect of temperature on the separation of the strands in DNA to form single strands. The temperature at which 50% of the DNA is single-stranded is called the melting temperature (TM).
What do the results show?
A. When the temperature reaches 85°C there are no more double-stranded DNA molecules.
B. When the temperature reaches 85°C the DNA strands start separating rapidly.
C. A TM of 85°C means that DNA is not stable at room temperature (25°C).
D. The separation of the DNA strands is directly proportional to the increase in temperature.
Markscheme
B
Examiners report
This question turned out to be an easy question. According to the teacher comments, this was due to the fact that candidates were able to rule all the incorrect answers out. There is however, a lot of interesting data in this question.
The TM is extremely important in PCR and it is interesting to see that at a given temperature the DNA strands all of a sudden tend to separate. This is also a good question to use with candidates to explain the breaking of H bonds between complementary bases.
