Question 19M.3.SL.TZ2.2
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.SL.TZ2.2 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Determine, Estimate | Question number | 2 | Adapted from | N/A |
Cairns’ technique was used in an experiment to measure the length of DNA in the Chinese hamster (Cricetulus griseus). Fibroblast cells were grown with radioactive nucleotides. The DNA autoradiogram obtained is shown.
[Source: © Joel A. Huberman and Arthur D. Riggs]
Estimate the length of the molecule of DNA shown in the autoradiogram between the two arrows.
……………...mm
[1]
0.45 «mm» ✔
Allow values between 0.35 «mm» and 0.50 «mm»
This question concerned Cairns’ technique to measure the length of a section of DNA. Most candidates could estimate the length of DNA shown in the diagram.
Determine, with a reason, the nucleotide base that was marked with radioactivity.
Base:
Reason:
[2]
a. thymine / T ✔
b. because only in DNA / not in RNA ✔
Few were able to name thymine as the base or give a reason it was used in the experiment.