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Date May 2019 Marks available 1 Reference code 19M.3.SL.TZ2.2
Level Standard level Paper Paper 3 Time zone Time zone 2
Command term Estimate Question number 2 Adapted from N/A

Question

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]
a.

Determine, with a reason, the nucleotide base that was marked with radioactivity.

Base:

Reason:

 

 

[2]
b.

Markscheme

0.45 «mm» ✔

Allow values between 0.35 «mm» and 0.50 «mm»

a.

a. thymine / T ✔

b. because only in DNA / not in RNA ✔

b.

Examiners report

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.

a.

Few were able to name thymine as the base or give a reason it was used in the experiment.

b.

Syllabus sections

Core » Topic 3: Genetics » 3.2 Chromosomes
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