DP Biology (first assessment 2025)

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Question 21N.1A.SL.TZ0.13

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Date November 2021 Marks available [Maximum mark: 1] Reference code 21N.1A.SL.TZ0.13
Level SL Paper 1A Time zone TZ0
Command term Question number 13 Adapted from N/A
13.
[Maximum mark: 1]
21N.1A.SL.TZ0.13

John Cairns used the technique of autoradiography to produce photographs of DNA from the bacterium E. coli.

[Source: © Cold Spring Harbor Laboratory Press. Autoradiography of bacterium E. coli DNA - micrograph, The Chromosome of
Escherichia coli Cairns, J.P., 1963. Cold Spring Harbor Symposia, Quantitative Biology, 28(44).]

 

Which conclusion was drawn from his experiments?

A. The DNA in all organisms is circular.

B. DNA in E. coli naturally contains thymidine.

C. DNA replication is conservative.

D. The DNA in E. coli is 900 μm in length.

[1]

Markscheme

D

Examiners report

The technique developed by Cairns is part of the program in sub-topic 3.2, but answers to this question showed that relatively few candidates were familiar with it.

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