DP Biology (first assessment 2025)

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Question 20N.1A.SL.TZ0.5

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Date November 2020 Marks available [Maximum mark: 1] Reference code 20N.1A.SL.TZ0.5
Level SL Paper 1A Time zone TZ0
Command term Question number 5 Adapted from N/A
5.
[Maximum mark: 1]
20N.1A.SL.TZ0.5

How many chromosomes are there in a cell during anaphase of mitosis, if the diploid number of the cell is 20?

A. 10

B. 20

C. 40

D. 80

[1]

Markscheme

C

Examiners report

Some candidates were caught out by this question, either because their understanding of mitosis had weaknesses or because they did not think carefully enough. In anaphase, the two sister chromatids that have made up each chromosome in prophase and metaphase have separated. Guidance in sub-topic 1.6 of the program indicates that they should be referred to as chromosomes as soon as separation has occurred, rather than as chromatids. In anaphase there are therefore double the diploid number of chromosomes in a cell. Cytokinesis will subsequently halve the number, so the daughter cells are diploid.

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