DP Biology (first assessment 2025)

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Question 21M.1B.SL.TZ1.e

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Date May 2021 Marks available [Maximum mark: 3] Reference code 21M.1B.SL.TZ1.e
Level SL Paper 1B Time zone TZ1
Command term Evaluate Question number e Adapted from N/A
e.
[Maximum mark: 3]
21M.1B.SL.TZ1.e

By referring to both graphs, evaluate the hypothesis that vinblastine targets cells in mitosis and prevents them from completing the process.

[3]

Markscheme

Evaluation of evidence in graph on left

a. increase in (percentage of) cells in mitosis (as vinblastine concentration rises) ✔

b. supports hypothesis that cells get stuck in/cannot complete mitosis ✔

Evaluation of evidence in graph on right

c. drop in anaphase-metaphase ratio due to fewer cells in anaphase/more cells in metaphase ✔

d. cells not progressing from metaphase to anaphase/get stuck in metaphase ✔

Do not allow mpa if the candidate is arguing that the hypothesis is not supported.

Examiners report

This was another challenging data-analysis task with marks spread across the whole range, but full marks were rarely awarded. Many candidates thought that a rise in mitotic index had to mean that more cells were entering mitosis and they failed to deduce from the drop to zero of the anaphase-metaphase ratio that cells were getting stuck in metaphase. As in (d), it was necessary both to understand how cells progress through the cell cycle and be able to make deductions from trends in quantitative data.

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