DP Biology (first assessment 2025)

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Question 21N.2.SL.TZ0.5b

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Date November 2021 Marks available [Maximum mark: 4] Reference code 21N.2.SL.TZ0.5b
Level SL Paper 2 Time zone TZ0
Command term Describe Question number b Adapted from N/A
b.
[Maximum mark: 4]
21N.2.SL.TZ0.5b
(b)

Describe transport across cell membranes by osmosis.

[4]

Markscheme

a. form of diffusion;
b. osmosis is the movement of water molecules;
c. (movement) across a selectively/semi/partially permeable membrane/cell membrane;
d. from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)
OR
movement of water molecules from a high concentration of water to a low concentration of water molecules;
e. it is a passive transport mechanism/does not use ATP;
f. channel proteins/aquaporins are used;

Examiners report

Most gained at least 2 marks describing osmosis. Common mistakes were not making it clear whether the concentration was referring to water or to the solute. A surprising number of students did not refer to water at all.

Syllabus sections