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Date November 2019 Marks available 1 Reference code 19N.3.HL.TZ0.3
Level Higher level Paper Paper 3 Time zone TZ0 / no time zone
Command term Predict Question number 3 Adapted from N/A

Question

An experiment was carried out to study osmosis in plant cells. Small cylinders of zucchini (Cucurbita pepo) were cut and placed in different sucrose solutions at 25 °C. The figure shows the percentage changes in mass after 24 hours.

Estimate the solute concentration of the zucchini cells.

[1]
a.

If a zucchini is allowed to dry in the open air, predict how the osmolarity of the zucchini cells would change.

[1]
b.

Explain one reason for calculating the percentage changes in mass.

[2]
c.

Predict what would happen to a red blood cell placed in distilled water.

[1]
d.

Markscheme

0.36 mol dm-3/M ✔

Units required
Allow a range of 0.35–0.37 mol dm-3/M.

a.

osmolarity will increase «because the cells become dehydrated»
OR
the cells become hypertonic ✔

Accept water potential of the tissue decreases.
Do not accept "change" instead of "increase".

b.

a. the change in mass indicates whether the tissue has gained/lost water ✔

b. the pieces of tissue will not all be the same mass «at the beginning of the experiment» ✔

c. to compare the relative changes in mass ✔

c.

a. water would move into the red blood cells ✔

b. it would lyse
OR
swell
OR
burst ✔

d.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.
[N/A]
d.

Syllabus sections

Core » Topic 1: Cell biology » 1.4 Membrane transport
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Core » Topic 1: Cell biology
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