DP Biology (first assessment 2025)

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Question 19N.2.SL.TZ0.b.ii

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Date November 2019 Marks available [Maximum mark: 3] Reference code 19N.2.SL.TZ0.b.ii
Level SL Paper 2 Time zone TZ0
Command term Explain Question number b.ii Adapted from N/A
b.ii.
[Maximum mark: 3]
19N.2.SL.TZ0.b.ii

Explain how water is used in photosynthesis.

[3]

Markscheme

a. water is split/broken «up»/lysed/undergoes photolysis ✔ For mpa, reject “water is cut in half”. For mpa, accept photolysis only if the context shows that water is being split.

b. producing/providing electrons ✔

c. replaces electrons lost by Photosystem II / PSII / P680 / chlorophyll a ✔ For mpc, do not accept just chlorophyll.

d. allows electrons «to continue» to pass along the electron transport chain ✔

e. provides protons/H+ «inside thylakoid» to help generate a «proton» gradient/maintain high concentration inside thylakoid ✔ For mpe, reject pumping of protons into the thylakoid as photolysis produces them inside the thylakoid.

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