DP Biology (first assessment 2025)

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Question 21M.2.HL.TZ2.a

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Date May 2021 Marks available [Maximum mark: 7] Reference code 21M.2.HL.TZ2.a
Level HL Paper 2 Time zone TZ2
Command term Explain Question number a Adapted from N/A
a.
[Maximum mark: 7]
21M.2.HL.TZ2.a

Explain the role of hydrogen ions used in photosynthesis.

[7]

Markscheme

a. hydrogen ions (and oxygen) are obtained from photolysis of water ✔

b. (excited) electrons (from Photosystem II) contribute to generate a hydrogen ion/proton gradient
OR
protons build up in the thylakoid space/inside the thylakoid ✔

c. ATP synthase generates ATP by chemiosmosis/using the proton gradient/by movement of protons from the thylakoid space to the stroma ✔

d. (two) high energy/excited electrons (from Photosystem II) are passed through an electron transport chain ✔

e. NADP accepts H+ (from the stroma) / electrons to produce NADPH+/reduced NADP ✔

f. ATP/reduced NADP/NADPH+ are used by light-independent reactions/Calvin cycle in the stroma ✔

g. (in Calvin cycle) carbon fixation to ribulose bisphosphate/RuBP produces G3P ✔

h. ATP is used to transform G3P to TP ✔

i. reduced NADP/NADPH+ is used to transform G3P to TP ✔

Accept answers in an annotated diagram.

Accept NADPH2/NADPH/NADPH + H+ in place of NADPH+.

Examiners report

Question 6 was a popular question.

A relatively high scoring section, though many students failed to discuss the role of hydrogen in the light independent reactions.

Syllabus sections