DP Biology (first assessment 2025)

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Question 22N.2.HL.TZ0.b

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Date November 2022 Marks available [Maximum mark: 5] Reference code 22N.2.HL.TZ0.b
Level HL Paper 2 Time zone TZ0
Command term Describe Question number b Adapted from N/A
b.
[Maximum mark: 5]
22N.2.HL.TZ0.b

Describe how ATP is produced by Photosystem II in the light-dependent stage of photosynthesis.

[5]

Markscheme
  1. light (energy) absorbed by pigments/chlorophyll/photosystems;
  2. excited electrons passed to electron carriers/electron transport chain;
  3. protons/hydrogen ions pumped into thylakoid (space);
  4. proton gradient/high proton concentration generated;
  5. protons pass via ATP synthase to the stroma;
  6. ATP synthase phosphorylates ADP/ATP synthase converts ADP to ATP;
  7. photophosphorylation/chemiosmosis;
  8. ATP synthase/electron carriers/proton pumps/photosystems/pigment are in the thylakoid membrane;
Examiners report

There was evidence that many candidates had prepared carefully for this topic and were fully familiar with the sequence of events in the light-dependent reactions that result in ATP production. In some of the weaker answers the protons were moving in the wrong direction and some candidates were confused about the differences in structure between chloroplasts and mitochondria and therefore the nature of the proton gradient.

Syllabus sections