DP Biology (first assessment 2025)

Test builder »

Question 22M.2.HL.TZ1.7c

Select a Test
Date May 2022 Marks available [Maximum mark: 7] Reference code 22M.2.HL.TZ1.7c
Level HL Paper 2 Time zone TZ1
Command term Explain Question number c Adapted from N/A
c.
[Maximum mark: 7]
22M.2.HL.TZ1.7c
(c)

Explain the role of the electron transport chain in the generation of ATP by cell respiration.

[7]

Markscheme
  1. electron transport chain performs chemiosmosis / chemiosmosis generates ATP;
  2. receives energy/electrons from oxidation reactions/from Krebs cycle/glycolysis;
  3. receives electrons from reduced NAD/NADH/reduced FAD/FADH;
  4. energy released as electrons pass from carrier to carrier (in the chain);
  5. release of energy (from electron flow) coupled to proton pumping;
  6. protons pumped into intermembrane space;
  7. creates proton gradient;
  8. protons diffuse back/move down the concentration gradient (across membrane);
  9. protons pass through ATP synthase;
  10. protons return to the matrix;
  11. flow of protons provides energy for generating ATP;
  12. electrons transferred to oxygen at end of electron transport chain;
Examiners report

For well-prepared candidates this question posed no difficulty and there were some excellent detailed accounts of chemiosmosis. The discrimination index was the highest for any question on the paper, indicating that there was no room for lucky guesses about the biology here!

Syllabus sections