DP Biology (first assessment 2025)

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Question SPM.2.HL.TZ0.9c

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Date May Specimen-2023 Marks available [Maximum mark: 4] Reference code SPM.2.HL.TZ0.9c
Level HL Paper 2 Time zone TZ0
Command term Outline Question number c Adapted from N/A
c.
[Maximum mark: 4]
SPM.2.HL.TZ0.9c
(c)

Rotenone is a naturally occurring toxin that blocks the electron transport chain in insects and fish. Outline the consequences of exposure to a toxin like rotenone for cell respiration.

[4]

Markscheme
  1.  lower rate of aerobic respiration / inhibits aerobic respiration;
  2.  reduced NAD (not oxidised) accumulates;
  3.  fewer/no electrons (from reduced NAD and FADH) to be transported by carriers;
  4.  less/no energy to transfer protons (from matrix to intermembrane space);
  5.  proton gradient cannot be maintained;
  6.  less/no diffusion of protons through ATP synthase;
  7.  ADP is not phosphorylated / less ATP produced / no energy to produce ATP;
  8.  oxygen not binding to protons / accepting electrons / no water formed;

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