DP Biology (first assessment 2025)

Question 20N.1A.HL.TZ0.31

Date	November 2020	Marks available	[Maximum mark: 1]	Reference code	20N.1A.HL.TZ0.31
Level	HL	Paper	1A	Time zone	TZ0
Command term		Question number	31	Adapted from	N/A

31.

[Maximum mark: 1]

20N.1A.HL.TZ0.31

Two reactions of the Krebs cycle are shown.

What type of reactions are isocitrate and oxalosuccinate undergoing?

[1]

Markscheme

Examiners report

Nearly all candidates knew that one type of reaction was decarboxylation and, from the answers offered, the other had to be either oxidation or reduction. More candidates than expected got this wrong and thought that removal of hydrogen from a Krebs cycle intermediate is reduction.

Syllabus sections

C. Interaction and interdependence » C1.2. Cell respiration » C1.2.12. Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced NAD

Question 20N.1A.HL.TZ0.31

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