DP Chemistry (last assessment 2024)

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Question 20N.3.hl.TZ0.10b(ii)

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Date November 2020 Marks available [Maximum mark: 1] Reference code 20N.3.hl.TZ0.10b(ii)
Level hl Paper 3 Time zone TZ0
Command term Outline Question number b(ii) Adapted from N/A
b(ii).
[Maximum mark: 1]
20N.3.hl.TZ0.10b(ii)

The kinetics of an enzyme-catalysed reaction are studied in the absence and presence of an inhibitor. The graph represents the initial rate as a function of substrate concentration.


(b(ii))

Outline the significance of the value of the Michaelis constant, Km.

[1]

Markscheme

Km is an inverse measure of affinity of substrate for enzyme
OR
higher Km indicates higher substrate concentration is needed for enzyme saturation
OR
low value of Km means reaction is fast at low substrate concentration ✔


Idea of “inverse relationship” must be conveyed.

Examiners report

The stronger candidates scored all three marks here for the four correct values. Most scored at least one mark for the Vmax values in the absence and presence of the inhibitor. The Km values sometimes were outside the permitted ±0.1 range.

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