Question 21N.2.HL.TZ0.8c
| Date | November 2021 | Marks available | [Maximum mark: 4] | Reference code | 21N.2.HL.TZ0.8c |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Distinguish | Question number | c | Adapted from | N/A |
Distinguish between competitive and non-competitive enzyme inhibition.
[4]
Accept mpd in a graph.
Accept mpa, mpb or mpc on an annotated diagram.
[Source: Enzyme inhibition curves,
ImranKhan1992, Available at: https://
commons.wikimedia.org/wiki/
File:Enzyme_kinetics_curve.png#/media/
File:Enzyme_kinetics_curve.png CC0 1.0
Universal (CC0 1.0) Public Domain Dedication
https://creativecommons.org/publicdomain/
zero/1.0/deed.en Source adapted.]
In a parallel way to 6(c) and 7(b), there was a tendency for candidates to write about the two types of enzyme inhibition separately and as a result not to distinguish between them fully. For example. many candidates stated that competitive inhibitors show some chemical similarity to the substrate but did not then state that non-competitive inhibitors are typically dissimilar. An error which is repeatedly seen in enzyme questions is for candidates to state that the active site is on the substrate rather than the enzyme. Some candidates drew sketch graphs to show the difference between competitive and non-competitive inhibitors in the effect of substrate concentration, but either did not label the x-axis or labelled it ‘time’ rather than ‘substrate concentration’.
