DP Biology (first assessment 2025)

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Question 22M.2.SL.TZ2.7a

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Date May 2022 Marks available [Maximum mark: 5] Reference code 22M.2.SL.TZ2.7a
Level SL Paper 2 Time zone TZ2
Command term Outline Question number a Adapted from N/A
a.
[Maximum mark: 5]
22M.2.SL.TZ2.7a
(a)

Outline, using graphs, the effect of different factors that influence enzyme activity.

[5]

Markscheme
  1. enzymes have active sites that bind specific substrates;
  2. act as catalysts to speed up reactions
    OR
    lower activation energy;
  3. rate/activity increases with temperature;
  4. up to an optimum temperature;
  5. sharp decline in activity above (optimum temperature);
    (Graph has to be clearly asymmetrical for mpe)
    (Graph shown would earn mpc, mpd and mpe)
    ;
  6. rate/activity declines at a pH above and below the optimum pH
    (Graph shown would earn mpf)
    ;
  7. rate/activity increases sharply as substrate concentration goes up;
  8. above a certain concentration, the rate reaches a maximum/plateau;
    (Graph shown would earn mpg and mph)
    ; 
  9. competitive inhibitor present, as substrate concentration increases, enzyme requires higher concentration to achieve maximum rate / graph showing this with and without inhibitor;
  10. non-competitive inhibitor present, as substrate concentration rises, enzyme activity is lower at all substrate concentrations / graph showing shape with and without inhibitor;

Award [3 max] if there are no graphs.

For each graph, axes must be correctly labelled, the shape must be correctly drawn.

Marks can be awarded to a correctly annotated graph.

Examiners report

This question was the most popular choice of essay as well as the most successful.

Many earned full marks, but many others contained errors. Some of these errors included inverted axes, no abrupt curve drop for high temperatures, an asymmetric graph shown for pH, the optimum temperature or pH not mentioned or labelled.

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