Edexcel IGCSEBiologyGeneral Applications6 Marks
The graph shows the effect of pH on the activity of two enzymes, P and Q. [Figure 4]
- (a)Determine the optimum pH for enzyme P and enzyme Q.[2]
- (b)Explain why enzyme Q would be inactive in the stomach.[2]
- (c)Suggest why maintaining a constant body temperature is important for enzyme activity in humans.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme. The mark or mark type is shown in brackets.
- (a) B1 for P = pH 2; B1 for Q = pH 8; (2 marks)
- (b) M1 for stomach pH is very low / acidic (approx. pH 1-3); A1 for enzyme Q optimum pH is 8 / denatures at low pH / active site changes shape; (2 marks)
- (c) M1 for enzymes have an optimum temperature (e.g. 37 °C); A1 for (if temperature is too high) enzymes denature / active site changes shape / (if too low) reduced kinetic energy / reduced collisions; (2 marks)
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