The diagram shows the effect of changing the temperature on the time taken for an enzyme to digest starch.
Which statement about the results is correct?
A) The optimum temperature is at X and the rate of reaction decreases between X and Y.
B) The optimum temperature is at X and the rate of reaction increases between X and Y.
C) The optimum temperature is at Y and the rate of reaction decreases between X and Y.
D) The optimum temperature is at Y and the rate of reaction increases between X and Y.
▶️ Answer/Explanation
Ans: D
The graph shows that the time taken for starch digestion decreases as temperature increases from X to Y, indicating the rate of reaction increases in this range. The optimum temperature is where the reaction is fastest (lowest time), which occurs at Y.
Option A and B incorrectly state X as the optimum, while C wrongly claims the rate decreases. Since the rate increases and Y is the optimum, the correct answer is D.
The graph shows the effect of pH on the rate of an enzyme-catalysed reaction.
What explains the effect of pH on the reaction rate?
A) As the pH increases from 5 to 7, the kinetic energy increases.
B) As the pH increases from 7 to 9, the frequency of enzyme and substrate collisions increases.
C) The shape of the enzyme’s active site changes as the pH increases from 7 to 9.
D) The substrate denatures at pH7.
▶️ Answer/Explanation
Ans: C
The graph shows that the reaction rate decreases as pH moves away from the optimum (around pH 7). This is because changes in pH alter the enzyme’s active site shape (C), reducing its ability to bind with the substrate.
Kinetic energy (A) is temperature-dependent, not pH. Collision frequency (B) is unrelated to pH changes. Substrates (D) do not denature; only enzymes do. Thus, the correct explanation is C.