Question

questions 15 and 16 refer to the following.
figure 1 rate of an enzyme - catalyzed reaction
researchers investigated the dynamics of a reaction catalyzed by an enzyme. the researchers prepared a series of reactions, each with the same concentration of enzyme but with different concentrations of substrate. the researchers measured the amount of product in each reaction mixture after 5 minutes. the results are shown in figure 1.

1. mark for review

which of the following experimental designs would best allow researchers to investigate the effect of ph on the rate of the enzyme - catalyzed reaction?
a measure reaction rates at different ph levels when the enzyme concentration remains the same and the substrate concentration is 100 μm.
b measure the ph of the reaction mixture when the enzyme concentration remains the same and substrate concentrations vary between 0 μm and 1,000 μm.
c measure reaction rates when the enzyme concentration remains the same but the ph of the reaction mixture increases and the substrate concentration increases from 0 μm to 1,000 μm.
d measure reaction rates when the substrate concentration is 100 μm and both the ph of the reaction mixture and the enzyme concentration are increased.

Explanation:

To investigate the effect of pH on the rate of an enzyme - catalyzed reaction, the independent variable should be pH. In experimental design, when studying the effect of one variable (here pH), other variables (such as substrate concentration and enzyme concentration) should be kept constant.

• Option A: Measures reaction rates at different pH levels while keeping enzyme concentration and substrate concentration (100 μM) the same. This design isolates pH as the variable affecting the reaction rate.
• Option B: Studies the effect of substrate concentration, not pH.
• Option C: Studies the effect of enzyme concentration, not pH.
• Option D: Changes multiple variables (pH, substrate concentration, enzyme concentration), so it cannot isolate the effect of pH.

Answer:

A. Measure reaction rates at different pH levels when the enzyme concentration remains the same and the substrate concentration is 100 μM.