Improving Enzyme Activity Experiment Reliability

A research study aimed to explore the influence of different concentrations of a chemical solution on the rate of enzyme activity. The researchers prepared three groups of samples, each with a different concentration of the solution: low, medium, and high. They then measured the rate of reaction by observing the amount of product formed over a fixed period.

The researchers recorded their findings, detailing how the reaction rate varied with the concentration of the enzyme solution. Data showed that the high concentration group exhibited the fastest reaction rate, followed by the medium concentration group, with the low concentration group demonstrating the slowest rate. This experiment was aimed at determining the optimal concentration for enzyme activity.

Based on this experiment's design, which of the following alterations would most likely improve the experiment's reliability in assessing the effect of concentration on enzyme activity?