Answer:
the pH
Explanation:
The condition that should not be kept the same in each of the five test tubes is the pH.
Since the aim of the experiment is to investigate the effect of pH on the activity of the lipase enzyme, the pH is, therefore, the independent variable. Thus, it must be controlled or varied in all the test tubes in order to see its effect on the activity of the enzyme, which, in this case, would be the dependent variable.
