HSA 2007 Biology Item 22print
Use the information and the graph below to answer the following question.
Catalase is an enzyme found in plant and animal cells. Hydrogen peroxide is a harmful substance found in cells. Catalase causes hydrogen peroxide to break down into water and oxygen.
A student conducted an experiment to determine whether plant and animal cells have the same amount of catalase. She used liver and potato tissues in the experiment. The student followed the procedures below.
The graph below shows the results from the experiment.

Which of these factors was not controlled in the experiment?
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