Catalase is an enzyme found in living tissues that catalyses the breakdown of hydrogen peroxide (H2O2\text{H}_2\text{O}_2H2O2) into water and oxygen gas.
An investigation was carried out to determine the effect of substrate concentration on the rate of catalase activity. Hydrogen peroxide solutions of different concentrations were prepared in separate boiling tubes. A fixed volume of catalase solution was added to each tube, and the volume of oxygen gas produced after 3 minutes3\text{ minutes}3 minutes was measured using a gas syringe.
The results of this investigation are shown in the table below:
| Concentration of hydrogen peroxide (%) | Volume of oxygen gas produced after 3 minutes3\text{ minutes}3 minutes (cm3\text{cm}^3cm3) |
|---|---|
| 0.5 | 12.0 |
| 1.0 | 22.5 |
| 1.5 | 31.0 |
| 2.0 | 38.0 |
| 2.5 | 40.5 |
Which of the following pairs of variables must be kept constant in this investigation?
the concentration of catalase and the volume of oxygen gas produced
the temperature of the reaction mixture and the concentration of catalase
the concentration of hydrogen peroxide and the pH of the buffer
the volume of oxygen gas produced and the concentration of hydrogen peroxide
