A student investigated the effect of temperature on the rate of lipid hydrolysis by the enzyme lipase. This metabolic reaction produces fatty acids, which decrease the pH of the reaction mixture.
The student used the following method:
Table 1 shows the student's results at 20 ∘C20\text{ }^{\circ}\text{C}20 ∘C:
| Time (minutes) | 0 | 10 | 20 | 30 | 40 | 50 |
|---|---|---|---|---|---|---|
| pH | 8.5 | 8.0 | 7.1 | 6.2 | 5.6 | 5.5 |
How could the student keep the reaction mixture at a constant temperature for the duration of the 50-minute experiment?
Identify one variable, other than temperature, that the student should keep constant.
Use the data in Table 1 to calculate the mean rate of decrease in pH per minute between 10 minutes10\text{ minutes}10 minutes and 40 minutes40\text{ minutes}40 minutes. Show your working.
If the experiment is repeated at 30 ∘C30\text{ }^{\circ}\text{C}30 ∘C (which is below the lipase's denaturation temperature), describe two expected features of the pH curve compared to the 20 ∘C20\text{ }^{\circ}\text{C}20 ∘C curve.