5 (a) (i) Which food group is digested by trypsin? A carbohydrate B lipids C fibre D proteins (ii) The food is mashed before the trypsin is added - Edexcel - GCSE Biology - Question 5 - 2020 - Paper 1

Mashing the food increases the surface area available for trypsin to act upon. This allows for more efficient enzyme action, leading to faster digestion.

One variable that could be controlled is the temperature of the solutions used in the experiment.

The temperature can be controlled by using a water bath to maintain a constant temperature for all test tubes during the experiment.

The data shows that as the pH increases from 1 to 4, the time taken to digest the food decreases significantly, indicating that pH 4 is the optimum condition for digesting the food. However, beyond pH 4, particularly at pH 6, the time taken to digest the food increases, indicating that higher pH levels reduce enzyme activity.

To find the rate of digestion at pH 1, we use the formula:

$ext{Rate} = \frac{\text{mass of food}}{\text{time taken}}$

Substituting in the known values:

$\text{Rate} = \frac{1.5 g}{42 min} \approx 0.03571 g/min$

Thus, to one significant figure, the rate is 0.04 g/min.

At pH 1, the environment is highly acidic, which is not optimal for trypsin activity. As a result, the rate of reaction is slower than at pH 4. Trypsin's activity peaks at pH 4, where it is most effective, leading to a faster rate of reaction. Thus, the difference in reaction rates can be attributed to the enzyme’s optimum pH.