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 its surface area, allowing more contact with the trypsin. This enhances the efficiency of the enzyme in breaking down the proteins, leading to quicker digestion.

The temperature at which the reaction occurs could be controlled.

The temperature can be kept constant by using a water bath to maintain the desired pH level during the experiment.

As the pH increases from 1 to 4, the time taken for the food to digest decreases significantly. The shortest time for digestion occurs at pH 4, while the time taken increases again beyond pH 4, indicating that pH affects the enzyme's activity optimally at pH 4.

To calculate the rate of digestion, we can use the formula:

Rate of digestion =

rac{mass ext{ digested}}{time ext{ taken}}

At pH 4: 1.5 g digested at 0.8 g/min implies that it took:
rac{1.5 g}{0.8 g/min} = 1.875 mins

At pH 1, with the recorded time of 42 minutes, the rate of digestion is:
rac{1.5 g}{42 min} = 0.0357 g/min

Rounded to one significant figure is 0.04 g/min.

The difference in the rate of reaction is attributed to the optimal pH for trypsin activity. At pH 4, trypsin functions most efficiently, leading to faster digestion, while at pH 1, the enzyme may be denatured or less active, resulting in a slower reaction.