Edexcel IGCSE Biology 2.13 pH and enzyme function

Practise pH and enzyme function by explaining optimum pH, active-site changes and denaturation in fruit or gelatine data.

Exam points

Explain graph or table trends by linking time or volume changes to optimum pH.
Link acidic or alkaline conditions to denaturation and altered active-site shape.
Apply active-site reasoning to fruit browning, gelatine digestion or urease contexts.

[Maximum number: 3]

Pineapple juice contains a protease called bromelain.
A student uses this method to investigate the digestion of solid gelatine protein by bromelain.
- place solid gelatine protein into a test tube up to a height of 5 cm
- mix $5 \mathrm{~cm}^{3}$ pineapple juice with $1 \mathrm{~cm}^{3}$ of pH 4 buffer
- place $1 \mathrm{~cm}^{3}$ of the pineapple juice and buffer solution on top of the gelatine
- leave for one hour in a water bath set to $37^{\circ} \mathrm{C}$
- measure the height of the solid gelatine and use it to calculate the volume of gelatine that has been digested

Repeat the method three more times.
The diagram shows part of the student's method.

Figure for Question 2.13 pH and enzyme function question 1 — Edexcel IGCSE Biology

The student repeats the investigation with different pH buffers.

The table shows their results.

Table for Question 2.13 pH and enzyme function question 1 — Edexcel IGCSE Biology

Explain the effect of changing the pH on the mean volume of gelatine digested.

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2.13 pH and enzyme function question 1