A student investigated the effect of pH on the rate of protein breakdown by the digestive enzyme pepsin, which is found in the stomach.
The student mixed equal volumes of a cloudy egg white (protein) suspension with a pepsin solution in test tubes maintained at a constant temperature of 37∘C37^\circ\text{C}37∘C using different buffer solutions. The time taken for each suspension to turn completely clear (indicating complete breakdown of the protein) was recorded.
Our results are shown in the table below:
| pH of solution | Time taken for the suspension to turn clear (minutes) |
|---|---|
| 1.5 | 3 |
| 3.0 | 8 |
| 7.0 | Suspension remained cloudy after 20 minutes |
| 9.0 | Suspension remained cloudy after 20 minutes |
Explain why the protein was not broken down in the test tube at pH 7.0.
44 exam-style questions on AQA GCSE Biology 2.2 Animal tissues, organs and organ systems, covering 2.2.1 The human digestive system, 2.2.2 The heart and blood vessels, 2.2.3 Blood, 2.2.4 Coronary heart disease: a non-communicable disease, 2.2.5 Health issues, 2.2.6 The effect of lifestyle on some non-communicable diseases, and 2.2.7 Cancer. Each one has a worked solution and a mark scheme showing where the marks go.