Scientists investigated the effect of pH on the survival of bacteria.
They added 100 000 100\,000\,100000 bacteria to each of five solutions with different pH values. The solutions were kept at 37 ∘C37\,^{\circ}\text{C}37∘C.
After 1 hour, they counted the number of bacteria that survived.
The Table shows the results.
Table
| pH of solution | Number of bacteria that survived |
|---|---|
| 1 | 200 |
| 2 | 1 500 |
| 3 | 12 000 |
| 5 | 60 000 |
| 7 | 95 000 |
Calculate the percentage of bacteria that were killed at pH 2.
The pH inside the stomach is about 2.
Use the Table to explain how the stomach protects the body from pathogens in food.
Some people take medicines that raise the pH in the stomach to about pH 5.
Explain why these people may be more likely to get infections of the gut.
Give one reason why the solutions were kept at 37 ∘C37\,^{\circ}\text{C}37∘C.
45 exam-style questions on Edexcel GCSE Biology 5.2 Plant and body defences, covering 5.2.1 Physical plant defences, 5.2.2 Chemical plant defences, 5.2.3 Detecting plant diseases, and 5.2.4 Human physical and chemical defences. Each one has a worked solution and a mark scheme showing where the marks go.