Some students investigate the rate of anaerobic fermentation of yeast. They prepare fermentation flasks containing yeast and glucose solutions of varying concentrations, plugging each flask with a cotton wool plug.
Why do the students plug the flasks with cotton wool rather than sealing them completely with rubber bungs? Select one option:
The students want to see if the concentration of the glucose solution affects the rate of fermentation.
The table shows their results:
| Glucose concentration (%) | Mass at the start (g) | Mass after 8 days (g) |
|---|---|---|
| 2 | 250.0 | 244.2 |
| 5 | 250.0 | 238.1 |
| 10 | 250.0 | 231.4 |
| 15 | 250.0 | 229.1 |
Calculate the loss in mass per day of the flask and contents with a 10% glucose concentration. Give your answer to 3 significant figures.
Describe the effect of the glucose concentration on the rate of fermentation of the yeast.
The students made sure that all yeast and glucose mixtures had a mass of 250.0 g250.0\text{ g}250.0 g at the start of the experiment. Explain why this helps the students to analyse the results.
What is the independent variable in the students' investigation?
During the experiment, water vapour evaporates and escapes through the cotton wool plug along with the carbon dioxide gas. Explain why this can produce inaccurate results and how they can change their method to correct this.
44 exam-style questions on OCR GCSE Biology Practical skills. Each one has a worked solution and a mark scheme showing where the marks go.