A researcher investigated the diffusion of urea across a thin, partially permeable membrane. The same membrane area and temperature were used in each test. The table shows the urea concentrations at the start of each test and the initial rate of diffusion from solution X to solution Y.
| Test | Urea concentration in solution X in mmol per dm³ | Urea concentration in solution Y in mmol per dm³ | Initial rate of diffusion in micromol per cm² per minute |
|---|---|---|---|
| 1 | 8 | 6 | 0.30 |
| 2 | 10 | 6 | 0.60 |
| 3 | 14 | 6 | 1.20 |
Calculate the expected initial rate of diffusion when the urea concentration in solution X is 18 mmol per dm³ and the urea concentration in solution Y is 6 mmol per dm³.
Explain why the rate of diffusion would decrease if the test continued for a long time.
140 exam-style questions on AQA GCSE Biology 1.3 Transport in cells, covering 1.3.1 Diffusion, 1.3.2 Osmosis, and 1.3.3 Active transport. Each one has a worked solution and a mark scheme showing where the marks go.