A manufacturer tests a dialysis membrane before it is used in a machine. The membrane allows urea to pass through. In each test, a solution representing blood is separated from a solution on the dialysis-fluid side.
The table shows the urea concentrations at the start of each test.
| Test | Urea concentration in the solution representing blood / mmol dm−3\mathrm{mmol\,dm^{-3}}mmoldm−3 | Urea concentration in the solution on the dialysis-fluid side / mmol dm−3\mathrm{mmol\,dm^{-3}}mmoldm−3 |
|---|---|---|
| 1 | 14 | 2 |
| 2 | 8 | 2 |
| 3 | 3 | 6 |
Calculate the ratio of the urea concentration difference across the membrane in test 1 to the urea concentration difference in test 2.
Give your answer in its simplest form.
Predict how the rate of urea movement across the membrane at the start of test 1 compares with the rate at the start of test 2.
Explain your prediction.
Predict the direction of the net movement of urea in test 3.
Explain your answer.
94 exam-style questions on Edexcel GCSE Biology 7.4 Blood glucose and the urinary system, covering 7.4.1 Insulin and blood glucose control, 7.4.2 Glucagon and blood glucose regulation, 7.4.3 Type 1 and type 2 diabetes, 7.4.4 Structure of the urinary system, 7.4.5 Structure and function of the nephron, 7.4.6 ADH and water regulation, 7.4.7 Treatments for kidney failure, and 7.4.8 Production of urea in the liver. Each one has a worked solution and a mark scheme showing where the marks go.