A laboratory oxygen exchanger contains a thin membrane. Oxygen can diffuse across the membrane from liquid A into liquid B.
In arrangement P, the liquids flow in opposite directions. In arrangement Q, the liquids flow in the same direction.
The volume flow rate of each liquid is 1.0 dm³ per minute in both arrangements. The membrane area, membrane thickness and temperature are the same in both arrangements.
The table shows the oxygen concentrations at four positions along the membrane. Position is measured from the inlet of liquid A.
| Arrangement | Position along membrane in cm | Oxygen concentration in liquid A in mg dm⁻³ | Oxygen concentration in liquid B in mg dm⁻³ |
|---|---|---|---|
| P | 0 | 10.0 | 6.0 |
| P | 1 | 8.0 | 4.0 |
| P | 2 | 6.0 | 2.0 |
| P | 3 | 4.0 | 0.0 |
| Q | 0 | 10.0 | 0.0 |
| Q | 1 | 6.0 | 4.0 |
| Q | 2 | 5.5 | 4.5 |
| Q | 3 | 5.0 | 5.0 |
Explain which arrangement has the greater overall rate of oxygen transfer from liquid A into liquid B.
The flow speed of liquid A stays the same. Suggest how reducing the flow speed of liquid B in arrangement P would affect the overall rate of oxygen transfer.
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.