A researcher uses artificial barriers to model the exchange of oxygen through capillary walls. Each barrier has the same surface area and the same oxygen concentration difference across it.
| Model | Number of layers in the barrier | Rate of oxygen transfer in micrograms per minute |
|---|---|---|
| P | 1 | 8.0 |
| Q | 2 | 4.0 |
| R | 4 | 2.0 |
| S | 8 | not measured |
Explain which model, P, Q or R, best represents the exchange surface of a capillary.
Calculate the predicted rate of oxygen transfer through model S.
67 exam-style questions on Edexcel GCSE Biology 8.2 Blood and circulation, covering 8.2.1 Structure and function of the blood, 8.2.2 Structure of blood vessels, 8.2.3 Structure of the heart and circulatory system, and 8.2.4 Cardiac output. Each one has a worked solution and a mark scheme showing where the marks go.