A researcher measures gas pressures in an alveolus and its surrounding capillary. The pressure of each gas is a measure of its concentration.
| location | oxygen pressure in kPa | carbon dioxide pressure in kPa |
|---|---|---|
| alveolar air | 13.3 | 5.3 |
| blood entering the capillary | 5.3 | 6.1 |
| blood leaving the capillary | 12.7 | 5.4 |
In a second mammal, the total thickness of the alveolar and capillary walls is twice as great. The alveolar oxygen pressure remains 13.3 kPa and the oxygen pressure in the blood entering the capillary remains 5.3 kPa. The surface area, ventilation and blood flow are unchanged. All other relevant conditions are unchanged apart from the total wall thickness.
Explain how the structure and functioning of the alveoli account for the data in the table and how the greater wall thickness would affect the oxygen pressure in the blood leaving the capillary of the second mammal.
102 exam-style questions on Edexcel GCSE Biology 8.1 Exchange surfaces and diffusion, covering 8.1.1 Introduction to exchange and transport, 8.1.2 Alveoli adapted for gas exchange, 8.1.3 Factors affecting rate of diffusion, and 8.1.4 Rate of diffusion using Fick's law. Each one has a worked solution and a mark scheme showing where the marks go.