Two regions of a fish gill have exchange surfaces with the same area and thickness. The temperature is constant. The initial dissolved oxygen concentrations are shown in the table.
| Gill region | Oxygen concentration in water in mmol dm−3\mathrm{mmol\,dm^{-3}}mmoldm−3 | Oxygen concentration in blood in mmol dm−3\mathrm{mmol\,dm^{-3}}mmoldm−3 |
|---|---|---|
| G | 0.30 | 0.10 |
| H | 0.24 | 0.04 |
Which statement about the initial net rate of oxygen diffusion from the water into the blood at regions G and H is correct?
H has the higher initial net rate because its water concentration is six times its blood concentration.
Both regions have zero initial net diffusion because oxygen particles cross each exchange surface in both directions.
The initial net rates are equal because the oxygen concentration difference is 0.20 mmol dm−30.20\,\mathrm{mmol\,dm^{-3}}0.20mmoldm−3 at both regions.
G has the higher initial net rate because its water and blood concentrations add to 0.40 mmol dm−30.40\,\mathrm{mmol\,dm^{-3}}0.40mmoldm−3.
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.