A student uses a model to compare diffusion through two artificial exchange surfaces. The model uses the following expression.
relative diffusion value=surface area×concentration differencemembrane thickness \text{relative diffusion value}=\frac{\text{surface area}\times\text{concentration difference}}{\text{membrane thickness}} relative diffusion value=membrane thicknesssurface area×concentration differenceThe measurements are shown in the table.
| Exchange surface | Surface area | Concentrations on the two sides | Membrane thickness |
|---|---|---|---|
| A | 12 mm2 | 10 and 4 mmol dm−34\,\mathrm{mmol\,dm^{-3}}4mmoldm−3 | 0.30 mm |
| B | 18 mm2 | 12 and 3 mmol dm−33\,\mathrm{mmol\,dm^{-3}}3mmoldm−3 | 0.20 mm |
Calculate the fold change in relative diffusion value from exchange surface A to exchange surface B.
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.