A laboratory device transfers oxygen across a membrane into a liquid. The relative diffusion value is calculated using:
relative diffusion value = (surface area × concentration difference) ÷ membrane thickness
| Membrane | Surface area (cm²) | Concentration difference (mmol dm⁻³) | Thickness (mm) |
|---|---|---|---|
| A | 20 | 1.5 | 0.20 |
| B | 30 | 2.0 | 0.30 |
Calculate how many times greater the relative diffusion value for membrane B is than for membrane A.
Calculate the thickness membrane B would need to have for its relative diffusion value to equal that of membrane A, with all its other measurements unchanged.
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.