A model is used to compare diffusion of dissolved particles across a plant root exchange surface. The temperature and membrane material remain unchanged.
| Condition | Concentration on one side (mmol dm⁻³) | Concentration on the other side (mmol dm⁻³) | Surface area (mm²) | Membrane thickness (mm) |
|---|---|---|---|---|
| Before | 9 | 3 | 40 | 0.20 |
| After | 12 | 2 | 60 | 0.30 |
Calculate how many times greater the net diffusion rate is after the change than before the change. Give your answer to 2 significant figures.
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.