A researcher places a membrane-coated fertiliser pellet in water inside a closed container. Mineral ions diffuse through the membrane into the water. The membrane surface area, membrane thickness and temperature remain constant.
The table shows the total amount of mineral ions in the water. It also shows the mean concentration difference across the membrane during each time interval.
| Time in minutes | Total amount of mineral ions in the water in mg\mathrm{mg}mg | Mean concentration difference during the interval ending at this time in g dm−3\mathrm{g\,dm^{-3}}gdm−3 |
|---|---|---|
| 0 | 0 | — |
| 2 | 14 | 7.0 |
| 5 | 29 | 5.0 |
| 9 | 41 | 3.0 |
Calculate the percentage decrease from the fastest mean rate of diffusion to the slowest mean rate of diffusion.
Explain the pattern in the mean rate of diffusion using the mean concentration difference data.
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.