A scientist is developing a membrane cartridge to remove urea from blood. Urea diffuses from the blood, across the membrane, into a collecting solution.
The scientist compares two cartridges. The membrane material and temperature are the same in both cartridges.
| Cartridge | Membrane surface area in cm2\mathrm{cm^2}cm2 | Urea concentration in blood in mmol dm−3\mathrm{mmol\,dm^{-3}}mmoldm−3 | Urea concentration in collecting solution in mmol dm−3\mathrm{mmol\,dm^{-3}}mmoldm−3 | Membrane thickness in mm\mathrm{mm}mm | Rate of diffusion in μmol min−1\mathrm{\mu mol\,min^{-1}}μmolmin−1 |
|---|---|---|---|---|---|
| A | 60 | 5.0 | 1.0 | 0.20 | 12 |
| B | 90 | 4.0 | 2.0 | 0.10 | to be calculated |
Calculate the rate of diffusion of urea through cartridge B.
Show your working.
The scientist claims that increasing the surface area of cartridge B from 90 cm2 to 120 cm2 would increase the rate of diffusion more than reducing the membrane thickness from 0.10 mm to 0.075 mm.
In each case, all other factors would remain unchanged.
Explain whether the scientist's claim is supported.
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.