Fick's law shows how three factors affect the rate of diffusion.
rate of diffusion∝surface area×concentration differencethickness of membrane \text{rate of diffusion} \propto \frac{\text{surface area} \times \text{concentration difference}}{\text{thickness of membrane}} rate of diffusion∝thickness of membranesurface area×concentration differenceIn a patient with a lung disease, the total surface area of the alveoli has fallen to 60% of the normal value. The thickness of the membrane between the air and the blood has increased from 0.5 μm0.5\ \mu\text{m}0.5 μm to 1.5 μm1.5\ \mu\text{m}1.5 μm.
Calculate the rate of oxygen diffusion in the patient as a percentage of the normal rate.
Assume that the concentration difference has not changed.
The patient is given air with a higher concentration of oxygen to breathe.
Explain how this helps the patient.
Calculate how many times greater the concentration difference must be to return the rate of oxygen diffusion to normal.
42 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.