A researcher investigates the transfer of carbon dioxide from a fixed mass of respiring muscle tissue into nearby capillary blood.
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 differenceThe researcher obtains these measurements.
| Measurement | Healthy tissue | Injured tissue |
|---|---|---|
| total area available for exchange in mm2\mathrm{mm^2}mm2 | 140 | 98 |
| mean thickness of the exchange barrier in μm\mu\mathrm{m}μm | 4.0 | 7.0 |
The same carbon dioxide concentration difference was maintained when each set of measurements was obtained.
Use the measurements to calculate the diffusion rate in the injured tissue, expressed as a percentage of the rate in the healthy tissue.
The rate of blood flow through the capillaries in the injured tissue is increased.
Explain why this can increase the transfer of carbon dioxide out of the muscle cells.
A proposed treatment is intended to restore the healthy-tissue diffusion rate without altering the area or barrier thickness of the injured tissue.
Calculate the factor by which the carbon dioxide concentration difference would need to be multiplied.
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.