Factors affecting the rate of diffusionSpec 8.4B
Three factors affect how fast particles diffuse across an exchange surface.
| Factor | Effect on rate of diffusion | Example in the body |
|---|---|---|
| Surface area | Larger surface area means a faster rate, because more particles can cross at once | Millions of alveoli in the lungs |
| Concentration gradient | A steeper gradient (bigger difference in concentration) means a faster rate | Blood flow and breathing keep the oxygen concentration lower in the blood than in the alveoli |
| Diffusion distance (thickness of the membrane) | A shorter distance means a faster rate | Alveolus and capillary walls are one cell thick |
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. The bigger the difference, the faster the net movement.