How does concentration gradient affect the rate of diffusion?

Diffusion is the movement of a substance from areas of high concentration to areas of low concentration, down a concentration gradient. As a result of diffusion, substances may move in and out of cells, across the cell membrane. The substance moves from a highly concentrated area to a lowly concentrated area. For instance, oxygen diffuses from alveoli to the blood because there is a lower concentration of oxygen in the blood than in the alveoli. The greater the concentration gradient, the greater the rate of diffusion.