What is an example of concentration gradient?

An example of concentration gradient is food dye diffusing in a glass of water. A concentration gradient is the change in concentration in a solution measured over the distance.

In the example, the concentration on the dye is found stronger where the dye is more vibrant. The solution that is more diluted is clear without traces of the dye. The dye diffuses until the water is a uniform color throughout the sample. Concentration gradients are especially important when looking at the diffusion at the cell membrane level. Diffusion can be passive or active. In passive diffusion, the ions are able to move freely across the membrane. In active diffusion, the ions move to lower areas of concentration.