What does diffusion involve?

Diffusion involves the movement of molecules from an area of high concentration to an area of low concentration. This process is driven by the concentration gradient, which is the difference in the concentration of a substance across a space. Molecules will naturally move to areas where they are less concentrated in an effort to reach equilibrium.

This means that diffusion is a passive process, occurring without the need for energy input. It plays a crucial role in many biological processes, such as the exchange of gases in the lungs, the movement of nutrients into cells, and the elimination of waste products. The correct choice highlights the fundamental concept that diffusion relies on the natural tendency of substances to spread out evenly in their environment.