Molecular diffusion is the process by which molecules spread from areas of high concentration to areas of low concentration. This movement occurs due to the random motion of molecules, driven by thermal energy. As molecules collide and move, they gradually distribute themselves evenly in a given space. This phenomenon is essential in various natural processes, such as gas exchange in the lungs and the mixing of substances in solutions. Molecular diffusion plays a crucial role in biological systems, influencing how nutrients and waste products are transported within cells and across membranes.