Water Movement (3)

The molecules in a solution are not static, they are in continuous motion. Diffusion results in the net movement of molecules from regions of high concentration to regions of low concentration. This tendency for a system to evolve toward and even distribution of molecules can be understood as a consequence of the second law of thermodynamics, which tells us that spontaneous processes evolve in the direction of increasing entropy or disorder. Diffusion represents the natural tendency of systems to move toward the lowest possible energy state. Fick’s first law describes the process of diffusion, which is most effective over short distances. Diffusion in solutions can be effective within cellular dimensions but is far too slow to be effective over long distances. The average time required for a glucose molecule to diffuse across a cell with a diameter of 50 µm is 2.5 s. However, the average time needed for the same glucose molecule to diffuse a distance of 1 m in water is approximately 32 years.