The concentration gradient refers to the gradual change in the concentration of solutes present in a solution between two regions. In biology, a gradient results from an unequal distribution of ions across the cell membrane. When this happens, solutes move along a concentration gradient. This kind of movement is called diffusion. Diffusion refers to the net movement of molecules from higher to lower concentration, and may be classified as simple or facilitated. A simple diffusion would not need a carrier molecule to occur, unlike facilitated diffusion. Both simple and facilitated diffusion processes occur when there is a concentration gradient. The movement of molecules continues as long as there is a concentration gradient. Equilibrium is attained when there is no longer a net movement of molecules between two areas.
The movement of solutes along a concentration gradient is common in many biological processes. For a more elaborated discussion, read the Tutorial in Cell Biology where various ways substances pass through a cell membrane are described.
- density gradient