AP BIOLOGY

Detailed explanation-1: -Since diffusion moves materials from an area of higher concentration to the lower, it is described as moving solutes “down the concentration gradient". The end result is an equal concentration, or equilibrium, of molecules on both sides of the membrane. At equilibrium, movement of molecules does not stop.

Detailed explanation-2: -During diffusion, when the concentration of molecules on both sides of a membrane is the same, the molecules will continue to move across the membrane in both directions.

Detailed explanation-3: -When the concentration of a solute is equal on both sides of a membrane, the two solutions (inside and outside the membrane) are said to be isotonic. This does not mean that there is no movement through the membrane, however, just that the movement is such that the concentrations stay the same.

Detailed explanation-4: -Diffusion across a membrane Eventually, the concentration of the molecules on each side of the cell membrane will be the same and particles will be going back and forth through the membrane at the same rate. At that point, equilibrium is reached.