There are often several different types of molecules in a solution. The motion of each type of molecule is random and independent of other molecules in the solution. Each molecule moves down its own concentration gradient, from a region of its high concentration to a region of its low concentration.

Though the net movement of molecules is down their concentration gradient, at any time molecules can move in both directions as long as the membrane is permeable to the molecule. Keep this in mind while you take a closer look at the beaker below.

Continue to Movement of Molecules in Cells.