Movement of Materials in CellsCells are bathed in a watery matrix and conduct most of their reactions in a similar watery fluid—a solution in which water is the solvent and the numerous molecules and ions dissolved in it are the solutes. The solutes include protons (H+), ions like sodium (Na+), potassium (K+), calcium (Ca2+), organic molecules such as sucrose (C12H22O11), polar and nonpolar molecules, and a host of other substances, the chemical nature of which determines the ease or difficulty with which they move across membranes. DiffusionAll molecules possess kinetic energy and move in a random fashion. In solutions, solutes become distributed uniformly as they diffuse and occupy all available space. Diffusion is the net movement of a substance from a region of its higher concentration to a region of its lower as a result of the
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concentration gradient, free water molecules