What process allows molecules to move from an area of higher concentration to an area of lower concentration?

The correct choice is diffusion because it describes the natural movement of molecules from a region where they are in higher concentration to a region where they are in lower concentration. This process occurs due to the random movement of molecules and is driven by the concentration gradient, which is the difference in concentration between two areas.

Diffusion is a fundamental concept in biology, as it explains how substances, such as gases or nutrients, move across cell membranes and are distributed throughout cells and organisms. This passive transport mechanism does not require energy, relying instead on the inherent kinetic energy of the molecules involved.

The other options refer to different biological processes or terms. Differentiation relates to the process by which cells become specialized in structure and function. Diastole refers to the phase of the cardiac cycle when the heart muscles relax and fill with blood. A dimer refers to a chemical structure formed from two subunits or molecules, commonly seen in biochemistry. Each of these terms highlights distinct concepts that do not pertain to the movement of molecules along a concentration gradient as diffusion does.