What process describes the movement of molecules from an area of higher concentration to an area of lower concentration?

The process that describes the movement of molecules from an area of higher concentration to an area of lower concentration is diffusion. This natural movement occurs due to the random motion of molecules and continues until there is an equal distribution of the molecules across the space available.

In diffusion, no energy is required as the molecules move along their concentration gradient, which is a fundamental characteristic of this process. This phenomenon can be observed in various situations, such as when a drop of dye disperses in water or when oxygen diffuses into cells from the bloodstream.

Facilitated diffusion, while related to diffusion, involves the help of transport proteins in the cell membrane to assist larger or polar molecules in crossing cellular barriers. Osmosis specifically refers to the diffusion of water across a semi-permeable membrane, highlighting the focus on water molecules. Active transport, in contrast, requires energy to move molecules against their concentration gradient, which is not the case in simple diffusion. Thus, the correct answer, diffusion, captures the essence of the passive movement of molecules from high to low concentration without the need for external energy input.