What is the process called when molecules move from an area of higher concentration to an area of lower concentration?

The process in which molecules move from an area of higher concentration to an area of lower concentration is known as diffusion. This movement occurs because molecules tend to spread out evenly in a space, seeking a state of equilibrium where concentration is uniform. Diffusion is a passive process; it does not require energy input because it relies on the natural kinetic energy of the molecules.

Osmosis, while related to the movement of water molecules, specifically refers to the diffusion of water across a semipermeable membrane. Active transport, on the other hand, is an energy-dependent process used to move molecules against their concentration gradient, from lower to higher concentration. Endocytosis refers to the process by which cells engulf substances, bringing them into the cell, and does not involve the direct movement of molecules based solely on their concentration gradients. Thus, diffusion is the correct term for this specific type of movement based on concentration gradients.