Which process describes the passive movement of molecules from high to low concentration?

The passive movement of molecules from an area of high concentration to an area of low concentration is best described by diffusion. This process occurs naturally, driven by the concentration gradient, meaning that molecules move spontaneously without the input of energy. This is essential in many biological processes, such as the exchange of oxygen and carbon dioxide in the lungs or the movement of nutrients and waste products across cell membranes.

In diffusion, molecules will continue to move until they reach an equilibrium where the concentration is balanced across the space. This natural tendency of molecules to spread out is fundamental to many cellular functions. Understanding diffusion provides a clear insight into how substances move within biological systems, emphasizing its critical role in maintaining homeostasis and facilitating metabolic processes.