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

The correct answer, diffusion, is a fundamental process that describes the movement of molecules across a membrane or through a medium from an area of higher concentration to an area of lower concentration. This movement occurs spontaneously due to the inherent kinetic energy of the molecules, meaning they move along a concentration gradient without the need for external energy or assistance.

Diffusion is essential for various biological processes, including the exchange of gases in the lungs, nutrient uptake by cells, and even the dispersal of scents in the air. It relies on the principle that systems tend to move toward equilibrium, where the concentration of substances is balanced on both sides of a barrier or within a given space.

In contrast, processes like active transport require energy input to move substances against their concentration gradient, from an area of lower concentration to higher concentration. Facilitated diffusion also allows molecules to cross membranes but does so through specific transport proteins and remains passive, meaning it does not require energy and still depends on the concentration gradient. Endocytosis refers to a mechanism by which cells engulf substances in vesicles, a much different process that involves membrane folding and is also energy-dependent.

Understanding diffusion is crucial for grasping how substances behave in biological systems and the principles of cellular transport mechanisms.