Which process describes the passive movement of molecules from a higher concentration to a lower concentration across the plasma membrane?

The process that describes the passive movement of molecules from a higher concentration to a lower concentration across the plasma membrane is facilitated transport. This mechanism involves the movement of substances down their concentration gradient, requiring no energy input from the cell. It occurs through specific transporter proteins embedded in the membrane that assist in the passage of molecules that are typically unable to diffuse freely due to their size, polarity, or charge.

In facilitated transport, the binding of the molecule to the transporter protein induces a conformational change, allowing the substance to cross the membrane. This contrasts with active transport, which requires energy to move substances against their concentration gradient. Osmosis specifically refers to the movement of water across a semi-permeable membrane, while exocytosis is a process that involves the expulsion of materials from the cell via vesicles, which is not a passive transport mechanism. Thus, facilitated transport is accurately characterized by the passive diffusion of molecules aided by transport proteins, providing an essential route for cells to control their internal environments efficiently.