What process involves the transport of substances across a plasma membrane with the assistance of carrier proteins, but does not require energy?

Facilitated diffusion is the process that involves the transport of substances across a plasma membrane with the assistance of carrier proteins, and importantly, it does not require energy. This is a type of passive transport where molecules move down their concentration gradient, meaning they move from an area of higher concentration to an area of lower concentration. The presence of specific carrier proteins in the membrane allows for the transport of polar or larger molecules, such as glucose or ions, which cannot easily pass through the lipid bilayer on their own.

In contrast, active transport requires energy to move substances against their concentration gradient, while osmosis is specifically the movement of water through a selectively permeable membrane. Simple diffusion refers to the movement of small or nonpolar molecules directly through the lipid bilayer without the need for proteins, relying solely on the concentration gradient.