Is facilitated diffusion considered an active or passive process?

Facilitated diffusion is indeed classified as a passive process, which means it does not require any energy input from the cell. Instead, this process relies on the natural tendency of molecules to move down their concentration gradient, which is the difference in concentration across a membrane. When substances are more concentrated on one side of the membrane, they will move towards the area of lower concentration until equilibrium is reached.

In facilitated diffusion, this movement is assisted by specific transport proteins, such as carrier proteins or channel proteins, that help larger or polar molecules cross the lipid bilayer of the cell membrane. The key point is that because the movement is along the concentration gradient, no additional energy (like ATP) is needed for this transport, distinguishing it from active transport processes, which do require energy to move substances against their concentration gradient.

Although some of the other options mention active processes or specific conditions of transport, facilitated diffusion is fundamentally characterized by this passive characteristic, simplifying the transport of crucial molecules like glucose and ions into and out of cells without energy expenditure.