What distinguishes facilitated diffusion from simple diffusion?

Facilitated diffusion is characterized by its dependence on specific transport proteins that assist in the movement of molecules across a cell membrane. This process is essential for transporting larger or polar molecules, such as glucose or ions, which cannot easily pass through the lipid bilayer of the membrane due to their size or charge.

The presence of these proteins allows for a more efficient and selective transport mechanism, ensuring that essential molecules can enter or exit cells in response to concentration gradients. Unlike simple diffusion, which occurs directly through the membrane without assistance, facilitated diffusion relies on these integral membrane proteins, functioning as channels or carriers, to help move substances in a direction favorable to their concentration gradient.

This distinction is crucial in understanding how cells maintain homeostasis and regulate their internal environments effectively. The other options do not accurately describe facilitated diffusion; it does not require energy, does not occur solely in liquid environments, and is not necessarily faster than simple diffusion, as the rate can vary depending on the specific conditions and molecules involved.