AP BIOLOGY

Detailed explanation-1: -All channel proteins and many carrier proteins allow solutes to cross the membrane only passively (“downhill”), a process called passive transport, or facilitated diffusion.

Detailed explanation-2: -Two classes of proteins that mediate facilitated diffusion are generally distinguished: carrier proteins and channel proteins.

Detailed explanation-3: -Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins.

Detailed explanation-4: -Channel proteins carry out the majority of facilitated diffusion. While the chemicals are still moving in the direction of their concentration (from high to low), they are given a passageway through the cell membrane. This allows them to move at near diffusion speeds.

Detailed explanation-5: -Both active transport and facilitated diffusion do use proteins to assist in transport. However, active transport works against the concentration gradient, moving substances from areas of low concentration to areas of high concentration.