Passive transport

Passive Transport is the movement of substances across a semipermeable membrane without the input of cellular energy. There are 4 major types of passive transport: diffusion, facilitated diffusion, filtration and osmosis.

Facilitated diffusion works by concentration gradients of substances that would not ordinarily be able to cross the lipid membrane. This diffusion is facilitated by the presence of a channel protein.

Ion Channels are transmembrane proteins that facilitate the movement of ions across the membrane. The pore of the channels contains specific amino acid residues that foster the movement of selective ions across.