Channel protein

Unique membrane transport proteins move substances across cell membranes by forming a continuous pathway across the membrane. Carrier and channel proteins are the two major classes of such membrane transport proteins.

Bilayer

All biological cell membranes are primarily made up of a bilayer of phospholipids. These act as protective gatekeepers that separate the cell's interior from the outside environment.

Water

Water channel proteins called aquaporins move water molecules across the membrane much more rapidly than they can diffuse through the phospholipid bilayer.