What are water channels and what is osmosis?
Recently scientists discovered that even water molecules sometimes use special proteins to cross cell membranes. Water is a very small polar molecule that is not fat soluble and that sometimes sneaks or squeezes between the phospholipid molecules in the bilayer to cross cell membranes. However certain cells need water faster and have additional special water transport proteins (known as water channels). Water crosses cell membranes both through the lipid bilayer portion and through the protein water channels by passive transport (downhill by diffusion). The movement of water molecules by diffusion from the higher concentration of water molecules to the lower concentration of water molecules is known as osmosis. [In order to determine where there are more water molecules, one needs to consider what is dissolved in the water. A concentrated solution has many salt or sugar or other molecules dissolved in it (and thus a lower number of water molecules). A dilute solution has fewer salt or
