What is Lipid bilayer?
[[File:Lipid bilayer section.gif|right|thumb|300px|This fluid [[lipid]] bilayer cross section is made up entirely of [[phosphatidylcholine]].]] [[File:Phospholipid_TvanBrussel.jpg|thumb|300px|Phospholipid]] '''Lipid bilayers''' form [[cell membrane]]s. They form a continuous sheet around all cells, and they surround most [[cell organelles]]. Lipid bilayers form automatically from '''phospholipids''' by [[self-organisation|self-assembly]]. The [[phospholipid]]s have heads which mix with water and tails which reject water. So the tails come together in the centre of the double layer, and the heads on the outside are surrounded by water. The lipid bilayers stop most water-soluble (hydrophilic) molecules passing through. They also stop most [[ions]]. In cells, [[proteins]] are put in the bilayer by [[enzymes]]. The proteins decide which [[molecules]] come in and which go out of the cell. For example, cells control salt concentrations and pH by pumping ions across their membranes using proteins called [[ion pump]]s. [[Category:Biochemistry]] [[Category:Cell biology]] [[Category:Plant anatomy]] {{multistub|biology|chemistry}}