Plasma membranes are located around the edge of animal cells and surround the cytoplasm and other organelles. They are made up of a phospholipid bilayer which consists of two layer of phospholipids with the hydrophobic heads on the outer layers and the hydrophylic tails on the inner layers. lipid soluble molecules can diffuse straight through the bilayer, water can osmosise through as well. The phospholipid bilayer contains intrinsic and extrinsic proteins. The intrinsic proteins go all the way through the bilayer whereas extrinsic proteins only go through the outer phospholipid layer. Extrinsic Proteins are used for recognition of the cell and usually have a glycoprotein attached for the recognition. Intrinsic Proteins are for allowing molecules through. Ways the proteins are designed to allow molecules through are: Protein pump, Protein Channel, Gated protein channel.