The basic building blocks of a cell membrane are phospholipids. Phospholipids contain a hydrophobic (insoluble in water) end made up of two fatty acid chains of nonpolar molecules such as carbons and hydrogens. The other end is hydrophobic (soluble in water) and contains polar phosphate molecules. These phospholipids are arranged in a bilayer with their hydrophilic end group exposed to water on each side of the membrane and the hydrophobic nonpolar molecules protected inside the double layer.
