The hydrocarbon chains of the two fatty acids function as hydrophobic non-polar tails of the phospholipid molecule. The phosphate and the additional group behave as hydrophilic polar head of the molecule. In the aqueous medium, the phospholipid molecules arrange themselves to form a thin double layer. The polar hydrophilic heads of the molecules form the two surfaces which are in contact with water. The hydrophobic or non-polar tails of the phospholipid molecules are towards the centre of the bilayer. "