Using the diagram of the cell membrane, the chemistry of phospholipids, amino acids, proteins and diglycerides was presented. The chemical structure of amino acids was presented and then shown how they form proteins. The structure of phospholipids was presented and shown how it fits into the structure of the cell membrane, and the function it performs. Antigens and receptor sites was explained in terms of "physical fit" and how the binding stimulates the reaction in the cell to that specific chemical.