text: Trigylcerides are composed of two types of molecules: glycerol and 3 fatty acids.\n\nPhospholipids are similar to triglycerides in that they contain glycerol and fatty acids, too. But, the big difference is that phospholipids are made up of 1 glycerol molecule and only 2 fatty acid molecules (not 3!)\n\nThis is a big difference because in place of the third fatty acid, phospholipids have a polar group attached to the glycerol molecule. Remember, triglycerides were entirely hydrophobic because all three positions on the glycerol molecule were taken up by nonpolar fatty acids. But, phospholipids have a polar group in one place on the glycerol molecule, making phospholipids partly hydrophilic; the polar group helps to form the polar head.  The two fatty acids, maintain a hydrophobic portion of the phospholipid, the tails.