Lipids are organic compounds that are greatly diverse in their structure and properties. Lipids constitute of fatty acids (triglycerides), waxes, sterols as well as phospholipids. The photograph shows a picture of olive oil, an unsaturated triglyceride. Fatty acids are hydrophobic in nature. For example, the phospholipids, with a hydrophilic head and two hydrophobic tails, form a lipid bilayer in the cell membrane.