Kinds of lipids. Lipids are classified as simple lipids or complex lipids, according to their structure. Simple lipids contain only carbon, hydrogen, and oxygen. They consist of an alcohol in combination with certain organic acids containing a variable number of carbon atoms. Waxes, another common group of simple lipids, contain an alcohol molecule that is larger than the glycerol molecule.
Complex lipids have a more complicated structure than simple lipids.
Phospholipids are found in all bacteria, and in the cells of all plants and animals. They are most plentiful in sperm, eggs, embryos, and brain cells. A molecule of phospholipid contains a molecule of glycerol, a phosphate ion, and two molecules of fatty acid. Most phospholipids also have a nitrogen compound. Some contain inositol, a substance found in vitamin B complex.