Lipids are membrane constituents and function as carbon stores
Lipids subdivide into glycerolipids, shingolipids, and steroids. Glycerolipids are fatty acid esters of glycerol (Fig. 15.1).Triacylglycerols (also called trig-lycerides) consist of a glycerol molecule that is esterified with three fatty acids. Whereas in animals triacylglycerols serve primarily as an energy store, they function in plants mainly as a carbon store in seeds, which are used by humans as vegetable oils. In polar glycerolipids, the glycerol is esterified with only two fatty acids, and a hydrophilic group is linked to the third -OH group. These polar lipids are the main constituents of membranes.