Since they are complex molecules, which contain many chemical bonds, organic molecules store a large amount of energy.
Glucose, for example, is the main energy source for the formation of ATP (adenosine triphosphate), a molecule that is necessary for several metabolic reactions. ATP is also an organic molecule and is the energy source for many biochemical reactions. Fat, proteins and some types of organic polymers, such as starch and glycogen, which are polymers of glucose, are energy reservoirs for organisms.