Describe the structure and function of fatty acid molecules, including the difference between saturated and unsaturated fatty acids

A fatty acid has two main parts: 1) a long hydrocarbon chain and 2) a carboxylic acid group. The hydrocarbon chain is how we can tell if it is saturated or not. If there are carbons-carbon double bonds, then it would be unsaturated. Saturated fatty acids have no double bonds. 
Fatty acids are very important to the body for several reasons. They are essential to the structure of the cell membrane, they can be used for long term energy storage, healthy brain function, targeting molecules for many proteins, as well as cellular messengers. 

Bis the correct answer.