The side groups are what make each amino acid different from the others. Of the 20 side groups used to make proteins, there are two main groups: polar and non-polar. These names refer to the way the side groups, sometimes called "R" groups, interact with the environment.
"*Because the lymphatic system collects excess tissue fluid, if it were not working, swelling (edema) would occur in the tissues. The thymus cleanses the blood from the cardiovascular system of cellular debris and bacteria."
