Overview of Functional Groups in Organic Chemistry
Functional groups are combinations of atoms within organic molecules that are responsible for the reactivity of the molecules, and functional groups play a role in determining their physical properties. Although the chemical behavior of certain moeities may be modified by overall molecular structure, the approach to the reactivity of organic molecules through functional groups is a powerful analytical method. Every functional group has its own personality.

Functional Groups in Organic Chemistry on the MCAT
Understanding the behaviors of the main organic functional groups in organic chemistry is another way to describe, really, the discipline as a whole. Straight out organic chemistry comprises approximately one third of the Biological Sciences section of the MCAT typically, so there will be many instances on the test where your familiarity with the properties of various organic functional groups will play a role as a conceptual ground.