Cracking the AP Biology Exam


The Chemistry of Life


Now that we’ve discussed chemical compounds in general, let’s talk about a special group of compounds. Most of the chemical compounds in living organisms contain a skeleton of carbon atoms. These molecules are known as organic compounds. By contrast, molecules that do not contain carbon atoms are called inorganic compounds. For example, salt (NaCl) is an inorganic compound.

Carbon is important for life because it is a versatile atom, meaning that it has the ability to bind with other carbons as well as a number of other atoms. The resulting molecules are key in carrying out the activities necessary for life.

To recap:

  • Organic compounds contain carbon atoms.
  • Inorganic compounds do not contain carbon atoms (except carbon dioxide).

Now let’s focus on four classes of organic compounds central to life on earth:

  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic acids