Carbon is the main constituent of all living cells. It has chemical properties that make it the most important biological element. For instance, it forms strong chemical bonds and can form single bonds with up to four other atoms. It can bond to itself. It can also form double and triple bonds. Carbon is one of the only elements, because of its bonding properties, that can create long chain-shaped molecules or ring shaped molecules. These carbon rings and chains form the basis for the fats (fatty acid chains), carbohydrates, nucleic acids (DNA and RNA), and proteins that serve as the basis of life. (Although elements, such as oxygen, hydrogen, phosphorus, sulfur and others are also needed).
The study of carbon molecules is called organic chemistry, and there is a subset, biochemistry, that deals with the carbon molecules in living organisms.
Even outside of the realm of biological life, carbon is important, especially to industry. Carbon is a critical component of fuel, such as gasoline or coal. Diamond (pure carbon) is used for drills as well as jewelry, and graphite, another form of carbon, is used in pencils. Scientists are in the process of using carbon to make nanotubes and other compounds that can be used in computers, bullet-proof armor, and other high-tech uses.