Denitrification is the biological reduction of nitrate and nitrite to volatile gases, usually nitrous oxide or molecular nitrogen, or both. Denitrification is accomplished by bacteria capable of using nitrate in place of oxygen. Under aerobic conditions the bacteria oxidize carbohydrates to carbon dioxide and water. In the absence of oxygen these bacteria oxidize carbohydrates in nitrate respiration, yielding carbon dioxide, water, and the volatile gases, nitrous oxide and molecular nitrogen.