Carbon Dioxide is the molecule of one carbon and two oxygen atoms. It is a major waste product of respiration, and is created when dissolved oxygen in the blood is used to create ATP, the basic unit of biological energy. Glucose is stored in cells as fuel, and is made up of carbon, hydrogen, and oxygen (C6-H12-O6). The glycolysis process breaks apart the chemical bonds holding these atoms together by oxidation, using the dissolved oxygen in the blood; the breaking of these bonds releases their stored energy, which is converted to ATP and used throughout the body as units of energy. The carbon atoms left behind are waste, and they bond with leftover oxygen atoms to create carbon dioxide. Since carbon dioxide is toxic in large amounts, it is absorbed by the blood and carried back to the lungs where it is released in exhalation. Carbon dioxide is not produced until the chemical bonds of the glucose are broken, a process which uses 2 ATP, at which point the waste carbon attaches to loose oxygen atoms; the process is very efficient, as an expenditure of 2 ATP produces around 36 ATP to reuse elsewhere in the body. Through this process, the human body creates approximately one kilogram of carbon dioxide each day.