Cellular respiration is a series of metabolic reactions which result in conversion of biochemical energy from nutrients into energy in the form of ATP. The general reaction of cellular respiration is: glucose (C6H12O) + oxygen (O2) → carbon dioxide (CO2) + water (H2O) + adenosine triphosphat (ATP). These reactions are catabolic (because large molecules, such as glucose, are broken down into small ones) and exothermic (because heat is released during the reaction).