In order for a cell to function, it must be able to produce energy. This is accomplished by the mitochondria in all cells. Mitochondria are responsible for using oxygen and sugar from food in order to create ATP (adenosine triphosphate). The process of making ATP inside of these organelles is called aerobic respiration which releases lots of free heat as well as carbon dioxide, water vapor and electrons that can then combine with NAD+s found outside the mitochondria. These electrons help form new molecules or they go back into other reactions like those needed for DNA synthesis.