Why is ATP produced continuously in such large quantities?

ATP is constantly being produced in every mitochondrion of the cell, but it can't be stored within it. This is directly related to the properties of this important molecule - the phosphate bond between the three phosphate molecules (which, combined with the adenine base and ribose sugar, form an ATP molecule) can easily be broken down, releasing energy. This is catalysed by a specific enzyme called ATP ase, which hydrolises the bond between the third phosphate and the rest of the molecule, which results in a formation of ADP (adeninodiphosphate molecule containing two phosphate groups), one inorganic phosphate (P_i) and some surplus energy. This energy can be used in numerous processes maintaining the life of an organism, such as the movement of myosin heads in muscle contraction or reabsorption of calcium ions into the endoplasmic reticulum. It is therefore important to maintain a continuous supply of ATP containing these high-energy phosphate bonds.