ATP stands for Adenosine Triphosphate. It is the primary energy carrier (a universal metabolic currency) in all living organisms. Energy that is metabolized ([[metabolism]]) from food and light sources is stored in the form of ATP. When a cell requires energy, ATP is broken down through hydrolysis into ADP (adenosine diphosphate). Energy is released by breaking the bond of the third phosphate. The reverse process from ADP to ATP uses energy from food and oxidative respiration in mammals and photosynthesis in plants. > The cycle of releasing energy from the breakup of ATP into ADP and its recycling back from ADP to store energy in ATP forms a continuous loop process much like the charging and recharging of a battery. > – [[Reference Notes/Scale]] At any one time our bodies contain only about 250 g of ATP. But every day, we make about 80 kg of ATP, producing and recycling our body weight in ATP. We require this amount of ATP to stay alive and power our bodies at the rate of 90 watts. ATP can be measured using bioluminescence. In the tail of a firefly, ATP reacts with luciferase to give light. The amount of light can be quantified in a luminometer. Since ATP is present in all microbial cells, this is also a good way to measure microbiological content in fluids.^[LuminUltra. “What Is ATP and What Does It Do?,” October 19, 2016. https://www.luminultra.com/what-is-atp-and-what-does-it-do/.]