All living organisms, from bacteria, fungi, spinach and worms to crocodiles and humans, use ATP for energy conversion.
Originally, the energy comes from the sun.
Plants capture it during photosynthesis and convert it to chemical energy as ATP. Using this energy, plants produce carbohydrates, fats and proteins which are eaten by animals and human beings.
In metabolism, the food is broken down and the energy released is used to make ATP.
Energy is interconverted between various forms. Compare this with the idea of different currencies, only one of which is accepted at a time. ATP is an energy currency.
