ATP is the abbreviation for adenosine triphosphate, a high-energy molecule that sometimes is called the universal energy carrier of cells. ATP is vital to the function of all cells on earth.
Plants are the most well-known photosynthetic organisms. However, many types of bacteria and protozoa also are photosynthetic. Animals, which include human beings, are not capable of photosynthesis.
Photosynthesis consists of a light-dependent phase (light reactions) and a dark phase (dark reactions).
During the light reactions of photosynthesis, energy from light is used to transfer electrons from water to a special electron-acceptor molecule called NADP+. This releases oxygen (O2), while creating a high-energy molecule called NADPH. This produces a proton gradient across special membrane folds known as thylakoids. Energy from the gradient is then used to make ATP from a lower energy molecule, ADP.
Unlike the light phase of photosynthesis, which produces energy, the dark phase makes use of the energy that has been acquired. In the dark phase, ATP and NADPH are used to convert carbon dioxide into sugar.