Photosynthesis Energy Transformations ATP is the energy molecule used in all living things, so supplies must be constantly replenished. energy must be added to make ATP, thus ATP formation is an endergonic reaction. ADP + P + energy ---? ATP the addition of a phosphate molecule to ATP is called phosphorylation ATP ---? ADP + P + energy the removal of a phosphate molecule from ATP gives off energy and is called dephosphorylation Electron Transport System (ETS) is the means by which energy production occurs within cells. It is a series of progressively stronger electron acceptors. Each time an electron is transported, energy is either released or absorbed. This is how most of the ATP in plants and animals is formed Redox Reactions