Final answer:
Phosphorylation is the process of adding a phosphate group onto ADP to form ATP. ATP is the energy currency of the cell and is used to power various cellular processes.
Step-by-step explanation:
Phosphorylation is the process of adding a phosphate group onto ADP to form ATP. This process requires energy because phosphate groups are negatively charged and repel each other when arranged in series. ATP is the energy currency of the cell and is used to power various cellular processes through the release of phosphate groups in a process called dephosphorylation.