Question

Energy is released to be used by a cell when a phosphate group is

Answer 1

hydrolyzed

Answer 2

"a process called coupling which means the two reactions occur at the same time and at the same place, usually utilizing the same enzyme complex. Release of phosphate from ATP is exothermic (a reaction that gives off heat) and the reaction it is connected to is endothermic (requires energy input in order to occur). The terminal phosphate group is then transferred by hydrolysis to another compound, a process called phosphorylation, producing ADP, phosphate (Pi) and energy."
Source: http://www.trueorigin.org/atp.asp

Answer 3

Energy is normally released when a molecular bond is broken. ATP is the major source of energy transfer in the cell, and even has its own organelle devoted to making it, the mitochondria. The mitochondria in your body uses the energy from sugars to connect ADP to a phosphate group to make ATP which is then transferred anywhere in your body that needs work done. When it gets there it transfers its energy by breaking apart back into ADP and phosphate that get recycled again!

The term hydrolysis comes from hydro meaning water, and lyse meaning break. This is just a fancy way of saying water was used to help break the bond. If you think of the bond between ADP and phosphate to make ATP as ADP holding hands with phosphate, when they no longer are bonded to each other they still have a hand out wanting to hold onto someone. So they end up grabbing onto H2O and ripping apart one hydrogen from the other hydrogen and oxygen and hold onto them instead.