An exergonic reaction will release energy from the reaction, while an endergonic reaction will absorb free energy from its surroundings. In order for an endergonic reaction to go to completion it needs an outside source of energy. In the cell this energy source comes from the chemical compound ATP. ATP helps the cell carry on 3 main types of work. Mechanical ( cell movement), chemical ( anabolism ), and transport ( pumping materials into and out of the cell ).