Thus, cells need a continual outside source of energy. All organisms use the organic molecules in their food for energy and for building materials for growth and repair. Some of the energy released is used to do work, the rest is dissipated as heat.
Respiration is exergonic.
The main function of cellular respiration is to provide energy for ATP synthesis. In general, organic molecules that have an abundance of hydrogen are excellent fuels because they are rich in high energy electrons. Living systems are experts at energy conversion. When electrons are transferred from glucose to these electron carriers, they lose very little potential energy. Requires an input of 2 ATP molecules.