All biological energy transactions involve the movement of electrons.
If an electron is moved away from its atomic center (of protons and neutrons), this is a non-spontaneous reaction and an input of energy is required.
If, on the other hand, an electron is moved closer to the atomic center of protons and neutrons, this is a spontaneous reaction and energy is liberated.
Within any biological molecule, such as sucrose, electrons that carry a certain amount of energy are shared by the various constituent atoms. For examples, there are lots of carbon and hydrogen atoms in the sucrose molecule. In each covalent bond holding them together, two electrons are shared.
These electrons contain a relatively high level of energy and are equally shared by both the carbon and hydrogen atoms. Similarly, the electrons in an oxygen molecule also hold a lot of energy and are equally shared by both oxygen atoms.
When, however, the oxygen molecule reacts with the sucrose molecule, the atoms rearrange themselves into two new substances - carbon dioxide and water.
In these molecules, the electrons are shared differently. The electrons are now much closer to the oxygen atom that hey are to either the carbon or hydrogen atoms. They have been moved toward the atomic center of the oxygen atom, and thus to a lower energy state.
The extra energy is given off. The breakdown of sucrose, therefore, is a spontaneous reaction that obeys the second law of thermodynamics.
Inside the sugar cane plant, sucrose molecules combine with oxygen in a process called respiration. The basic principles of respiration are quite simple.