Higher life forms depend on oxygen to create energy for the cells. But there are unicellular microorganisms that fear oxygen because of its ability to also destroy life. This process is called “oxidation” and relies on oxygen’s unique ability to attract (or “receive”) electrons from other atoms and molecules.
Surrounding the nucleus of atoms are electrons that spin in orbits. When an orbit lacks a set of “paired electrons”, that orbit will make every effort to attach itself to another atom, or group of atoms, so that the orbiting electrons become more stable. These atoms may even “steal” electrons from other atoms or molecules. (Molecules are a group of two or more atoms jointed together).
To help visualize the remarkable potential of electrons, imagine yourself spinning a golf ball around yourself and that this golf ball is connected to a spring. The golf ball represents the electron and the place where you are standing is where the atom’s nucleus would be. If you spin the golf ball around you in a constant speed, the electron will be at the same distance from you, spinning at the same speed you are turning. If you start to spin harder, by putting more energy into your spin, you'll notice that the golf ball will move away from you and the spring will expand. Likewise, if you spin more slowly, the golf ball will be closer to you and the spring will contract. In the same way, with changes in energy, an electron can occupy a different orbit around its nucleus.
The smallest of these orbits represents the lowest energy that the electron can possess. This lowest energy state is known as the “ground state.” If the electron absorbs energy of the right amount, (such as visible, infrared (heat), or ultraviolet light,) the electron can jump to a higher orbit or "energy level" in the atom. With the electron in a higher orbit, the atom is said to be in the "excited state." At this point, the electron can fall back to a lower energy orbit or even the ground state. As it falls one orbit at a time, it emits a certain amount of energy, which may also be in the form of light, heat, or so on.

It is this remarkable movement and exchanging of electrons on an atomic and subatomic basis that actually serves as a defense mechanism for our immune system as well as a process to control dangerous microorganisms that cause every known disease on the planet today.