need and necessity of oxidation and reduction
Answers
To a chemist, redox merely refers to the transfer of electrons from one atom or molecule to another. One molecular part gains electrons and becomes reduced, and another part surrenders electrons and gets oxidized. So reduction is the opposite process of oxidation.
To a non-scientist, oxidation is equated with “burning” phenomena. The wood in a campfire oxidizes, the iron on your balcony railing oxidizes (rusts), and the sugar and fat that you eat oxidizes (you burn it for energy). This is why the concept of reduction is so hard for people to understand. While all these familiar oxidations are taking place, oxygen is reducing. But we do not talk about that part of the reaction, so it seems mysterious, or even techno-nerdish. But the electron equation is the transfer of electrons from the reduced wood, iron and food to oxygen.
This transfer of electrons is best not considered as a transfer of charge. Although it is on its most basic level, the resulting oxidized and reduced atoms regroup to minimize any charge at a molecular level. Take for example, the burning of gasoline in a car engine. The hydrocarbon fuel and the air it gets mixed with before it explodes can be thought of as carbon with charge zero, hydrogen with charge zero and oxygen with charge zero. After combustion, the carbon oxidizes to +4, the hydrogen oxidizes to +1 and the oxygen to -2. But the +4 carbon atoms are not found in a charged molecule, they combine with two -2 oxygens to make CO2 (carbon dioxide), which is neutrally charged. Two +1 hydrogen atoms combine with one -2 oxygen atom to make water (H2O), which is also neutrally charged. But the shift electrons (the redox reaction) has taken place, from carbon and hydrogen to oxygen, with a resounding release of energy.
To a biologist, redox reactions are especially interesting. They represent the fundamental energy that supports life. Some kind of redox reaction is a necessary and essential aspect of living metabolic systems, without which death occurs.
The “energy” that drives life is actually a redox potential. The potential is the difference between one atom or molecule with a high redox potential and another one with a low redox potential. For us warm-blooded animals, the primary redox potential that keeps us alive and conscious, is the potential between oxygen gas in the atomosphere and food. The fat-oxygen potential is quite high, almost to the level of hydrocarbon-air mixtures that power your automobile. The sugar-oxygen potential is roughly half as much.
But to microbes, the potential can be two different minerals, one of which comes out of a hydrothermal vent at the bottom of the ocean. It can be the difference between sugar and alcohol (the yeast-derived fermentation of beer and wine). It can be geothermal hydrogen and methane leaking up from the deepest reaches of the earth’s crust. It can be a truly amazing number of redox potentials.
And it can even be an entropy gradient that drives a redox-potential reaction.
Life is a special case of redox study because it is not redox neutral. Living systems are highly reduced. They have a large supply of electrons in the form of fuels like fat, sugar and amino acids, and antioxidants like NADH, NADPH, glutathione, ascorbate (vitamin C) and vitamin E. Most vitamins are reduced in their active states. Take folic acid, which is activated by doubly reducing it to tetrahydrofolate. Tetrahydrobiopterin is another example. They can be obtained from foods in their reduced states, or in their oxidized state and subsequently reduced.
A substantial portion of the total energy of life is devoted to simple maintenance of a highly reduced state within a more oxidized environment. Before the hydrogen (hydride) fuel on NADH is used to make ATP to power enzymes, some of it is diverted to NADPH for recycling antioxidants.
When warm-blooded animals (people) cannot maintain their energy from aerobic (O2 + fuel >> CO2) redox potentials, disease manifests. It’s one thing to burn glucose to lactic acid on rare instances where the demands of outracing a bear require more energy than is aerobically available, but it’s an entirely different thing to be continuously relying on the much smaller redox potential of fuel-lactate compared to fuel-oxygen.