BIO101: Introduction to Molecular and Cellular Biology

Any living cell is able to extract energy from fuel and temporarily store that energy in the form of ATP, or a similar energy currency. The primary processing of fuel is called glycolysis. Only certain cells under the right conditions are able to continue where glycolysis leaves off, allowing much more usable energy to be extracted from the fuel.

That additional processing of energy is called cellular respiration. Glycolysis and cellular respiration both extract usable energy from fuel by undergoing oxidation/reduction (or redox) reactions.

Oxidation refers to the loss of electrons from a particle (such as a fuel molecule), whereas reduction is the gain of electrons. Since electrons are not destroyed in chemical reactions, oxidation occurs only if reduction also occurs. When something is oxidized (loses electrons), something else gets reduced (gains electrons).

Organisms extract energy from fuel molecules by oxidizing these fuel molecules. In cellular respiration, there is a substance (external to the process) that ultimately accepts the electrons that have been removed from the fuel. For aerobic organisms, that substance is oxygen, and when oxygen accepts those electrons (along with protons) from the fuel molecules, the oxygen gets reduced into water. Cellular respiration is important because it allows for maximal oxidation of fuels, which maximizes the amount of energy that can be extracted and stored as ATP.

Watch this video for an overview of cellular respiration. After you watch, you should be able to explain the role of cellular respiration.