Glucose oxidation is a chemical process that provides energy for an organism to carry out all of its required activities. During this process, glucose from food is broken down into carbon dioxide and water, and energy is released. The process of releasing energy from food is called respiration, or cellular respiration as it is a series of steps that take place within living cells. It is important to not confuse respiration, or oxidizing glucose, with breathing.

A simple sugar molecule, glucose is used to build more complex carbohydrates, like starch and cellulose. It has a ring structure and its chemical formula is C6H12O6, or six carbon atoms, 12 hydrogen atoms, and six oxygen atoms form one molecule of glucose. The bonds holding the glucose molecule together are high energy bonds, so when they are broken, energy is released and available for the cell to use.

Glucose oxidation is an aerobic process, which means it needs oxygen for the chemical reaction to occur. Oxidation is actually any reaction where oxygen is combined with another molecule; the molecule that is combined with the oxygen molecule is said to be oxidized. For the oxidation of glucose, one molecule combines with six oxygen molecules to produce six carbon dioxide molecules, six water molecules, and 2,830 kilojoules (kJ) of energy.

The energy released by glucose oxidation is often not used directly by that cell. Instead, it is stored as a chemical source of energy. Most commonly, the energy is stored in adenosine triphospate (ATP) molecules.

At each stage of the oxidation of the glucose molecule, the energy that is released is used to combine a phosphate ion to adenosine diphosphate (ADP). In total, from one molecule of glucose, 38 molecules of ATP are formed. When the energy is needed by the cell, the ATP molecules are broken down to ADP and phosphate ions, releasing the energy stored in the molecule of ATP.

Within cells, this energy is not released all at once. Glucose oxidation is actually a complex reaction that has a number of different steps. At each step, different enzymes are used to carry out a different part of the process and part of the total energy is released. The process has three general steps: glycolysis; the Krebs cycle, or the citric acid cycle; and the electron transport system.

Glycolysis takes place within the cytoplasm of all cells. During this stage, the glucose molecule is broken down into two pyruvate, or pyruvic acid, molecules and eight ATP molecules are produced. The Krebs cycle produces six ATP molecules, but the pyruvate is broken down to carbon dioxide and hydrogen atoms are released for use in the electron transport system. This final stage of glucose oxidation takes place within the mitochondrion and is what releases the most energy. As the hydrogen atoms are oxidized and form water molecules, 24 ATP molecules are produced.