Mitochondria are the powerhouses of the cell. They supply nearly all the required biological energy. Only the mitochondria are fully capable of converting pyruvic acid to carbon dioxide and water. Mitochondria are the respiratory centres of the cell. Cell respiration can be divided into four phases: 1) glycolysis, 2) oxidation of pyruvic acid, 3) krebs citric acid cycle and 4) oxidative phosphorylation through the hydrogen/ electron transport system. Glycolysis involves the breakdown of glucose to pyruvic acid. The enzymes for glycolysis are found in the cytosol, outside the mitochondrion. During oxidation of pyruvic acid, Pyruvic acid is degraded to acetyl-CoA, with the liberation of a pair to hydrogen.
Consider the mitochondrion as the power plant of a cell, which provides energy to all other organells. Without the energy the nucleus and the ribosomes would not be able to carry out the protein synthesis,the lysosomes would stop functioning, the active transport accross the cell membrane would stop and the accumulated waste would poison the cell.The number of mitochondria in the cell is directly proportional to the energy demands of the cell.