Glucose is the most common fuel molecule in animals, plants, and microbes. It is the starting molecule for glycolysis, which results in the partial oxidation of glucose and the synthesis of a relatively small amount of both ATP and reduced electron carriers. Glycolysis literally means “splitting sugar,” an apt name because in glycolysis a 6-carbon sugar (glucose) is split in two, yielding two 3-carbon molecules. The process is anaerobic because oxygen is not consumed. Glycolysis evolved very early in the evolution of life, when oxygen was not present in Earth’s atmosphere. It occurs in nearly all living organisms and is therefore probably the most widespread metabolic pathway among organisms.