Chapter 9 Read Chapter 9 Biochemical pathways are series of chemical reactions. Each step involves only a small change but the process as a whole produces major change. One of the greatest secrets, how cells use food as a source of energy, has become reasonably well understood only recently. At the end of glycolysis most of the energy originally stored in glucose is still present in the pyruvate molecules.
Glycolysis takes place in virtually all living cells.
In the presence of oxygen the products of glycolysis go on to the Krebs cycle and the electron transport chain. If oxygen is not present fermentation takes place. When we inhale, we bring in oxygen for this process. When we exhale we expel the CO 2 that is formed as a by-product. The passage of electrons through the electron transport chain is an energy releasing process, and this energy is used to produce a proton gradient.