Biology Chapter 9 Notes: Fermentation: Partial degradation of sugars or other organic fuels which occurs without the use of oxygen to generate chemical energy. However most prevalent and efficient catabolic pathway is aerobic respiration, in which oxygen is consumed along with the organic fuel. Remember that a catabolic pathway breaks down compounds in order to release energy. Some prokaryotes carry out cellular respiration, most eukaryotes do however. Anaerobic Respiration: Using a substance other than oxygen to harvest chemical energy. During the redox reaction of cellular respiration, glucose is oxidized to carbon dioxide, and oxygen is reduced to water. The electrons lose potential energy along the way and energy is released. Hydrogen is transferred from glucose to oxygen. **In respiration the oxidation of glucose transfers electrons to a lower energy state, liberating the energy that becomes available for ATP synthesis. If energy is released from a fuel all at once, energy cannot be harvested as efficiently, for example if a gasoline tank explodes, we cannot drive a car very well. In the case of cellular respiration, glucose is not harvested all at once immediately, the harvesting of glucose for chemical energy occurs in multiple steps. At key steps electrons are stripped from glucose, each electron will travel with a proton (hydrogen atom). Hydrogen atoms are not directly transferred to oxygen, but instead to an electron carrier NAD+. *Enzymes called dehydrogenases remove a pair of h atoms (2 electrons and 2 protons) from the substrate, therefore oxidizing it. 1 h+ released into solution, 2 e and 1 P+ given to coenzyme NAD+. Electron transfer from NADH to oxygen is an exergonic reaction, electrons are cascaded down the chain releasing a small amount of energy at each step until the electrons reach oxygen. Stages of Cellular Respiration: Glycolysis: Investment Phase Occurs in the cytosol, begins with the breaking of glucose into two molecules of a compound called pyruvate.