In a cell, why must NADH be reoxidized? How does this happen in an organism that uses respiration? Fermentation? 2. Explain the chemiosmotic mechanism of ATP generation. How does oxidative phosphorylation compare with substrate level phosphorylation found in glycolysis and Kreb’s cycle? 3. Which of the following yields the greatest energy for a cell: fermentation, anaerobic respiration, or aerobic respiration? Which yields the least? Why? 4. Explain what happens to glucose during glycolysis and respiration in terms of oxidation and reduction.