Figure 1.5

   Generation of metabolic energy

Glycolysis is the anaerobic breakdown of glucose to lactic acid. Photosynthesis utilizes energy from sunlight to drive the synthesis of glucose from CO₂ and H₂O, with the release of O₂ as a by-product. The O₂ released by photosynthesis is used in oxidative metabolism, in which glucose is broken down to CO₂ and H₂O, releasing much more energy than is obtained from glycolysis.