Chapter 9: Cellular Respiration?Harvesting Chemical Energy Concept 9.6 (176 ? 178) is not required knowledge for the AP? exam and is omitted. Overview: Life Is Work living cells require transfusions of energy from outside sources to perform their tasks energy enters into an ecosystem as sunlight and leaves as heat Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels Catabolic Pathways and Production of ATP breakdown of organic molecules is exergonic fermentation is a partial degradation of sugars that occurs without oxygen cellular respiration is the most prevalent and efficient catabolic pathway consumes oxygen and organic molecules (i.e. glucose) yields ATP to keep working, cells must regenerate ATP Redox Reactions: Oxidation and Reduction