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Unformatted text preview: Bio1A Dr. McCray Lec 7 Complete Notes 1 Chapter 9 Cellular Respiration: Harvesting Chemical Energy Energy Flow a Energy flows into an ecosystem as sunlight and leaves as heat a Photosynthesis generates oxygen and organic molecules , which are used in cellular respiration a Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work Fig. 9-2 Catabolic Pathways and Production of ATP a Several processes are central to cellular respiration and related pathways a The breakdown of organic molecules is exergonic a Fermentation is a partial degradation of sugars that occurs without oxygen a Cellular respiration consumes oxygen and organic molecules and yields ATP a Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy (ATP + heat) Redox Reactions: Oxidation and Reduction a The transfer of electrons during chemical reactions releases energy stored in organic molecules a This released energy is ultimately used to synthesize ATP Redox a Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions a In oxidation , a substance loses electrons, or is oxidized a In reduction , a substance gains electrons, or is reduced (the amount of positive charge is reduced) Redox Terminology a The electron donor is called the reducing agent a The electron receptor is called the oxidizing agent a Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds a An example is the reaction between methane and oxygen Fig. 9-3 Oxidation of Organic Fuel Molecules During Cellular Respiration a During cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced : Bio1A Dr. McCray Lec 7 Complete Notes 2 Stepwise Energy Harvest via NAD + a In cellular respiration, glucose and other organic molecules are broken down in a series of steps a Electrons from organic compounds are usually first transferred to NAD + , a coenzyme a As an electron acceptor, NAD + functions as an oxidizing agent during cellular respiration a Each NADH (the reduced form of NAD + ) represents stored energy that is tapped to synthesize ATP Fig. 9-4 Electron Transport Chain...
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