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Chapter 9 - Chapter 9 Cellular Respiration Harvesting...

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Chapter 9 Cellular Respiration – Harvesting Chemical Energy Energy flows through ecosystems: the chemicals within an ecosystem are recycled. Concept 9.1 Catabolic pathways yield energy by oxidizing organic fuels. Cellular Respiration and Fermentation are catabolic pathways. Fermentation is the partial degradation of sugars that occurs without the use of oxygen. Both the electron donor and the electron acceptor are organic compounds. Cellular Respiration is an ATP-producing pathway in which the ultimate electron acceptor is an inorganic molecule, usually oxygen. Aerobic respiration – the most common and efficient catabolic pathway. The reactants are an organic fuel and O 2 . Performed by cells of most eukaryotic and prokaryotic organisms. Figure on Moodle Anaerobic respiration – performed by some prokaryotes, and involves a similar pathway in which O 2 is replaced by some other substance. Redox reactions release energy when electrons move closer to electronegative atoms. Chemical reactions which involve a partial or complete transfer of electrons from one reactant to another. Two Types: Oxidation is the loss of electrons from one substance. 1. Reducing Agent Reduction is the gain, or addition of electrons to a substance. Called this because it reduces the amount of positive charge in that atom. 1. Oxidizing Agent The electron donor is called the reducing agent , and the electron acceptor is called the oxidizing agent . 1. Oxidizing and reduction always go together!! Doesn’t have to be the complete transfer of electrons from one atom to another. It can involve a change in the level of electron sharing within a covalent bond. In methane (CH 4 ), C and H have similar electronegativites, so the valence electrons are shared equally. But when methane reacts with oxygen carbon dioxide is formed (CO 2 ). 1. Carbon is now bonded to oxygen, which is much more electronegativites then hydrogen so, carbon has partially lost its shared electrons, and has become oxidized (+). Figure 9.3 Electronegativity Pulling an electron away from an atom requires energy. The more electronegative an atom is the more energy is required to take an electron away from it. An electron loses potential energy when it shifts from a less electronegative atom to a more electronegative one (just as a ball loses potential energy once it is rolled down a hill). Cellular Respiration as a redox reaction (figure on Moodle) Glucose is oxidized during cellular respiration.
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The electrons lose potential energy as they are transferred from a less electronegative atom (C) to a more electronegative atom (O), and this energy is released. Hydrogen: Organic molecules that contain a lot of hydrogens make really good fuels. Think saturated hydrocarbons.
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