Chapter 9- Cellular Respiration

Chapter 9- Cellular Respiration - 1/26/2010...

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1/26/2010 1 Cellular Respiration © 2010: D. Julian Life requires energy Energy flows into an ecosystem as sunlight and leaves as heat. Photosynthesis generates O 2 and organic molecules, Light energy ECOSYSTEM Photosynthesis in chloroplasts CO 2 + H 2 O Cellular respiration Organic molecules + O 2 which are used in cellular respiration. Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work. © 2010: D. Julian in mitochondria ATP powers most cellular work Heat energy ATP Types of catabolic pathways Catabolic pathways yield energy by oxidizing organic fuels, which is an exergonic process. Fermentation is a partial degradation of sugars that occurs without O 2 . Aerobic respiration consumes organic molecules and O 2 and yields ATP. Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O 2 . © 2010: D. Julian
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1/26/2010 2 The general scheme of catabolism Carbohydrates, fats and proteins are oxidized (“combusted”) in metabolic pathways controlled by enzymes in order to replenish the ATP (i.e., supply the energy) needed by cells/organisms. The general scheme is: Organic compounds + O + ADP +P © 2010: D. Julian Organic compounds + O 2 + ADP +P i CO 2 + H 2 O + Energy (ATP + heat) With glucose being oxidized as the substrate: C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + ATP + heat Redox Reactions © 2010: D. Julian Redox reactions: oxidation and reduction Chemical reactions that transfer electrons between reactants are called oxidation reduction reactions, or redox reactions . In oxidation , a substance loses electrons, or is oxidized. In reduction , a substance gains electrons, or is reduced (the amount of positive charge is reduced). © 2010: D. Julian
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1/26/2010 3 Energy transfer in redox reactions The transfer or relocation of electrons ( e ) through oxidation reduction (redox) reactions releases energy stored in organic molecules. An electron loses energy when it shifts from a less electronegative atom to a more electronegative atom. © 2010: D. Julian becomes oxidized becomes reduced Energy transfer in redox reactions The electron donor is called the reducing agent. The electron receptor is called the oxidizing agent. becomes oxidized © 2010: D. Julian (loses electron) becomes reduced (gains electron) Changes in electron sharing Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds. Reactants becomes oxidized Products © 2010: D. Julian becomes reduced Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water
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1/26/2010 4 Oxidation of organic fuels Fuels such as carbohydrates, fats and proteins are reservoirs of “high energy” (“hilltop”) electrons associated with hydrogen becomes oxidized becomes reduced © 2010: D. Julian associated with hydrogen.
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Chapter 9- Cellular Respiration - 1/26/2010...

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