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chap9studyguide - Chapter 9 Cellular Respiration Harvesting...

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Chapter 9 Cellular Respiration: Harvesting Chemical Energy Study Guide Overview: Life Is Work To perform their many tasks, living cells require energy from outside sources. Energy enters most ecosystems as sunlight and leaves as heat. Photosynthesis generates oxygen and organic molecules that the mitochondria of eukaryotes use as fuel for cellular respiration. Cells harvest the chemical energy stored in organic molecules and use it to regenerate ATP, the molecule that drives most cellular work. Respiration has three key pathways: glycolysis, the citric acid cycle, and oxidative phosphorylation. Concept 9.1 Catabolic pathways yield energy by oxidizing organic fuels The arrangement of atoms of organic molecules represents potential energy. Enzymes catalyze the systematic degradation of organic molecules that are rich in energy to simpler waste products with less energy. Some of the released energy is used to do work; the rest is dissipated as heat. Catabolic metabolic pathways release the energy stored in complex organic molecules. One type of catabolic process, fermentation, leads to the partial degradation of sugars in the absence of oxygen. A more efficient and widespread catabolic process, cellular respiration, consumes oxygen as a reactant to complete the breakdown of a variety of organic molecules. ° In eukaryotic cells, mitochondria are the site of most of the processes of cellular respiration. Cellular respiration is similar in broad principle to the combustion of gasoline in an automobile engine after oxygen is mixed with hydrocarbon fuel. ° Food is the fuel for respiration. The exhaust is carbon dioxide and water. The overall process is: ° organic compounds + O 2 CO 2 + H 2 O + energy (ATP + heat). Carbohydrates, fats, and proteins can all be used as the fuel, but it is most useful to
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consider glucose. ° C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy (ATP + heat) The catabolism of glucose is exergonic with a G of 686 kcal per mole of glucose. ° Some of this energy is used to produce ATP, which can perform cellular work. Redox reactions release energy when electrons move closer to electronegative atoms. Catabolic pathways transfer the electrons stored in food molecules, releasing energy that is used to synthesize ATP. Reactions that result in the transfer of one or more electrons from one reactant to another are oxidation-reduction reactions, or redox reactions. ° The loss of electrons is called oxidation. ° The addition of electrons is called reduction. The formation of table salt from sodium and chloride is a redox reaction. ° Na + Cl Na + + Cl ° Here sodium is oxidized and chlorine is reduced (its charge drops from 0 to 1). More generally: X e + Y X + Y e ° X, the electron donor, is the reducing agent and reduces Y.
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chap9studyguide - Chapter 9 Cellular Respiration Harvesting...

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