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Chapter 14 Answers - Study Guide Chapter 14 Mitochondria...

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1 Study Guide Chapter 14: Mitochondria Answers 14-1 Choices (a), (d) and (e) are correct. Fermentation probably evolved before aerobic respiration because the early earth had a very low concentration of atmospheric oxygen (choice (a)). Fermentation probably evolved before photosynthesis because it is far simpler and more fundamental than photosynthesis or aerobic respiration (thus b is unlikely). Once photosynthetic reactions caused an increase in the concentration of free oxygen, organisms that were able to catalyze reactions of aerobic respiration came to have an enormous selective advantage (choice (e)). Chemiosmotic coupling, which forms the basis of both aerobic respiration and photosynthesis, first evolved in prokaryotes (thus choice (c) is incorrect). It is thought that the ancestor of eucaryotic cells enveloped a bacterial cell capable of aerobic respiration, which then became the mitochondria; a similar mechanism of envelopment and symbiosis that occurred later probably originated the chloroplasts (choice (d)). 14-2 True. When the citric acid cycle is operating as a cycle of reactions, the primary products from a single molecule of pyruvate are 3 CO 2 , 1 GTP, 3 reduced NADH, and 1 reduced FADH 2 . The electrons in NADH and FADH 2 are passed into the electron transport chain to generate ATP via oxidative phosphorylation. Although a single GTP is made directly by the citric acid cycle, many molecules of ATP are made by oxidative phosphorylation of the 3 NADH molecules and 1 FADH 2 . 14-3 True. An electron carrier with low electron affinity carries the electron in a high-energy state. Transfer of an electron from a low-affinity carrier to a high-affinity carrier is energetically favorable. Thus, transfer of an electron to compounds with sequentially
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