tailieunhanh - Lecture Biology (6e): Chapter 3 - Campbell, Reece
Chapter 3 - Water and the fitness of the environment. After reading this chapter and attending lecture, the student should be able to: Describe how water contributes to the fitness of the environment to support life; describe the structure and geometry of a water molecule, and explain what properties emerge as a result of this structure; explain the relationship between the polar nature of water and its ability to form hydrogen bonds;. | CHAPTER 3 WATER AND THE FITNESS OF THE ENVIRONMENT Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section A: The Effects of Water’s Polarity 1. The polarity of water molecules results in hydrogen bonding 2. Organisms depend on the cohesion of water molecules 3. Water moderates temperatures on Earth 4. Oceans and lakes don’t freeze solid because ice floats 5. Water is the solvent of life Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Because water is the substance that makes possible life as we know it on Earth, astronomers hope to find evidence of water on newly discovered planets orbiting distant stars. Life on Earth began in water and evolved there for 3 billion years before spreading onto land. Even terrestrial organisms are tied to water. Most cells are surrounded by water and cells are about 70-95% water. Water exists in three possible states: ice, liquid, and vapor. In a water molecule two hydrogen atoms form single polar covalent bonds with an oxygen atom. Because oxygen is more electronegative, the region around oxygen has a partial negative charge. The region near the two hydrogen atoms has a partial positive charge. A water molecule is a polar molecule with opposite ends of the molecule with opposite charges. 1. The polarity of water molecules results in hydrogen bonding Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Water has a variety of unusual properties because of attractions between these polar molecules. The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. Each water molecule can form hydrogen bonds with up to four neighbors. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. The hydrogen bonds joining water molecules are weak, about 1/20th as strong as covalent bonds. They form, break, and reform with great frequency. At any instant, a | CHAPTER 3 WATER AND THE FITNESS OF THE ENVIRONMENT Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section A: The Effects of Water’s Polarity 1. The polarity of water molecules results in hydrogen bonding 2. Organisms depend on the cohesion of water molecules 3. Water moderates temperatures on Earth 4. Oceans and lakes don’t freeze solid because ice floats 5. Water is the solvent of life Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Because water is the substance that makes possible life as we know it on Earth, astronomers hope to find evidence of water on newly discovered planets orbiting distant stars. Life on Earth began in water and evolved there for 3 billion years before spreading onto land. Even terrestrial organisms are tied to water. Most cells are surrounded by water and cells are about 70-95% water. Water exists in three possible states: ice, liquid, and vapor. In a water molecule two hydrogen atoms form .
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