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Biology Chapter 3 Notes

Biology Chapter 3 Notes - CHAPTER 3 WATER AND THE FITNESS...

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CHAPTER 3 WATER AND THE FITNESS OF THE ENVIRONMENT Water's extraordinary properties are emergent properties resulting from water's structure and molecular interactions. I. Water's Polarity and Its Effects A. The polarity of water molecules results in hydrogen bonding Water is a polar molecule. Its polar bonds and asymmetrical shape give water molecules opposite charges on opposite sides. - Four valence orbitals of O point to corners of a tetrahedron. -Two corners are orbitals with unshared pairs of electrons and weak negative charge. -Two corners are occupied by H atoms which are in polar covalent bonds with O. Oxygen is so electronegative, that a H shared electrons spend more time around the O causing a weak positive charge near H's. Hydrogen bonding orders water into a higher level of structural organization. -The polar molecules of water are held together by hydrogen bonds. -Positively charged H of one molecule is attracted to the negatively charged O of another water molecule. Water has extraordinary properties that emerge as a consequence of its polarity and hydrogen-bonding. Some of these properties are that water: - has cohesive behavior - resists changes in temperature - has a high heat of vaporization and cools surfaces as it evaporates - expands when it freezes - is a versatile solvent B. Organisms depend on the cohesion of water molecules. Cohesion = Phenomenon of a substance being held together by hydrogen bonds. -Though hydrogen bonds are transient, enough water molecules are hydrogen bonded at any given time to give water more structure than other liquids. -Contributes to upward water transport in plants by holding the water column together. Adhesion of water to vessel walls counteracts the downward pull of gravity.
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