My_Ch3_lecture(2009030423450723) - Chapter 3: Properties of...

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Chapter 3: Properties of Water Purpose : to understand the properties of water (the reasons why water is necessary and makes it possible for life on Earth), pH, and the role of buffers. What you MUST know from Ch 3: Properties of water pH Buffers Water is necessary for life. “Goldilocks Hypothesis” for water is that planets need liquid H 2 O to support life (distance from sun): Venus is too hot. Water is in vaporized form, thick atmosphere traps too much heat, and no liquid oceans to complete the water cycle. Mars is too cold. Water is frozen, no plate tectonics to complete C cycle, and no atmospheric “blanket” to trap heat. Earth is just right . Liquid H 2 O , complete C and water cycles, so atmosphere is the ideal thickness for maintaining an ideal temp. Water’s unique properties are due to its molecular structure and interactions. Water molecules are polar , with a - end (O) and a + end (H), and are held together by (weak) Hydrogen bonds. o Cohesion (tendency of water molecules to stick together) helps plants to pull water up from roots to leaves, as does: o Adhesion (one substance clings to another) keeps water from falling downward due to gravity
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o Surface tension (difficulty breaking the surface of a liquid) is due to the collective strength of water’s hydrogen bonds Water moderates temperature o Water has a very high specific heat (amount of heat that must be absorbed/lost for 1 gram of water to change its temp by 1°C = 1cal/g/°C), due to its Hydrogen bonding Water can absorb or lose a lot of heat without changing its temp This is the reason for the moderating effect of the ocean on earth’s temps (making terrestrial life possible), as well as the stability of the ocean temperature (making marine life possible). Most organisms have a narrow range of temps that they can tolerate. Being composed of a high % of water allows
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This note was uploaded on 09/29/2011 for the course BIO 020.152 taught by Professor Pearlman during the Fall '08 term at Johns Hopkins.

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My_Ch3_lecture(2009030423450723) - Chapter 3: Properties of...

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