Chapter_3 notes - Chapter 3 - Water Water is necessary for...

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Chapter 3 - Water Water is necessary for life Cells are 70-95% water Water is the only common substance to exist in the natural environment in all three physical states of matter Solid – ice Liquid – water Gas – water vapor (clouds) Hydrogen bonds Oxygen is very electronegative Water molecules have polar covalent bonds H are partially positive and the O is partially negative Results in hydrogen bonds between water molecules 1/20 th the strength of covalent bonds Constantly forming, breaking and reforming with other molecules Each only exists for trillionths of a second At any given point, a substantial portion of water molecules are bonded to their neighbors Hydrogen bonds cause water to have very different properties than most other liquids These unique properties contribute to Earth’s ability to sustain life Four emergent properties of water Cohesive behavior Moderation of temperature Expansion upon freezing Versatility as a solvent 1. Cohesive behavior Hydrogen bonds cause water to be more structured and hold together more than other liquids Cohesion – molecules cling to one another (forming water droplets) Adhesion – clinging of one substance to another (droplets clinging to spider web) 2. Moderation of Temperature Water has a high specific heat, which means that it takes a lot of energy to change the temperature of water Water can absorb or release a large amount of heat with only a slight change in its own temperature As a result, water minimizes temperature fluctuations to within limits that permit life Since organisms are composed primarily of water, they are better able to resist temperature changes as well Celsius – metric temperature scale, used in science Water freezes at 0 o C Water boils at 100 o C Average body temperature 37 o C Average room temperature 20-25 o C
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This note was uploaded on 09/18/2011 for the course BIOL 1301 taught by Professor Harden during the Spring '11 term at Lone Star College.

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Chapter_3 notes - Chapter 3 - Water Water is necessary for...

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