Ch_3_Notes - Chapter 3 8/29 NO CLASS MONDAY!...

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Chapter 3 8/29 NO CLASS MONDAY!
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Water Supports All Life Organisms are composed of mostly water Humans are 70% water Life on earth began in water 3 billion yrs before land You can survive weeks without food, 1 wk without water Why? Water is necessary in chemical reactions necessary to sustain life
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Most cells surrounded by water Cells 70-95% water 75% earth covered in water Water is unique Only substance exists in natural environment in all 3 physical states of matter Solid, liquid, gas
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Structure of Water Structure of water responsible for its unique properties Simple 2 H atoms joined to 1 O by single polar covalent bonds Polar Molecule- opposite ends of the molecule have opposite charges Positive Charge One Water Molecule Negative Charge Positive Charge
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Unique Properties arise from attractions  between polar molecules. Hydrogen bonding (H bond) Liquid- arrangement of molecules constantly changing, many molecules are linked by multiple H bonds
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4 Properties of Water 1. Cohesion 2. Moderation of temperature 3. Expansion upon freezing 4. Versatility as a solvent
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Cohesion Water molecules are attracted to each other due to H bonds- stay very close together Liquid- H bonds constantly breaking and re-forming At any instance a substantial % of all water molecules are bonded together This makes water more structured than other liquids
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Cohesion Contributes to transport of water & dissolved nutrients against gravity in plants Water evaporates from leaves, H bonding causes the water molecules leaving to pull up on the molecules below it Upward pull is transmitted through all the cells all the way down to the roots
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Adhesion Clinging of one substance to another Water adheres to walls of the cells, countering the downward pull of gravity
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Surface Tension Interface between water & air ordered arrangement of water molecules H-bonded to one another & water below Behaves like an invisible film Measure of how difficult it is stretch or break the surface of a liquid Water has a greater surface tension than most liquids
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Moderation of Temperature Moderates air temperature by absorbing heat from air that is warmer and releasing stored heat to air that is cooler Heat Bank- stores heat Can absorb or release a large amount of heat with only a slight change in its own temperature
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Heat and Temperature Kinetic energy- energy of motion Atoms & molecules have kinetic energy- always in motion Faster a molecule moves, more kinetic energy it has Heat- total amount of kinetic energy due to molecular motion in a body of matter Temperature- measures the intensity of heat due to the average kinetic energy of molecules
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Average speed of molecules increase, temperature increases Heat and temperature are related but not the same Heat -total amt of kinetic energy
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This note was uploaded on 12/01/2009 for the course BIOL 1441 taught by Professor Fredrick during the Fall '08 term at UT Arlington.

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Ch_3_Notes - Chapter 3 8/29 NO CLASS MONDAY!...

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