bio- chap 3 - I. Abundunce of water A. earth began in water...

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I. Abundunce of water A. earth began in water and evolved there for 3 billion years before spreading onto land B. all life tied to water 1. surrounded 2. cells are also 70-95% water C. reason earth is inhabitable II. Effects of Water’s Polarity A. Polarity = hydrogen bonding 1. structure a. two hydrogen atoms are joined to the oxygen atom by single covalent bonds b. oxygen is more electronegative than hydrogen, electrons of the polar bonds spend more time closer to O atom -> O has slight neg charge, H has slight pos charge c. shaped as a V polar molecule means opp ends of the molecule hav opp charges 2. properties a. from attraction between polar molecules b. electrical attraction; pos end to neg end, etc. c. emergent properites resulting from higher level of structural organization (water molecule can form 4 hydrogen bonds to max of 4 neighbors) B. Cohesion: hydrogen bonds hold the substance together 1. water molecules stick together as a result of hydrogen bonding 2. (1/20 as strong as covalent bonds, are fragile) a. form, break, rebreak with great frequency b. only lasts a few trillioninths of a second c. succession of partners continuously 3. Transport of water against gravity in plants a. leaf gets water thru vessels from roots, and water constantly replaced when it evaporates b. hydrogen bonds cause water molecules leaving the veins to tug on molecules farther down in the vessel and upward pull is transmitted along vessel all the way down to the roots c. Adhesion : clinging of one substance to another. Water to walls of vessel d. Surface tension : measure of how difficult it is to stretch /break the surface of a liquid. Water has greater level than most liquids C. Temperature on Earth 1. stabalizes temp or earth by absorbing heat from air that is warmer and releasing stored heat to air that is cooler, but it only encounters a slight
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This note was uploaded on 02/25/2012 for the course BIO 1421 taught by Professor Farr during the Fall '08 term at Texas State.

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bio- chap 3 - I. Abundunce of water A. earth began in water...

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