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Water and the Fitness of the Environment Properties of water (and how they’re important for life) WATER IS POLARPolarity of Water (and the importance of H-bonding)-partially negative oxygen (O-) will bond with partially positive hydrogen (H+) on a different molecule of H2O = this is a HYDROGEN BOND WATER HAS UNIQUE MOLECULAR INTERACTIONS1. cohesion = H-bonding between like molecules (water-water)-surface tension – measure of how difficult it is to break or stretch the surface of a liquid2. adhesion = bonding between unlike molecules (water-something) -adhesion of water to vessel walls counters the downward pull of gravity transpiration = movement of water up plants-water molecules cling to each other because of cohesion and the xylem of the plant by adhesion WATER MODERATES TEMPERATURE-remember, heat = total amount of KE in a system, temperature = measure of the intensity of heat due to average KE of molecules -retention of temperature-water has a high specific heat -changes temp less when absorbs/loses heat-large bodies of water absorb and store more heat (hence warmer coastal areas), stable marine/land environments w/o large fluctuations in temp-evaporative cooling -water has a high heat of vaporization -molecules with greatest KE leave as gas -keeps temps stable (cools plants, sweat in humans)-insulation by ice -less dense, floating ice insulates liquid water below -life exists under frozen surface in aquatic environments WATER IS THE SOLVENT OF LIFE-solution – liquid homogeneous mixture of 2+ substances-solvent – dissolving agent (liquid)-solute – dissolved substance-water is an extremely versatile solvent where “like dissolves like”-hydrophilic – affinity for water, polar substances and ions (cellulose, sugar, salt… blood)-hydrophobic – repels water, nonpolar substances (oils, lipids… cell membranes)Acids and Bases-water can gain protons (hydronium ions) or lose protons (hydroxide ions) -H2O <> H+ + OH- -gain proton: H+ + H2O à H3O+ -lose proton: H2O – H+ à OH- -acids = increase H+ concentration (ex:HCl)-base = reduces H+ concentration (ex:NaOH) -most biological fluids are pH 6-8 ***Calculating pH*** [H+][OH-] = 10-14 if [H+] = 10-6M, then [OH-] = 10-8 pH = -log[H+] if [H+] = 10-2, then –log 10-2 = -(-2) = 2, therefore, pH = 2if [OH-] = 10-10, then [H+] = 10-4, so –log 10-4 = -(-4) = 4, therefore pH = 4 -Buffers = minimize changes in concentration of H+ and OH- in a solution (weak acids and bases)-buffers keep blood at pH~7.4… because if blood if blood drops to 7 or up to 7.8, DEATH.-carbonic acid-bicarbonate system: important buffers in blood plasma H2CO3 (carbonic acid) à HCO3--ocean acidification threatens coral reef ecosystems b/c CO2 mixed with seawater à carbonic acid (lowers ocean pH)-acid precipitation threatens fortes and lake ecosystems SUMMARYCohesion – polar, H-bond, like-like – water defies gravity in plants/treesAdhesion – H-bond, water-unlike – plants/xylem, blood/veinsSurface tension – diffs in stretch, break surface, H-bond – bugs/walk on waterSpecific heat – absorbs/retains E, H-bonds – oceans mod temp, protect marine lifeEvaporation – liquid to gas, KE – cooling homeostasisUniversal substance – polarity, ionic, H-bonds – good dissolver, solvent
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