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Chapter 3

Chapter 3. Water & Biology. H 2 O is why we are here. H 2 O molecules are polar What does their polarity contribute to? Each H 2 O molecule can form __ Hydrogen bonds?. Cohesion & Adhesion. Caused by Hydrogen bonding Cohesion – Water-to-water Adhesion – water-to-something other than water

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Chapter 3

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  1. Chapter 3 Water & Biology

  2. H2O is why we are here • H2O molecules are polar • What does their polarity contribute to? • Each H2O molecule can form __ Hydrogen bonds?

  3. Cohesion & Adhesion • Caused by Hydrogen bonding • Cohesion – Water-to-water • Adhesion – water-to-something other than water • When water travels upward in a straw, is that cohesion or adhesion? Why? • Diameter of straw: small or large? Why?

  4. Transpiration (Plants)

  5. Structure & Function in water transport • What structural feature of water enables it to be transported upward? • Hydrogen bonding  Cohesion + Adhesion • What structural feature of plant vessels enables water to be transported upward? • Hydrophilic walls to enable adhesion • Narrow walls to maximize adhesive forces

  6. Surface Tension • Surface Tension – water can stand above the rim of a glass due to hydrogen bonds • Is surface tension a result of cohesion or adhesion? • Why?

  7. Water Moderates Temperature Temperature – measure of average kinetic energy of molecules Water does this because it has a high specific heat  Water can absorb large amounts of heat but change little in temperature  Guess what type of bonding is responsible for high specific heat?

  8. Sea Breeze? (cranberry juice & …) • Day, land heats up faster (low specific heat) • Air over land rises • Onshore breeze • Night, lands cools faster • Hot air rises over water • Offshore breeze

  9. Evaporative Cooling • Water has high specific heat due to? • Responsible for cooling • Heat is released as liquid is vaporized into gas • Highest energy molecules are vaporized first • Vaporization involves the breaking of which bonds?

  10. Hydrogen Bonding

  11. Like dissolves like… • Water is polar so it dissolves polar substances • Also dissolves ionic solids (salts) • Polar substances = hydrophilic • Hydro = water • -philic = to like (Dendrophiliac – one who likes trees) • Water does not dissolve nonpolar substances • NonPolar substances = hydrophobic • Hydro = water • -phobe = to fear (Triskaidekaphobe – one who fears the number 13)

  12. Remember… • Hydrophilic = polar molecule • Will dissolve in water • Hydrophobic = nonpolar molecule • Will NOT dissolve in water • What about ionic compounds?

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