Chapter 3 Water & Biology
Jan 04, 2016
Chapter 3
Water & Biology
H2O is why we are here
• H2O molecules are polar• What does their polarity contribute to?
• Each H2O molecule can form __ Hydrogen bonds?
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?
Transpiration (Plants)
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
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?
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?
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
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?
Hydrogen Bonding
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)
Remember…
• Hydrophilic = polar molecule• Will dissolve in water
• Hydrophobic = nonpolar molecule• Will NOT dissolve in water
• What about ionic compounds?