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?