AP Biology
Ch 3 - Water
3.1 The Polarity of Water Molecules
Results in Hydrogen Bonding
• H2O – 2 hydrogen, 1 oxygen
• Difference in electronegativity
results in polar bonds
• Asymmetric shape of molecule
results in polar molecule
Directions: Cut out your water molecules. Shade the
positive side red and the negative side black
3.1 The Polarity of Water Molecules
Results in Hydrogen Bonding
• Interactions between
the positive and
negative ends of the
molecules are called
hydrogen bonds
• Molecules of water are
constantly moving,
hydrogen bonds
• 4 emergent properties of water
constantly forming and
result from hydrogen bonding
breaking
3.2 Four Emergent Properties of Water
Property 1: Cohesion
Explain:
Cohesion
– Cohesion
– Adhesion
– Surface tension
Importance in Biology (examples):
Adhesion
3.2 Four Emergent Properties of Water
Property 1: Cohesion
Explain:
• Cohesion – molecules bond to
each other
• Adhesion – Molecules bond
to another substance
• Surface tension – how
difficult it is to break the
surface of a liquid
Importance in Biology:
• Water pulled up tree through transpiration (cohesion)
• Water held inside plants (adhesion)
3.2 Four Emergent Properties of Water
Property 2: Moderation of Temperature
Explain:
–
–
–
–
Kinetic energy
Heat vs temperature
Specific heat
Water as a heat sink
Importance in Biology:
Water molecules being heated
(why does water have a
high specific heat?)
3.2 Four Emergent Properties of Water
Property 2: Moderation of Temperature
• Kinetic energy – energy of motion
• Heat – total kinetic energy
• Temperature - average kinetic energy
y
– Example: Swimmer has higher temp,
pool has higher heat
• Specific heat – amount of heat absorbed to raise temp
of 1 g by 10C
• Water has such a high specific heat because so much
energy goes into breaking the hydrogen bonds
3.2 Four Emergent Properties of Water
Property 2:
Moderation of
Temperature
Importance in Biology:
• Large bodies of water –
cool during the day,
warm at night
• Stable ocean temps
• Regulate the temp of
• Organism’s bodies made of
everything around them –
water – prevents extreme
prevent extreme
fluctuations
fluctuations
3.2 Four Emergent Properties of Water
Property 3: Insulation by Ice
Explain:
Water as a liquid
– water density as liquid vs solid
– Hydrogen bonding as a liquid
vs a solid
Importance in Biology:
Water as solid
3.2 Four Emergent Properties of Water
Property 3: Insulation by Ice
• Water is one of a few substances that is less dense as a solid
• As molecules slow down and get closer together, hydrogen bonding
results in crystalline lattice
Importance in Biology:
• Cold bodies of water freeze over top, not from the bottom up
• Insulates water below, protecting life
3.2 Four Emergent Properties of Water
Property 4: Solvent of Life
Explain:
–
–
–
–
–
solvent, solute
Aqueous solution
Hydration shell
What will dissolve in water?
Hydrophobic vs hydrophilic
Importance in Biology:
Hydration shell
Property 4: Solvent of Life
Explain:
– solvent, solute - Solute
dissolves in solvent
– Aqueous solution – water
is the solvent
– Hydration shell – water
molecules surround solute
particles because of
charges and separate them
– What will dissolve in
water? – Ionic compounds,
polar molecules
– Hydrophobic (affinity for
water) vs hydrophilic (repel
water)
3.2 Four Emergent Properties of Water
Property 4:
Solvent of Life
Importance in Biology:
• Allows chemical
reactions that sustain
life!
• Membranes composed of hydrophobic molecules
allow internal environment to be different than
external environment