1. Why are we studying water in Biology?
How does the habitat of a polar bear demonstrate the properties of water?
AP Biology

2. Polar Covalent Bonds Atoms differ in their affinity for electrons
Electronegativity
AP Biology

3. Nonpolar vs Polar Covalent Bonds
Nonpolar Covalent Bonds
Affinity for electrons is the same between identical atoms
Electrons are shared equally & bond is nonpolar
Polar Covalent Bonds
For atoms that differ greatly in electronegativity, electrons are not shared equally.
Shared electrons will likely be closer to the atom with greater electronegativity
Molecule is still electrically neutral but regions of partial (δ) negative & positive charges exist
AP Biology

4. Chemistry of water Polar molecule polar covalent bonds δ+ and δ- poles
AP Biology

5. Water molecules form H bonds with each other
δ+ attracted to δ–  
Hydrogen
bond  +
Polar covalent
bonds    +    +    +
Figure 3.2 Hydrogen bonds between water molecules.

6. Properties of Water Properties exist because of the polarity of water
Cohesion
Adhesion
High Specific Heat
High Heat of Vaporization
Lower Density of Ice
Solubility
AP Biology

7. Cohesion Water molecules are attracted to one another
H bonding between water creates cohesion
Individual H bonds are transient & last only 100 billionth of a second
Cumulative effects of large numbers of H bonds are enormous!
Surface tension
AP Biology

8. Adhesion Water molecules form H bonds with other substances
Capillary action
Meniscus
AP Biology

9. How does water get to top of tree?
Transpiration (cohesion and adhesion)
AP Biology

10. Water is the solvent of life
Water is a good solvent due to its polarity
Polar water molecules surrounds + and – ions
Solvents dissolve solutes creating aqueous solutions
Hydration shell
Sphere of water molecules around each dissolved ion
Nonionic compounds are also water soluble if they have ionic and/or polar regions on their surface
AP Biology

11. Hydrophilic Hydrophilic Substances have affinity for water
Polar or nonpolar?
ionic
(a) Lysozyme molecule in a
nonaqueous environment
(b) Lysozyme molecule (purple) in an aqueous
environment
(c) Ionic and polar regions
on the protein’s surface
attract water molecules.
AP Biology

12. Hydrophobic Substances do not have affinity for water
Polar or nonpolar?
Non-ionic
AP Biology

13. The special case of ice
Most substances are more dense when they are solid
But not water…
Ice floats
H bonds form a crystal with
loose structure
AP Biology

14. Ice floats Liquid water: Hydrogen bonds break and re-form Ice:
Fig. 3-6a
Ice floats
Liquid water:
Hydrogen bonds
break and re-form
Ice:
Hydrogen bonds
are stable
AP Biology

15. Why is the density of ice important?
Oceans and lakes don’t freeze solid
If ice sank…
All ponds, lakes and oceans would eventually freeze solid
During summer, only upper few inches would thaw
Surface ice insulates water below
Allows life to survive winter
Seasonal turnover of lakes
Cycling nutrients
AP Biology

16. AP Biology

17. Specific heat
Amount of heat 1g of a substance must absorb or lose to change its temperature by 1°C
Water has high specific heat
Due to H bonding
Water resists changes in temperature
Takes a lot to heat it up
Takes a lot to cool it down
Water moderates temperatures on earth
AP Biology

18. High Specific Heat
Water will change its temperature less when it absorbs or loses a given amount of heat
In order to change water from solid to a liquid or liquid to a gas:
Hydrogen bonds between water molecules must be broken--heat must be absorbed
AFTER hydrogen bonds are broken, then water molecules can begin to move faster, thus increasing their kinetic energy
The reverse is also true….
AP Biology

19. Heating curve for 1.00 mol of ice at -25° C
AP Biology

20. High Heat of Vaporization
Amount of energy required to change 1g of substance from liquid to gas
Requires lots of heat energy (586 cal) to accomplish this change in water
Facilitates Cooling
Organisms rely on heat of vaporization to remove heat
Evaporative cooling
Results from high heat of vaporization
Tendency for water molecules to move fast enough to overcome attraction to one another and depart the liquid and enter the air as gas
Molecules with greatest energy tend to vaporize first
Reduces average speed of remaining molecules of water
When substance evaporates, surface of liquid remaining behind cools
Cools land dwelling animals and plants, cools bodies of water etc…
AP Biology

21. Why is this important to living things?
Large bodies of water absorb and store huge amount of heat in daytime and during warm seasons, without a dramatic increase in temperature
At night and during cooler seasons, gradual cooling of water warms the air
Results in coastal areas having milder climates than areas further away from the ocean
Tends to stabilize ocean temperatures
Because organisms are made mostly of water, they are able to resist changes in their own temperatures
AP Biology

22. San Bernardino Burbank Santa Barbara 73° 100° 90° Riverside 96°
Fig. 3-5
San Bernardino
100°
Burbank
90°
Santa Barbara 73°
Riverside 96°
Los Angeles
(Airport) 75°
Santa Ana
84°
Palm Springs
106°
70s (°F)
80s
Pacific Ocean
90s
100s
San Diego 72°
40 miles
AP Biology

23. Water forms ions
Hydrogen ion (H+) splits off from water to leave a hydroxide ion (OH-)
If concentration of 2 ions is equal, water is neutral
If [H+] > [OH-], water is acidic
If [OH-] > [H+], water is basic
pH scale
Acidity or basicity of a solution
Relative concentrations of H+ and OH+
AP Biology

24. Acidic [H+] > [OH] Neutral [H+] = [OH] Basic [H+] < [OH]
Figure 3.UN05
Acidic
[H+] > [OH]
Acids donate H+ in
aqueous solutions.
Neutral
[H+] = [OH] 7
Bases donate OH
or accept H+ in
aqueous solutions
Figure 3.UN05 Summary figure, Concept 3.3
Basic
[H+] < [OH] 14 24

25. pH scale
In pure water, only 1 water molecule in every 554 million is dissociated
Very small amount of ions
pH = -log [H+]
[H+] or [OH-] is 10-7 M
pH scale based on this equation
AP Biology

26. pH and biology Most biological fluids pH 6-8
pH values in human stomach can reach 2
Each pH unit represents a 10 fold difference in H+ & OH- concentrations
Small change in pH actually indicates a substantial change in [H+] and [OH-]
AP Biology

27. Buffers Living organisms must maintain pH within a fairly narrow range
Substance that minimizes changes in [H+] & [OH-] in a solution
Buffers accept H+ when they are in excess & donate H+ when they are depleted
AP Biology

28. Acid Deposition More acidic 1 2 3 Acid rain Acid rain 4 5 Normal rain
Fig. 3-10
Acid Deposition
More
acidic 1 2 3
Acid
rain
Acid
rain 4 5
Normal
rain 6 7 8 9 10 11 12 13
More
basic 14
AP Biology

29. Ocean Acidification Carbonic Acid Bicarbonate ion
CO2
Ocean Acidification
Carbonic Acid
CO2 + H2O
H2CO3
H2CO3
H+ + HCO3
Bicarbonate ion
H+ + CO32
HCO3
Reduced amounts of CO32- available for calcification
Figure 3.11 Atmospheric CO2 from human activities and its fate in the ocean.
CO32 +
Ca2+
CaCO3 29

30. Data Analysis 40 (mmol CaCO3/m2 • day) Calcification rate 20 200 250
Figure 3.UN06
Data Analysis 40
(mmol CaCO3/m2 • day)
Calcification rate 20
Figure 3.UN06
200
250
[CO32] (mol/kg)
Researchers measured rate of calcification by reef organisms and examined how calcification rate changed with differing amounts of dissolved carbonate ions in seawater 30