1. Ch 3: Water and Life Water and Life Big Idea 2 Essential Knowledge:
2.A.3 Organisms must exchange matter with the environment to grow, reproduce, and maintain organization
Water and Life

3. Why are we studying water?
All life occurs in water
inside & outside the cell

4. Bonds in Biology Weak bonds Strong bonds ionic hydrogen bonds
attraction between + and –
hydrophobic & hydrophilic interactions
interactions with H2O
van derWaals forces
Strong bonds
covalent bonds
sharing electrons
H2O
Hydrogen bond
H2O –
H2 (hydrogen gas)
Covalent bond

5. Chemistry of water H2O molecules form H-bonds with each other
+H attracted to –O
creates a “sticky” molecule
APBio/TOPICS/Biochemistry/Movies AP/hydrogenbonds-Thinkwell.swf

6.   Hydrogen bond  + Polar covalent bonds    +    +    +
Figure 3.2  
Hydrogen
bond  +
Polar covalent
bonds    +    +    +
Figure 3.2 Hydrogen bonds between water molecules. 6

8. Special properties of water
1. cohesion & adhesion
surface tension, capillary action
2. good solvent
many molecules dissolve in H2O
hydrophilic vs. hydrophobic
3. lower density as a solid
ice floats!
4. high specific heat
water stores heat
5. high heat of vaporization
heats & cools slowly
Can we chat more
about this?

9. 1. Cohesion & Adhesion Cohesion Adhesion
H bonding between H2O molecules
water is “sticky”
surface tension
drinking straw
Adhesion
H bonding between H2O & other substances
meniscus
capillary action
water climbs up paper towel or cloth
Cohesion
H bonding between H2O molecules
water is “sticky”
surface tension
capillary action
drinking straw
Adhesion
H bonding between H2O & other substances
meniscus
water climbs up paper towel or cloth

10. Surface Tension
Surface tension is a measure of how hard it is to break the surface of a liquid
Surface tension is related to cohesion
Cohesion
H bonding between H2O molecules
water is “sticky”
surface tension
capillary action
drinking straw
Adhesion
H bonding between H2O & other substances
meniscus
water climbs up paper towel or cloth

11. How does H2O get to top of trees?
Transpiration is built on cohesion & adhesion
APBio/TOPICS/04Biochemistry/MoviesAP/03_03WaterTransport_A.swf

12. 2. Water is the solvent of life (universal solvent)
Polarity makes H2O a good solvent
polar H2O molecules surround + & – ions
solvents dissolve solutes creating solutions
2. Water is a good solvent = the solvent of life
Polarity makes H2O a good solvent
polar H2O molecules surround + & – ions
solvents dissolve solutes creating solutions
What dissolves in water easily?
polar or non-polar molecules?
How about oxygen -- does that dissolve in H2O?

13. What dissolves in water?
Hydrophilic
substances have attraction to H2O
polar or non-polar?
Hydrophilic
substances have attraction to H2O

14. What doesn’t dissolve in water?
Hydrophobic
substances that don’t have an attraction to H2O
polar or non-polar?
Oh, look hydrocarbons!
Hydrophobic
substances that don’t have an attraction to H2O
fat (triglycerol)

15. 3. The special case of ice
Most (all?) substances are more dense when they are solid, but not water…
Ice floats!
H bonds form a crystal
Most (all?) substances are more dense when they are solid, but not water…
Lower density as a solid = Ice floats!
H bonds form a crystal

16. Why is “ice floats” important?
Oceans & lakes don’t freeze solid
surface ice insulates water below
allowing life to survive the winter
if ice sank…
ponds, lakes & even oceans would freeze solid
in summer, only upper few inches would thaw
seasonal turnover of lakes
sinking cold H2O cycles nutrients in autumn
Oceans & lakes don’t freeze solid
surface ice insulates water below
allowing life to survive the winter
if ice sank…
ponds, lakes & even oceans would freeze solid
in summer, only upper few inches would thaw
seasonal turnover of lakes
sinking cold H2O cycles nutrients in autumn

17. 4. Water’s High Specific Heat
The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC
The specific heat of water is 1 cal/g/ºC
Water resists changing its temperature because of its high specific heat
Water’s high specific heat can be traced to hydrogen bonding
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form

18. Specific heat H2O resists changes in temperature high specific heat
takes a lot to heat it up
takes a lot to cool it down
H2O moderates temperatures on Earth (The high specific heat of water minimizes temperature fluctuations to within limits that permit life)
Specific heat
H2O resists changes in temperature
high specific heat = heats & cools slowly
takes a lot to heat it up
takes a lot to cool it down
H2O moderates temperatures on Earth

19. Difference between heat and temperature?
Kinetic energy is the energy of motion
Heat is a measure of the total amount of kinetic energy due to molecular motion
Temperature measures the intensity of heat due to the average kinetic energy of molecules

20. The Celsius scale is a measure of temperature using Celsius degrees (°C)
A calorie (cal) is the amount of heat required to raise the temperature of 1 g of water by 1°C
The “calories” on food packages are actually kilocalories (kcal), where 1 kcal = 1,000 cal
The joule (J) is another unit of energy where 1 J = cal, or 1 cal = J

21. 5. Evaporative Cooling
Evaporation is transformation of a substance from liquid to gas
Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to gas
As a liquid evaporates, its remaining surface cools, a process called evaporative cooling
Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water

22. Organisms rely on heat of vaporization to remove body heat
Evaporative cooling
Organisms rely on heat of vaporization to remove body heat

23. 6. Ionization of water & pH
Water ionizes
H+ splits off from H2O, leaving OH–
if [H+] = [-OH], is neutral
if [H+] > [-OH], is acidic
if [H+] < [-OH], is basic
pH scale
how acidic or basic solution is
1  7  14
Water ionizes
H+ splits off from H2O, leaving OH–
H2O  H+ + OH–
if [H+] = [-OH], water is neutral
if [H+] > [-OH], water is acidic
if [H+] < [-OH], water is basic
pH scale
how acid or basic solution is
1  7  14
H2O  H+ + OH–

24. tenfold change in H+ ions
pH Scale
10–1
H+ Ion
Concentration
Examples of Solutions
Stomach acid, Lemon juice 1 pH
100
Hydrochloric acid
10–2 2
10–3
Vinegar, cola, beer 3
10–4
Tomatoes 4
10–5
Black coffee, Rainwater 5
10–6
Urine, Saliva 6
10–7
Pure water, Blood 7
10–8
Seawater 8
10–9
Baking soda 9
10–10
Great Salt Lake 10
10–11
Household ammonia 11
10–12
Household bleach 12
10–13
Oven cleaner 13
10–14
Sodium hydroxide 14
tenfold change in H+ ions
pH1  pH2
10-1  10-2
10 times less H+
pH8  pH7
10-8  10-7
10 times more H+
pH10  pH8
10-10  10-8
100 times more H+
In pure water only 1 water molecule in every 554 million is dissociated
tenfold change in H+ ions
pH1  pH2
10-1  10-2
10 times less H+
pH8  pH7
10-8  10-7
10 times more H+
pH10  pH8
10-10  10-8
100 times more H+

25. Buffers & cellular regulation
pH of cells must be kept ~7
pH affects shape of molecules
shape of molecules affect function
(therefore, pH affects cellular function)
Control pH by buffers
reservoir of H+
donate H+ when [H+] falls
absorb H+ when [H+] rises 1 2 3 4 5 6 7 8 9
Amount of base added
Buffering
range pH
Exercise = acidic in muscles
CO2 = carbonic acid
lactic acid
body uses buffers to counter act this

26. Do one brave thing today…then run like hell!
Ready for a Lab??
Any Questions?
Do one brave thing today…then run like hell!