BIOL 101 Chp 3: Water and Life
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BIOL 101 General Biology I
Chapter 3
Water & the Fitness of the Environment
Rob Swatski Associate Professor of Biology
HACC – York Campus 1
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Water: The Molecule That Supports All of Life
• Water is the biological medium on Earth
• All living organisms require water more than any other substance
• Most cells are surrounded by water, and cells themselves are about 70–95% water
• The abundance of water is the main reason the Earth is habitable
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Water = Life
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Surface of Mars Surface of Earth
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Water = Polar molecule
N
S
+
-
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–
H
+
H
O
+
+
+
–
–
– Hydrogen bond
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Properties of Water
How do they benefit living things? 8
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Emergent Properties of Water
Cohesion Moderates
temperature Expands
when frozen Versatile solvent
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Cohesion
How?
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Water-conducting cells
Adhesion
Cohesion
150 µm
Direction of water movement
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Surface Tension
How?
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Moderates Temperature
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Moderation of Temperature by Water
• Water absorbs heat from warmer air and releases stored heat to cooler air
• Water can absorb or release a large amount of heat with only a slight change in its own temperature
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Energy & Water
Potential
Kinetic
Heat
Temperature
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Metric System Units - Energy
Celsius calorie
(cal)
kilocalorie (kcal or Calorie)
joule
1j = 0.239 cal
1 cal = 4.184 j
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Specific Heat
1 cal/g/ºC
So what…?
HEAT +/- 1 g 1ºC
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• 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
• The high specific heat of water minimizes temperature fluctuations to within limits that permit life
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–
H
+
H
O
+
+
+
–
–
– Hydrogen bond
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Heat Heat
What happens to the bond?
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Heat Heat
What happens to the bond?
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Santa Barbara 73°
Los Angeles
(Airport) 75°
Pacific Ocean 68°
Santa Ana 84°
Burbank 90°
San Bernardino 100°
Palm Springs 106°
Riverside 96°
San Diego 72° 40 miles
70s (°F)
80s
90s
100s
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Evaporation
Heat of evaporation
Evaporative cooling
Helps stabilize
temperatures
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Floating of Ice on Liquid Water
• Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less dense
• Water reaches its greatest density at 4°C
• If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth
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Ice and Insulation
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Solute Solvent Solution
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Aqueous solution
Hydration shell
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“Like Dissolves Like”
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Polar Polar
Hydrophilic
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Polar Nonpolar
Hydrophobic
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Colloid
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Solute Concentration in Aqueous Solutions
• Most biochemical reactions occur in water
• Chemical reactions depend on collisions of molecules and therefore on the concentration of solutes in an aqueous solution
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• Molecular mass: the sum of all masses of all atoms in a molecule
• Numbers of molecules are usually measured in moles, where 1 mole (mol) = 6.02 x 1023 molecules
• Avogadro’s number and the unit dalton were defined such that 6.02 x 1023 daltons = 1 g
• Molarity (M): the number of moles of solute per liter of solution
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One Mole =
molecules
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Hydronium ion (H3O+)
Hydroxide ion (OH–)
2H2O
H
H
H
H
H
H
H
H
O O O O
Hydrogen is Shifty
gains H+ loses H, but keeps e-
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Dynamic equilibrium: dissociation rate = reformation rate
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44 anions cations both
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pH Scale
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Acidic [H+] > [OH–]
Neutral [H+] = [OH–]
Basic [H+] < [OH–]
7
0
14
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pH Scale
Battery acid
Gastric juice, lemon juice
Vinegar, wine,
cola
Beer Tomato juice
Black coffee
Rainwater
Urine
Saliva
Pure water
Human blood, tears
Seawater
Inside of small intestine
Milk of magnesia
Household ammonia
Household
bleach
Oven cleaner
Basic solution
Neutral solution
Acidic solution
0
1
2
3
4
5
6
7
8
9
10
Neutral
[H+] = [OH]
Inc
rea
sin
gly
Ba
sic
[H+]
< [
OH]
Inc
rea
sin
gly
Ac
idic
[H+]
> [
OH]
H+ H+
H+
H+ H+
H+
H+
H+
OH
OH
H+
OH
H+
OH OH
OH OH H+
H+ H+
H+
OH OH
OH
OH OH OH
OH H+
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12
13
14
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pH Values
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Buffers
• The internal pH of most living cells must remain close to pH 7
• Buffers are substances that minimize changes in concentrations of H+ and OH– in a solution
• Most buffers consist of an acid-base pair that reversibly combines with H+
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Carbonic Acid
H2CO3
Bicarbonate ion
HCO3-
Carbonic acid-Bicarbonate buffer system
H+
OH+
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Buffering Systems
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How can your commute
affect coral reef growth
in the Caribbean
Sea?
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Acidification: A Threat to Water Quality
• Human activities such as burning fossil fuels threaten water quality
• CO2 is the main product of fossil fuel combustion
• About 25% of human-generated CO2 is absorbed by the oceans
• CO2 dissolved in sea water forms carbonic acid; this process is called ocean acidification
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• As seawater acidifies, H+ ions combine with carbonate ions to produce bicarbonate
• Carbonate is required for calcification (production of calcium carbonate) by many marine organisms, including reef-building corals
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CO2
CO2 + H2O H2CO3
H+ + HCO3
H+ + CO32 HCO3
CaCO3 CO3
2 + Ca2+
H2CO3
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(a) (b) (c)
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• The burning of fossil fuels is also a major source of sulfur oxides and nitrogen oxides
• These compounds react with water in the air to form strong acids that fall in rain or snow
• Acid precipitation is rain, fog, or snow with a pH lower than 5.2
• Acid precipitation damages life in lakes and streams and changes soil chemistry on land
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More acidic
0
Acid rain
Normal rain
More basic
1
2
3
4
5
6
7
8
9
10
11
12
13
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