1
Water and the Fitness of
the Environment
2
Importance of water
• Overview: The Molecule That Supports All of Life
• Water is the biological medium here on Earth
• All living organisms require water more than any other substance
3
Water Facts
• The polarity of water molecules results in hydrogen bonding
• The water molecule is a polar molecule
4
Water’s Polarity• The polarity of water molecules
– Allows them to form hydrogen bonds with each other
– Contributes to the various properties water exhibits
Hydrogenbonds
+
+
H
H+
+
–
–
– –
Figure 3.2
5
Properties of water
• Four emergent properties of water contribute to Earth’s
fitness for life
1. Cohesion - Like molecules bonding to each other (water
attracting other water molecules)
Water conducting
cells
2. Surface tensionIs a measure of how hard it is to break the
surface of a liquid
3. Water moderates air temperature because it has a high specific heat, which allows
it to minimize temperature fluctuations to within limits that
permit life
4. Water is a versatile solvent due to its polarity
6
Insulation of Bodies of Water by Floating Ice
• Solid water, or ice– Is less dense than liquid water– Floats in liquid water
Life can exist under the frozen surfaces of lakes and polar seas
7
• The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve themNegative
oxygen regions
of polar water
molecules are
attracted to sodium
cations (Na+).
+
+
+
+Cl –
–
–
–
–
Na+Positive hydrogen regions
of water molecules cling to chloride anions
(Cl–).
++
+
+
–
–
–
–
–
–Na+
Cl–
Figure 3.6
8
Hydrophilic and Hydrophobic Substances
• A hydrophobic substance– Does not have an affinity for water
• A hydrophilic substance– Has an affinity for water
9
Acids and Bases
• Dissociation of water molecules leads to acidic and basic conditions that affect living organisms
• Organisms must maintain homeostasis in the pH of their internal and external environments
10
• Water can dissociate Into hydronium ions (H+ or H3O+) and hydroxide (OH-) ions
• Changes in the concentration of these ions Can have a great affect on pH in living organisms
H
Hydroniumion (H3O+)
H
Hydroxideion (OH–)
H
H
H
H
H
H
+ –
+
Figure on p. 53 of water dissociating
Effects of Changes in pH
11
Acids and Bases
• An acid– Is any substance that increases the
hydrogen ion concentration of a solution• A base
– Is any substance that reduces the hydrogen ion concentration of a solution
12
The pH Scale• Scale goes from 0-14 with 7 neutral• The pH of a solution Is determined by the
relative concentration of hydrogen ions
• Difference of 10X in hydrogen ion concentration between any two pH values
• Acids have a higher number of H+ ions than a base
• Acids produce H+ ion in solution• Bases produce OH- ions in solution
13
The pH scale and pH values of various aqueous solutions
Incr
easi
ngly
Aci
dic
[H+]
> [
OH
–]
Incr
easi
ngly
Bas
ic[H
+]
< [
OH
–]
Neutral[H+] = [OH–]
Oven cleaner
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
pH Scale
Battery acid
Digestive (stomach) juice, lemon juiceVinegar, beer, wine,colaTomato juice
Black coffee RainwaterUrine
Pure waterHuman blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
Figure 3.8
14
Buffers
• The internal pH of most living cells– Must remain close to pH 7
• Buffers– Are substances that minimize changes
in the concentrations of hydrogen and hydroxide ions in a solution
– Consist of an acid-base pair that reversibly combines with hydrogen ions
– Made by organisms
15
• Acid precipitation– Can damage life in Earth’s ecosystems
0
12
34
56
78
910
11
12
1314
Moreacidic
Acidrain
Normalrain
Morebasic
Figure 3.9
16
Moles and Molarity
• A mole– Represents an exact number of
molecules of a substance in a given mass
• Molarity– Is the number of moles of solute per liter
of solution
17
1 In the beginning God created the heavens and the earth. 2 Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.
God created water before life