1. Properties of Water and the Fitness of the Environment

3. Water Facts
Three-quarters of the Earth’s surface is submerged in water
The abundance of water is the main reason the Earth is habitable
Figure 3.1

4. 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

5. Water Facts 1. water is a polar molecule
2. Polar – when the charge of a molecule is neutral, but uneven
One side is negative, the other is positive O- H+ H+

6. Water Facts
The polarity of water molecules results in hydrogen bonding
3. H bonds – when the negative side of H2O bonds to positive side of another H2O

7. Water Facts
Hydrogen bonds + H
 –
Figure 3.2 + - O- + O- H+

8. Hydrogen Bonds
Why would water’s ability to bond to itself be important for living organisms? (Think of plants especially)

9. Hydrogen Bonds
Capillary action – in plants, hydrogen bonds allow water to move up a stem against gravity

10. Properties of water
7 emergent properties of water contribute to Earth’s fitness for life
Cohesion
Adhesion
Surface tension
Temperature Moderation
High specific heat
Evaporative cooling
Universal solvent

11. Cohesion
Cohesion - the bonding of water molecules to other water molecules
due to
hydrogen bonding

12. Adhesion
2. Adhesion - the bonding of water molecules to non-water molecules

13. Surface Tension
3. Surface tension - hydrogen bond “barrier” made on the surface of water
Why does it happen?
Figure 3.4

14. Moderation of Temperature
4. Water moderates air temperature
a. absorbs heat from warm air and releases stored heat to cool air

15. Water’s High Specific Heat
5. specific heat capacity - the amount of heat that can be absorbed by a substance without raising its temperature

16. Specific Heat a. Water has a high specific heat
allows it to minimize temperature fluctuations to within limits that permit life
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form

17. Specific Heat

18. Evaporative Cooling
6. Evaporative cooling - When water evaporates, it cools the surface it was on
ex) Sweating cools the body

19. Insulation of Bodies of Water by Floating Ice
Solid water, or ice
Is less dense than liquid water
Floats in liquid water
Insulates water & organisms below ice layer

20. Insulation of Bodies of Water by Floating Ice
Since ice floats in water
Life can exist under the frozen surfaces of lakes and polar seas

21. The Solvent of Life
7. Because it is polar, water is a versatile solvent
Other polar things dissolve in water
Called the universal solvent because so many substances dissolve in water

22. Water can also interact with polar molecules such as proteins
This oxygen is attracted to a slight positive charge on the lysozyme molecule.
This oxygen is attracted to a slight negative charge on the lysozyme molecule.
(a) Lysozyme molecule in a nonaqueous environment
(b) Lysozyme molecule (purple) in an aqueous environment such as tears or saliva
(c) Ionic and polar regions on the protein’s Surface attract water molecules. + –
Figure 3.7

23. Hydrophilic and Hydrophobic Substances
hydrophobic substance - no affinity for water
Ex) Nonpolar substances and lipids

24. Hydrophilic and Hydrophobic Substances
2. hydrophilic substance has affinity for water
Ex) Polar or ionic, like carbohydrates and salts

25. Solute Concentration in Aqueous Solutions
Since most biochemical reactions occur in water inside cells (aqueous environments)
It is important to learn to calculate the concentration of solutes in an aqueous solution

26. 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

27. 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

28. Effects of Changes in pH
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
Hydronium
ion (H3O+)
Hydroxide
ion (OH–) + –
Figure on p. 53 of water dissociating

29. 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 (more OH- ions)

30. 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

31. The pH scale and pH values of various aqueous solutions
Increasingly Acidic
[H+] > [OH–]
Increasingly Basic
[H+] < [OH–]
Neutral
[H+] = [OH–]
Oven cleaner 1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH Scale
Battery acid
Digestive (stomach)
juice, lemon juice
Vinegar, beer, wine,
cola
Tomato juice
Black coffee Rainwater
Urine
Pure water
Human blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
Figure 3.8

32. Buffers The internal pH of most living cells Buffers
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

33. The Threat of Acid Precipitation
Refers to rain, snow, or fog with a pH lower than pH 5.6
Is caused primarily by the mixing of different pollutants with water in the air

34. Can damage life in Earth’s ecosystems
Acid precipitation
Can damage life in Earth’s ecosystems 1 2 3 4 5 6 7 8 9 10 11 12 13 14
More acidic
Acid rain
Normal rain
More basic
Figure 3.9