1. Chapter 3 Water and the Fitness of the Environment
Why is water special?
Unique Properties of Water
Acidic/Basic conditions

2. Abundance of water is the main reason the Earth is habitable
Earth’s surface – 75% submerged in water

3. Why is water special? Molecule that supports all life
Biological Medium
Metabolic Reactions
Required for survival of all living organisms
Exists in nature in all 3 states

4. Water Structure Polar molecule Dipole H bonds Contributes to
unique properties

5. What’s wrong with this picture?

6. Unique Properties of Water
Ice floats
a. Less dense
than liquid
water
b. H bonds more ordered and stable in solid water

7. Since Ice floats in water
Life can exist
under the frozen surfaces of lakes
and polar seas

8. Unique Properties of Water
Water has high specific heat
Moderates air temp
1. When air is warmer
2. When air is cooler

9. Review terms
1. Kinetic energy
2. Heat
3. Temperature

10. Review terms
4. specific heat of a substance

11. Unique Properties of Water
Water’s high specific heat
a. Resists change
b. Large bodies of water can absorb heat w/o large temp change
c. Heat absorbed when H bonds break
Heat released when H bonds form

12. d. Bio sig
Water keeps temp fluctuations to within limits that permit life
Due to H bonding, water molecules hold tightly to each other
Aids in homeostasis

13. Unique Properties of Water
High heat of vaporization
a. Vaporization (evaporation)
b. Heat of vaporization

14. Bio sig Evaporative Cooling Due to high heat of vaporization
Allows water to cool a surface
ex.

15. Unique Properties of Water
Cohesion
As a liquid, water forms FRAGILE H bonds
H bonds are constantly breaking and reforming
Definition of cohesion

16. Bio sig
Transport of water and dissolved nutrients against gravity

17. Pond Walkers Bio sig 1. Surface Tension
2. Skin of tightly H bonded water molecules, interface

18. Unique Properties of Life
The Solvent of Life
a. Terms
1. Solution
2. Solvent
3. Solute
4. Aqueous Solution

19. Water is versatile solvent
Hydrophilic
Hydrophobic
Why?
Polarity
Two impt features
1. shape
2. H bonds

20. Water has ability to dissolve macromolecules
Can form sphere of hydration
ex. Fig 3-7 Lysozyme molecule

21. Hydration shell
Polar water can interact with ionic compounds
called solutes and
dissolve them

22. Most biochem rxns occur in water
To calculate concentration of solutes in aqueous solutions:
1. Mole
2. Molarity

23. Unique Properties of Water
Water and pH
a. Dissociation of water molecules affect living organisms

24. Acid/Base
1. Acid
2. Base

25. pH
1. determined by relative conc of H+ ions
2. Definition
pH =

26. pH scale
1. acidic
2. basic

27. Bio sig
1. Homeostasis
all living orgs have a vary narrow pH range over which they can survive.
2. Organisms maintain pH by using

28. Buffers
a. Substances that minimize changes in the concentrations of H+ and OH- ions in a solution
b. Buffer systems are reversible – depends of H+ concentration

29. Buffers consist of: Weak acid and its anionic salt
Weak acid dissociates in aq. Solution
Anionic salt is the negative ion

30. Buffer example - Carbonic Acid
CO2 + H20

31. Clarification

32. Acid Precipitation Rain, snow, or fog with a pH lower than 5.6
Caused by
pollutants
mixing with water
in the air