1. Water— The Elixir of Life!

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

3. Chemistry of water Water is a polar molecule
A hydration shell forms as water surrounds an ion
+ & – poles
Each water molecule can form a maximum of four hydrogen bonds at a time

4. The Chemistry of Water
Unique physical properties include high specific heat Due to its high specific heat, water is slow to undergo changes in temperature. Much heat must be added or removed before the temperature of water changes much. The temperature of the water within living organisms tends to change more slowly than does that of the surrounding air or soil, so that the living cells are buffered somewhat against temperature fluctuations. This kind of protection is important because many biochemical reactions will take place only within a narrow range of temperatures.

5. The Chemistry of Water
Unique physical properties, include a high heat of vaporization. This means that in order for water to reach the gaseous state, it must absorb a great deal of heat from the surroundings.
For many plants and animals, this property is the basis of a natural cooling system. Water evaporating from leaves, skin or lungs uses up heat from the organisms in the process of changing from liquid to gas. That is the reason mammals have evolved sweat glands, when the body is overheated, the glands pour watery "sweat" onto the skin, as the water evaporated, large amounts of body heat are used up and the body is cooled.

6. Water Holds Immense Amounts of Heat
Forecast for San Diego and Gallup
1/11/06-1/15/06
Why does it get so much colder at night in Gallup? See next slide if you can’t figure it out.
Water’s high heat capacity has profound effects on climate and ecology. .

8. Surface Tension H bonding between H2O creates cohesion
water is “sticky”
Tensile strength is related to cohesion and is a measure of the resistance of molecules to being pulled apart. This phenomena is responsible for "surface tension" that you see above. The water strider can "walk on water" because its feet don’t push hard enough to force the water molecules apart.

9. Transpiration
Water has several other properties that make it important to living things. Water molecules exhibit strong cohesion = the tendency of "like" molecules to stick together.
This is the result of the polar nature of water molecules and the resulting hydrogen bonding. In the photos, water is transported up inside trees and other vascular plants inside tiny tubes call "xylem vessels". As water transpires off the leaves the cohesion pulls more water up through the vessels. (remember this when we get to plant form and function)

10. The Chemistry of Water
Water shows strong adhesion : tendency of "unlike" molecules to cling together – capillary action
High surface tension allows long water columns to be drawn from roots to leaves – even in a redwood. (It’s that transpiration thing again!)

11. Water is a wonderful solvent.
Dissolving table salt (sodium chloride)
Solution: a mixture where everything is equally distributed

12. Hydrophilic Hydrophilic substances have affinity for H2O
polar or non-polar?
ionic
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?

13. Hydrophobic Hydrophobic substances do not have affinity for H2O
polar or non-polar?
non-ionic
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?
fat (triglycerol)

14. The special case of ice
Most substances are more dense when they are solid
But not water…
Ice floats!
H bonds form a crystal with loose structure

15. Water Is Lighter as Solid than as a Liquid (so we can go ice fishing)
This means that ice forms an insulating blanket over water.

16. Why is “ice floats” important?
Oceans & lakes don’t freeze solid
if ice sank…
eventually all ponds, lakes & even ocean would freeze solid
during summer, only upper few inches would thaw
surface ice insulates water below
allowing life to survive the winter
seasonal turnover of lakes
cycling of nutrients

17. Water forms ions
Hydrogen ion (H+) splits off from water to leave a hydroxide ion (-OH)
H > H OH
Low pH = lots of H+s = Acid
High pH = few H+s = Base
pH scale = how acidic or basic a solution is
a measure of proton concentration H+
In biology, keeping H+ levels within a narrow range is critically important.
Most biological fluids have pH 6 – 8
pH values in human stomach can reach 2

18. pH Scale [H+] [OH-] = 10-14 Water is neutral!!! pH = 7
In pure water only 1 water molecule in every 554 million is dissociated.
very small amount of ions
[H+] or [OH-] is 10-7M
[H+] [OH-] = 10-14
pH scale is based on this equation
Buffers are substances that minimize changes in pH. They accept H+ from solution when they are in excess and donate H+ when they are depleted.
Carbonic acid (H2CO3) is an important buffer in living systems. It moderates pH change in blood plasma and the ocean.
Exercise = acidic in muscles
CO2 = carbonic acid
lactic acid
body uses buffers to counter act this

19. Punchline Water is a polar molecule
The special properties of water make life on Earth possible
The chemical behavior of water governs how organisms function

20. Any Questions??