1. Water is the biological medium on Earth
Fig. 3-1
Water is the biological medium on Earth
Most cells are surrounded by water, and cells themselves are about 70–95% water
Figure 3.1 Why does the abundance of water allow life to exist on the planet Earth?
The abundance of water is the main reason the Earth is habitable
All living organisms require water more than any other substance

2. Water is a ______ Molecule
Diagram of a Water Molecule

3. The polarity of water allows for hydrogen bonding
Fig.3.2
The polarity of water allows for hydrogen bonding
 –
Hydrogen
bond
 + H —— O
 –
 + —— H
 –
 +
Figure 3.2 Hydrogen bonds between water molecules
 –
 +

4. Unique Properties of Water
How do they facilitate an environment for life?
Cohesive behavior
Ability to moderate temperature
Expansion upon freezing
Versatility as a solvent
Why is this important?

5. Cohesive Behavior Cohesion: attraction of like molecules
ex/___________
Adhesion:
attraction of unlike molecules ex?__________
Why is this important?

6. Adhesion Water-conducting cells Cohesion 150 µm
Fig. 3-3
Adhesion
Water-conducting
cells
Direction
of water
movement
Cohesion
Figure 3.3 Water transport in plants
150 µm

7. Fig. 3-4
Figure 3.4 Walking on water
Why does water have a high surface tension (measure of how hard it is to break the surface of a liquid)?

8. Moderation of Temperature
Water has a high specific heat (1 cal/g/ºC)
- amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC
Water absorbs heat from warmer air and releases stored heat to cooler air (slight change in own temperature)
Why is this important?
How can water’s high specific heat be traced to hydrogen bonding?

9. Heat of vaporization: is the heat a liquid must absorb for 1 g to be converted to gas
Evaporative Cooling: as a liquid evaporates, its remaining surface cools
helps stabilize temperatures in organisms and bodies of water

10. Expansion Upon Freezing Why does ice float?

11. Hydrogen bonds are stable Hydrogen bonds break and re-form
Fig. 3-6
Expansion Upon Freezing Why does ice float?
Hydrogen
bond
Ice
Hydrogen bonds are stable
Liquid water
Hydrogen bonds break and re-form
Figure 3.6 Ice: crystalline structure and floating barrier
Less Dense: Below ____
More Dense: Above ____
Why is this important?

12. Versatility as a Solvent
Solution: is a liquid that is a homogeneous mixture of substances
Solvent: is the dissolving agent of a solution
The solute is the substance that is dissolved
An aqueous solution is one in which water is the solvent

13. – – – – – – – – – – – + + + + + + + + + + Na Na Cl– Cl–
Fig. 3-7 – Na + + + – – + – – Na + – + +
Cl–
Cl– + – – + – + –
Figure 3.7 Table salt dissolving in water –
Hydration Shell

14. 2H2O Hydronium ion (H3O+) Hydroxide ion (OH–)
Fig. 3-UN2 H H O O O H O H H H H H
2H2O
Hydronium
ion (H3O+)
Hydroxide
ion (OH–)

15. The dissociation of water molecules has a great effect on organisms (the chemistry of cell)
Most biological fluids have pH values in the range of 6 to 8
Buffers: substances that minimize changes in concentrations of H+ and OH– in a solution
Teaching the Blood Buffennnnnnnr System using a Demonstration

16. Figure 3.9 The pH scale and pH values of some aqueous solutions1
Battery acid
Gastric juice,
lemon juice 2 H+ H+ H+ H+
OH– 3
Vinegar, beer,
wine, cola
OH– H+ H+
Increasingly Acidic
[H+] > [OH–] H+ H+ 4
Acidic
solution
Tomato juice
Black coffee 5
Rainwater 6
Urine
OH–
Saliva
OH–
Neutral
[H+] = [OH–] H+ H+
OH– 7
Pure water
OH–
OH– H+
Human blood, tears H+ H+ 8
Seawater
Neutral
solution 9
Figure 3.9 The pH scale and pH values of some aqueous solutions 10
Increasingly Basic
[H+] < [OH–]
Milk of magnesia
OH–
OH– 11
OH– H+
OH–
OH–
Household ammonia
OH– H+
OH– 12
Basic
solution
Household
bleach 13
Oven cleaner 14

17. Human activities such as burning fossil fuels threaten water quality
CO2 is released by fossil fuel combustion and contributes to:
A warming of earth called the “greenhouse” effect
Acidification of the oceans; this leads to a decrease in the ability of corals to form calcified reefs