1. Water: The Medium of Life

2. Thermal, cohesive and solvent properties of water.
Cohesive Properties – water has a very high cohesion as you learned in chemistry.
Thermal – water has an extremely high specific heat (1 cal/gram or Joules/g). Compare with gold at J/g.
Polarity of water molecule causes it to dissolve other polar substances readily.

3. The properties of water can be explained by the theory that hydrogen bonds form between the molecules.
Water is a polar molecule and hydrogen bonds form between different molecules.

4. The structure of water molecules showing polarity and hydrogen bond formation.
A type of dipole force that occurs between molecules with a Hydrogen and a highly electronegative atom with at least one pair of electrons (F, O, N) (why H2O is liquid at room temp.)
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5. Hydrogen Bond and the structure of Ice.
Note that hydrogen bonds are intermolecular attractions and not true chemical bonds.
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6. Cohesion of water – this allows other objects to be supported:
Okay, so maybe that was a hoax, but this one isn’t:
Cohesion of water allows water to move together up through xylem tubes in plants to the leaves for photosynthesis.

7. Thermal properties of water…
The specific heat, melting point, and boiling point of water are all extremely high.

8. Contrast with Methane
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9. Comparison of the Thermal Properties of Water and Methane
Melting Point
0.0 ºC ºC
Boiling Point
100.0 ºC ºC
Specific Heat
4.184 J g-1 ºC−1
2.20 J g-1 ºC−1
Polarity
Polar
Non-Polar
The Difference is because of Hydrogen bonding!

10. Water is important for the maintenance of homeostasis
The human body is about 70 % water.
Water is used to maintain homeostasis. If the balance is lost, the risk of heat stroke, frostbite, hypothermia, etc. is greatly increased.
Similarly, it takes energy to evaporate water, so sweating cools you down as energy is expended to remove the water.

11. Hydrophobic vs. Hydrophilic
Hydrophobic – literally afraid of water
Hydrophilic – literally loves water

12. Water dissolves many substances.
For this reason, it is an essential medium for transport and metabolism in organisms.

13. Application: Modes of transport of glucose, amino acids, cholesterol, fats, oxygen and sodium chloride in blood in relation to their solubility in water.
Amino acids have positive and negative regions of charge and are soluble in water – carried in plasma
R – Group determines solubility.
Glucose is a polar molecule. It dissolves and is carried in the blood plasma.

14. Oxygen gas is non-polar. It is small so has some solubility in water.
Most is carried by the erythrocyte (red blood cells).
Each hemoglobin has 4 bonding sites for oxygen.
NaCl is an ionic compound
Dissolves in water
Carried in the plasma

15. Cholesterol has a small hydrophilic portion.
Not enough to be water soluble
Carried by a lipoprotein complex in the plasma.
Fats are large and non polar
Not water soluble
Carried by lipoprotein complex in the plasma.
Lipoprotein complex:
has phospholipids on surface that anneal to water
Hydrophobic fats on inside; cholesterol is positioned so that hydrophilic portion faces outward.
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