1. Lecture #3 Properties of H20
Unit – Biochemistry

2. http://video. nationalgeographic

3. Water is one of the few compounds found in a liquid state over most of Earth’s surface.
Water is essential for life for the following three reasons

4. 3 Important Properties of Water
Water has a high Heat Capacity
 Because of the multiple hydrogen bonds between water molecules, it takes a large amount of heat energy to cause those molecules to move faster and raise the temperature of the water.

5. Water’s heat capacity is relatively high Heat Capacity - the amount of heat energy required to increase its temperature Why is this important for living things?

6. Reason #1: Large bodies of water, such as oceans and lakes, can absorb large amounts of heat with only small changes in temperature. This protects organisms living within from drastic changes in temperature.
Reason #2: (Homeostasis) At the cellular level, water absorbs the heat produced by cell processes, regulating the temperature of the cell.

7. Take two minutes to summarize what you have learned about this property of water.

8. 2. Water easily dissolves polar & ionic compounds
Solution - a mixture in which one or
more substances are evenly distributed
in another substance.
Water forms solutions easily.
This is important because it is how many important because substances such as salts, sugars, minerals, & gases in the body can move within and between cells!
Water is forms solutions easily because it is a
POLAR MOLECULE .

9. Add these to your notesheet!!
A solution is made of two things:
Solvent- the dissolving substance in a solution.
2. Solute- substance that is dissolved in a solution.

10. Water (the universal solvent) forms solutions easily because it is a POLAR molecule
What does it mean to
be polar?
Answer
Polar molecules have a partial positive charge on one side and a partial negative charge on the other side.
This uneven distribution of charge is due to oxygen’s strong attraction for electrons (due to 8 protons in the nucleus) when compared to the attraction for electrons that hydrogen has (1 proton in the nucleus)

11. Example of how water’s polarity helps to form solutions – Salt Crystal Dissolving
H20 surrounds the ionic substance. (NaCl)
Ions are attracted to the ends of the H20 molecule with the opposite charge.
The ions get pulled apart and the resulting solution is a mixture of H20 molecules and ions.
Polar molecules are dissolved by a similar attraction.
Ionic and Polar compounds are considered hydrophilic, or ‘water loving’.

12. Non-polar compounds do NOT dissolve well in water.
Why does this happen?
The H20 molecules (polar) are more attracted to each other than to the nonpolar molecules.
Nonpolar molecules such as lipids have no negative or positive poles & are hydrophobic or ‘water fearing’)

13. The interaction between H20 & nonpolar molecules is important to living organisms.
Ex: The shape & function of cell membranes depends on the interaction of polar H20 with nonpolar membrane molecules (phospholipids).

14. Take two minutes to summarize what you have learned about this property of water.

15. 3. Water binds itself to other substances
Cohesion - attraction
between molecules of
the same substance
The hydrogen bonds between water molecules causes cohesion of liquid water.
This is what causes water and other liquids to form drops.

16. Surface Tension is the result of cohesion
This attraction between water molecules produces a force sometimes known as SURFACE TENSION; which can support very lightweight objects. Surface tension prevents the surface of water from stretching or breaking easily.

17. Adhesion – force of attraction between different kinds of molecules Example #1 -a ‘sweating’ cup Example #2 -morning dew

18. Capillary Action- The tendency of water to rise in a thin tube

19. Capillary Action in Plants
In a plant, H20 molecules move upward
through the roots & stem of a plant to its
leaves due to a combination of
capillary action, cohesion and other
factors
The attraction of water to the walls of the stem (adhesion) sucks the water up more than gravity pulls it down.
Water ‘pulls’ water (cohesion)up the stem

20. Example of Capillary Action

21. Take two minutes to summarize what you have learned about this property of water.

22. How important is water to life?
Water surrounds all cells, is found inside of all cells, and influences the shape of the cell membrane. Most of the reactions that take place in a cell can only occur in the presence of water!