1. العلم شجرة والعمل ثمرتها
العلم شجرة والعمل ثمرتها

2. Chapter 2 Basic Chemistry pages 26-34 2
Chapter 2 Basic Chemistry pages Chemistry of Water (page 26) 2.4 Acids and Bases (page 32-33)

3. Chemistry of water In biology, the structure relates to function.
This is true at a variety of organizational levels, including molecules such as water.
The shape of water ( H2O ) molecule and its polarity result in the formation of hydrogen bonds.
A hydrogen bond is caused by the attraction of slightly positive hydrogen to a slightly negative atom in the vicinity.

5. H-bonds are not unique to water.
Other biological molecules, such as DNA, have polar covalent bonds involving an electropositive hydrogen and usually an electronegative oxygen or nitrogen. In these instances, a hydrogen bond can occur within the same molecule or between nearby molecules.
Although a single hydrogen is more easily broken than a single covalent bond, multiple hydrogen bonds are collectively quite strong.
Protein
DNA

6. Properties of water The 1st cell (s) evolved in water.
All living things are 70-90% water.
Due to hydrogen bonding water molecules cling together
Because of hydrogen bonding:-
- water is a liquid at temperatures typically
found on the Earth's surface.
- It freezes at 0°C and boils at 100°C.

7. Water:
1. Has a high heat capacity
2. Has a High Heat of Evaporation
3. Is a solvent
4. Molecules are cohesive and adhesive
5. Frozen water (ice) is less dense than liquid water

8. Figure 2. 10 Temperature and water
Figure 2.10 Temperature and water. Water can be solid, a liquid, or a gas at naturally occurring environmental temperatures. At R.T. and pressure, water is a liquid, when water freezes and becomes a solid (ice), it gives off heat, and this heat can help keep the environmental temperature higher than expected. On the other hand, when water evaporates, it takes up a large amount of heat as it changes from a liquid to a gas. Heat Content of Water at Various Temperatures

11. Fig. 2.11 Water molecules are cohesive and
adhesive.

12. The high surface tension allows the water strider to walk on a pond without breaking the surface.

13. Fig. 2.12 Ice is less dense than liquid water

14. A Pond in Winter

15. Acids and Bases
Acids are substances that dissociate in water, releasing H+
Bases are substances that either take up H+ or release OH-
pH Scale used to indicate the acidity or basicity (alkalinity) of a solution
The pH scale ranges from 0 to 14
pH scale is the negative log of the [H+]
Examples: pH of blood is about 7.4,
pH of stomach is about 2

16. The pH scale

17. Buffers and pH
Buffer is a chemical or combination of chemicals that keeps the pH within normal limits.
In living things, the pH of body fluids is maintained within a narrow range, or else molecules don’t function correctly and our health suffers.
pH of blood in healthy person is about 7.4 (just slightly basic (alkalline)
- If the blood pH drops to about 7, acidosis results.
- If the blood pH rises to about 7.8, alkalosis results.
- Both conditions can be life threatening, the blood pH must
be kept around 7.4.
Normally, pH stability is possible because the body has built-in mechanisms to prevent pH changes.
Buffers are one of these important mechanisms

18. Blood always contains a combination of some carbonic acid and bicarbonate ions that act as a buffering system in the blood.
When H+ are added to blood, the following reaction reduces acidity:
H+ + HCO ► H2CO3
When OH- are added to blood, this reaction reduces basicity:
OH H2CO ► HCO H2O
These reactions prevent any significant change in blood pH.

19. It is the weak who are cruel. can only be expected from the strong
Gentleness
can only be expected from the strong

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