1. Why is water so important to living systems???
Water & Diffusion
Why is water so important to living systems???

2. The Importance of Water
Most life processes occur only when molecules are dissolved in water.
Serves as a means of material transport
Makes up 70 to 95% of most organisms

3. Water is polar
Means that the atoms making up water share electrons in a covalent bond but share them unequally
Each molecule has a positive end and a negative end
Water molecules attract each other as well as ions and other polar molecules
Water dissolves many ionic compounds
It is an excellent solvent

4. Hydrogen Bonds
It is a weak bond
Helps hold large molecules together

5. Results of polarity
Capillary action and Surface tension of water help it get from soil to the tops of tall trees

6. Resists Temperature Change
Acts as an insulator, helping maintain a steady environment
Since cells exist in a mostly water environment this helps cellular homeostasis

7. Expands when it freezes
Ice is less dense than water
Causes rocks to form cracks over time by freezing and thawing

8. Diffusion Kinetic energy- energy of motion
Brownian Motion- random motion of molecules
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9. Process
Diffusion is the movement of particles from areas of greater concentration to areas of lower concentration
Caused by the random movement of molecules
The more concentrated the substance, the more rapid is the rate of diffusion
Increasing the temperature also increase the rate

10. Results of Diffusion
Diffusion occurs until dynamic equilibrium is reached
There is continuous movement of molecules but no overall concentration change

11. Living Systems Molecules in cells are in a water solution
Difference in concentration of substances across a space is a concentration gradient
Diffusion moves substances from high to low concentrations
Diffusion moves with the gradient and continues until dynamic equilibrium is reached
OSMOSIS IS THE DIFFUSION OF WATER ACROSS A SELECTIVELY PERMEABLE MEMBRANE!