1. The Organization of Life November 3, 2009

2. Section 2 Objectives – page 152 Section Objectives Identify how the process of diffusion occurs and why it is important to cells. Relate water’s unique features to polarity.

3. Summary Section 2 – pages 152-156 Water is perhaps the most important compound in living organisms. Water and Its Importance Water makes up 70 to 95 percent of most organisms.

4. Summary Section 2 – pages 152-156 Water is Polar A polar molecule is a molecule with an unequal distribution of charge; that is, each molecule has a positive end and a negative end. Water is an example of a polar molecule. Water can dissolve many compounds, such as salt, and many other polar molecules, such as sugar.

5. Summary Section 2 – pages 152-156 Water is Polar Water molecules also attract other water molecules this makes water cohesive.

6. Summary Section 2 – pages 152-156 Water resists changes in temperature. Therefore, water requires more heat to increase its temperature than do most other common liquids. Water resists temperature changes

7. Summary Section 2 – pages 152-156 The process of diffusion Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. Three key factors—concentration, temperature, and pressure—affect the rate of diffusion.

8. Summary Section 2 – pages 152-156 The results of diffusion When a cell is in dynamic equilibrium with its environment, materials move into and out of the cell at equal rates. As a result, there is no net change in concentration inside or outside the cell. Material moving out of cell equals material moving into cell

9. Summary Section 2 – pages 152-156 Diffusion in living systems The difference in concentration of a substance across space is called a concentration gradient. Ions and molecules diffuse from an area of higher concentration to an area of lower concentration, moving with the gradient. Dynamic equilibrium occurs when there is no longer a concentration gradient.