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The Organization of Life. November 3, 2009. Section 2 Objectives – page 152. Section Objectives. Relate water’s unique features to polarity. Identify how the process of diffusion occurs and why it is important to cells. Summary Section 2 – pages 152-156. Water and Its Importance.
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The Organization of Life November 3, 2009
Section 2 Objectives – page 152 Section Objectives • Relate water’s unique features to polarity. • Identify how the process of diffusion occurs and why it is important to cells.
Summary Section 2 – pages 152-156 Water and Its Importance • Water is perhaps the most important compound in living organisms. • Water makes up 70 to 95 percent of most organisms.
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.
Summary Section 2 – pages 152-156 Water is Polar • Water molecules also attract other water molecules this makes water cohesive.
Summary Section 2 – pages 152-156 Water resists temperature changes • Water resists changes in temperature. Therefore, water requires more heat to increase its temperature than do most other common liquids.
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.
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
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.
