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Explore the significance of water in living organisms, its unique properties, and the process of diffusion within cells. Learn about water's polarity, cohesive nature, and ability to resist temperature changes. Understand diffusion and dynamic equilibrium in maintaining cell balance.
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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.