Chapter 5 Diffusion and Osmosis

Diffusion – What is it? – Why does it occur? – What is misleading about the way the molecules are drawn in the equilibrium diagram?

Net diffusion Diffusion of two solutes Equilibrium © 2014 Pearson Education, Inc. Note that each substance diffuse down its own concentration gradient, unaffected by the concentration gradients of other substances.

H2OH2O Sugar molecule Lower concentration of solute (sugar) Higher concentration of solute © 2014 Pearson Education, Inc. Osmosis What is it? More similar concen- trations of solute Lost mass Gained mass

Figure 5.10b Selectively permeable membrane Osmosis Water molecules can pass through pores, but sugar molecules cannot. Water molecules cluster around sugar molecules. This side has fewer solute mol- ecules, more free water molecules. This side has more solute mol- ecules, fewer free water molecules. © 2014 Pearson Education, Inc.

Water Balance of Cells Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water. © 2014 Pearson Education, Inc.

Water Balance of Cells net Isotonic solution: Solute concentration outside of the cell is the same as inside the cell; no net water movement across the plasma membrane. © 2014 Pearson Education, Inc. Flaccid H2OH2O H2OH2O

Water Balance of Cells Hypertonic solution: Solute concentration outside of the cell is greater than that inside the cell; cell loses water. © 2014 Pearson Education, Inc. Plasmolyzed H2OH2O

Water Balance of Cells Hypotonic solution: Solute concentration outside of the cell is less than that inside the cell; cell gains water. © 2014 Pearson Education, Inc. Lysed H2OH2O Hypotonic Animal cell Turgid (normal) Cell wall H2OH2O Plant cell