1. Molecular Movement Across Membranes

2. What you need to know! How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution How electrochemical gradients are formed.

3. Diffusion The movement of molecules from an area of high concentration to an area of low concentration Resulting in even distribution when equilibrium is reached Reason: random movement of all molecules driven by kinetic energy (temperature/pressure) Cells do not invest energy (no ATP)

4. Diffusion in and out of cells Plasma membrane is selectively permeable (semi-permeable) Permeable for very small, uncharged, hydrophobic molecules and gases Impermeable for ions and large molecules Use of transport proteins/pores embedded in the membrane No energy needed due to concentration gradient

5. Examples of Diffusion O2/CO2 exchange between blood and cells Sugar molecules/pores Small waste molecules-urea Amino acids/pores Lipids

6. Osmosis Definition: diffusion of water molecules across a semi-permeable membrane All water movements in cells or organisms through osmosis Water molecules use aquaporin proteins Water will always go in the direction of lower water concentration (high solute concentration) or lower water potential

7. Osmosis in Cells 2 parameters: 1.Solute concentration (salt, sugar, other substances…) 2.Water concentration: –High solute (salt, sugar, etc.) concentration usually means low water concentration –Low solute (salt, sugar, etc.) concentration usually means higher water concentration –Distilled water is solute free (100% water)

8. How to answer Osmosis Questions Compare the inside water concentration with the outside water concentration: Isotonic: inside and outside same concentration of solute (and water) Hypertonic: solution with higher solute concentration (lower water) Hypotonic: solution with lower solute concentration (higher water)

9. Living Cells in solutions a)Low salt water (same salt concentration inside and outside the cell = isotonic) no change in shape b)Strong salt water (more salt outside the cell = hypertonic; inside = hypotonic) cell shrivles c)Distilled water (no salt outside = hypotonic; inside = hypertonic) cell explodes