Diffusion & Osmosis

1. Diffusion & Osmosis

2. Diffusion • The random movement of molecules from a area of higher concentration to an area of lower concentration (the net movement of molecules down a concentration gradient)

3. Concentration • Refers to how crowded particles are. • Generally, particles spread out (move away) to be less concentrated. Solution=2 substance Solute-concentrate Solvent-Water

4. Notes • Take out paper • Follow along

5. OSMOSIS • The diffusion of water across a selectively permeable membrane is called osmosis. • Regulating the water flow through the plasma • membrane is an important factor in maintaining • homeostasis within a cell.

6. Section 8.1 Summary – pages 195 - 200 What controls osmosis? • Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis. Before Osmosis After Osmosis Selectively permeable membrane Water molecule Sugar molecule

7. Section 8.1 Summary – pages 195 - 200 Cells in an isotonic solution • Most cells whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions. H2O H2O Water Molecule Dissolved Molecule

8. Section 8.1 Summary – pages 195 - 200 Cells in an isotonic solution • In an isotonic solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell. • In an isotonic solution, water molecules move into and out of the cell at the same rate, and cells retain their normal shape. H2O H2O Water Molecule Dissolved Molecule

9. Section 8.1 Summary – pages 195 - 200 Cells in an isotonic solution • A plant cell has its normal shape and pressure in an isotonic solution.

10. Section 8.1 Summary – pages 195 - 200 Cells in a hypotonic solution • In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell. H2O H2O Water Molecule Dissolved Molecule

11. Section 8.1 Summary – pages 195 - 200 Cells in a hypotonic solution • Plant cells swell beyond their normal size as pressure increases.

12. Section 8.1 Summary – pages 195 - 200 Cells in a hypertonic solution • In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink. H2O H2O Water Molecule Dissolved Molecule

13. Section 8.1 Summary – pages 195 - 200 Cells in a hypertonic solution • Plant cells lose pressure as the plasma membrane shrinks away from the cell wall.

14. Section 8.1 Sumary – pages 195 - 200 Passive Transport • When a cell uses no energy to move particles across a membrane passive transport occurs. Concentration gradient Plasma membrane

15. Exploration • HOW CELLS DEAL WITH OSMOSIS • 1. Cells that are expose to an Isotonic External environment Usually have no difficulty keeping the movement of water across the cell membrane in balance. • 2. This is the case with the cells of vertebrate animals on land and most other organisms living in the sea. • 3. Plant cells can live in Hypotonic environment. The Cells that make up the roots may be surrounded by water. • 4. Water moves by Osmosis into Plant Cells, which Swell as they fill with water. The Swelling stops when the Cell Membrane is pressed against the Cell Wall.

16. 5. The Cell Wall is strong enough to resist the pressure, the pressure that water molecules exert against the Cell Wall is called TURGOR PRESSURE. • 6. In a Hypertonic environment, Water Leaves the Cells through Osmosis. The Cells Shrink away from the Cell Wall, and Turgor Pressure is lost. This condition is called PLASMOLYSIS, and is the reason Plants Wilt. • 7. Animal Cells placed in a Hypertonic environment will have Water leave the cells, making them shrink and shrivel. • 8. Place in a Hypotonic environment, Water Diffuses into the cells, causing them to Swell and eventually Burst - CYTOLYSIS.

17. Closure/Recap • Diffusion- movement of molecules from an area of higher concentration to an area of lower concentration • Osmosis- the diffusion of water across a semipermeable membrane. • Isotonic, Hypotonic, Hypertonic • Passive Transport