Diffusion and Osmosis

1. Diffusion and Osmosis 3.4

2. KEY CONCEPT • Materials move across membranes because of concentration differences.

3. Diffusion and Osmosis • Molecules can move across the cell membrane through passive transport. • Passive transport does not require energyinput from a cell • There are two types of passive transport • Diffusion • Osmosis

4. Diffusion • Diffusion is the movement of molecules in a fluid or gas from high concentration to low concentration • Molecules diffuse down a concentration gradient. • “Move downhill” or from • high to low

5. Diffusion • Diffusion stops when dynamic equilibrium (spread evenly, but molecules still moving) is reached

6. Diffusion • Concentration • Number of molecules in a substance in a given volume • Concentration gradient • Difference in concentration from one area to another

7. Diffusion • Diffusion plays a key role in cells ability to move substances into and out of the cell • Small lipids and nonpolar molecules like O2 and CO2 diffuse easily • Cells continually consume O2 • Therefore the concentration of O2 is almost always higher outside the cell • Result O2 diffuses into cell without the need of energy

8. Osmosis • Osmosis is the diffusion of water molecules across a semipermeable membrane from high water molecule concentration to low H20 concentration. • Continues until dynamic equilibrium is reached

9. Osmosis • Homeostasis • Biological Balance • Key concept of selectively permeable membrane and osmosis is to maintain homeostasis!

10. Osmosis • Tonicity • A measure of water pressure against a semipermeable membrane • Three types of Tonicity 1. Isotonic • Concentration of solute is equal inside and outside of cell

11. Cell in Isotonic Solution 10% NaCl90% H2O ENVIRONMENT CELL NO NET MOVEMENT 10% NaCl 90% H2O What is the direction of water movement? The cell is at _______________. equilibrium

12. Osmosis • 2. Hypertonic • The concentration of solute is greater outside the cell • Plasmolysis – The process by which the cell shrinks from losing water

13. Cell in Hypertonic Solution 15% NaCl85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O What is the direction of water movement?

14. Osmosis • 3. Hypotonic • The concentration of solute is greater inside the cell • Cytolysis – The process by which a cell bursts from water entering • Turgor pressure – Pressure exerted on the cell wall of plants due to water pushing out

15. Cell in Hypotonic Solution 10% NaCl90% H2O CELL 20% NaCl 80% H2O What is the direction of water movement?

16. Osmosis • Some single celled organisms and animals are adapted to survive hypotonic solutions • They have structures (cell wall and vacuole) to store or remove (contractile vacuole) excess water

17. Practice • Draw arrows to indicate the direction of water movement into cell, out of cell, or both! • The 10% solution represents a cell

18. Video • Tonicity and osmosis

19. Some Molecules diffuse through transport proteins • Facilitated Diffusion • Some molecules cannot easily diffuse across the cell membrane. • A transport or carrier protein provides a door for a substance to enter the cell. Square peg in a round hole idea! • Still No energy is used