DIFFUSION, OSMOSIS AND THE CELL MEMBRANE

1. DIFFUSION, OSMOSIS AND THE CELL MEMBRANE

2. DIFFUSION • Diffusion is the movement of molecules from high to low concentration. • Give some everyday examples of diffusion. • Diffusion continues until there is an equal number moving in both directions. This is called equilibrium.

3. Movement of Materials • Diffusion – molecules of a substance move from higher concentrated areas to lower concentrated areas (no control – uses no energy – passive).

4. Osmosis • A special kind of diffusion is osmosis which is diffusion of water across a membrane. It still moves from high to low concentration. • Hypertonic is when there is more water INSIDE the cell than outside. So, water moves out. What happens to the cell? The cell shrivels up and it is called plasmolysis. • What happens if you put salt on a slug? • What happens if you get salt on a plant?

5. PLASMOLYSIS

6. HYPOTONIC • Hypotonic is when there is LESS water inside a cell than outside. What happens? • Water moves into the cell. An animal cell may swell and break open. This is called cytolysis. • This doesn’t happen with a plant cell. Why? Water pressure in a plant cell is called turgor pressure.

7. HYPOTONIC

8. ISOTONIC • Equal amounts on both sides of membrane. Homeostasis.

10. CELL MEMBRANE • The cell or plasma membrane is the most important structure to help the cell maintain balance or homeostasis. The membrane regulates what goes in an out of the cell.

11. Structure of cell membrane The cell membrane is a bilayer made of phospholipids. How many layers are there? What is a phospholipid? A phospholipid is made up of one phosphate and two fatty acids. The phosphate is the head. The fatty acids are tails.

12. Phospholipid – has both polar and non polar regions. • Head made of phosphorus and nitrogen; polar; loves water • Tail made of fatty acid; non polar; hates water

13. The head is hydrophilic. What does that mean? • The tail is hydrophobic. What does that mean? (Remember that the tail is the fat.)

15. How does it work? • Some things such as oxygen and carbon dioxide can pass through easily. • Other things such as sugar, do not pass through as easily. • The membrane is selective as to what can go through. Therefore, it is selectively permeable or semi-permeable.

16. Proteins • Embedded in the phospholipidbilayer are proteins. They float about and help things move through. The membrane is called a fluid mosaic membrane because the proteins can move around.

17. Channel proteins make pathways for water to pass through. • Carrier proteins help digested food to pass through.

18. PASSIVE TRANSPORT • Both diffusion and osmosis are forms of passive transport because they do not require energy on the part of the cell.

19. ACTIVE TRANSPORT • Active transport requires the cell to use energy. • Endocytosis means to bring a substance into a cell. • Exocytosis means to move a substance out of a cell. • The cell makes a small pouch out of the membrane. This is called a vesicle. • Examples:

23. Cell membrane proteins functions • 1.Important chemical reactions. • 2.Help cells communicate and recognize each other. • 3.Move substances across membrane. • Animation: How Diffusion Works