Membrane Structure and Water

1. Membrane Structure and Water Objective 2.03 How cells maintain homeostatsis Movement of materials into and out of cells

2. Homeostasis…. remember that?!?! • Maintaining a stable internal environment that is balanced!

3. Homestasis Example

4. A little FYI about water • The universal solvent – a lot of things can dissolve in it. • Makes up 70 – 95% of most organisms

5. More about water • Water is a polar molecule. • This means it has a positive end and a negative end. • This makes it able to dissolve MANY substances.

6. Plasma Membrane: Structure and Function

7. Plasma/Cell Membrane • In an animal cell, it is the boundary between the cell and its environment. • In a plant cell, it is between the cell wall and the cytoplasm of the cell.

8. The Role of the Plasma Membrane • To maintain HOMEOSTASIS!!!!

9. The Plasma Membrane… • It is selectively permeable. • It is choosy about what enters and leaves the cell. • It keeps the good stuff (nutrients) in and the bad/harmful substances out.

10. The Model of the Plasma Membrane • Referred to as the Fluid Mosaic Model. • Fluid – the parts that make up the membrane are always moving • Mosaic – the membrane is made up of many different substances that make a pattern.

11. Membrane Structure • The plasma membrane is a PhospholipidBilayer Phosphate + Lipid Two layers Other parts: Proteins, cholesterol and carbohydrates

12. Phospholipids • The “heads” • Hydrophilic – water loving • Polar • Attracted to water • The “tails” • Hydrophobic – water fearing • Non-polar • Oriented to the middle of the plasma membrane

14. Can things move through the cell membrane? • You BET!!!! • If they are small, they can go through without the cell using any energy. • Water and oxygen • If they are large, they have to use a special type of protein that uses energy. • Sugar

15. Membrane Transport

16. Two Types of Cell Transport Passive Transport Active Transport Energy required Movement of materials is from low to high concentration. Materials move UP a concentration gradient. Requires the use of proteins. • No energy required. • Movement of materials from high to low concentration. • Materials move DOWN a concentration gradient. • Examples are diffusion, osmosis and facilitated diffusion

17. What is Concentraiton Gradient? • When the concentrations of two solutions is different.

18. Passive Transport • Movement of particles from a area of high concentration to an area of low concentration. • Does not require energy to be used.HIGH concentration of solute (ex. Salt) Inside a cell LOW Concentration of solute (ex. Salt)

19. Diffusion • Movement of particles from an area of high concentration to an area of low concentration. • Goal = reach dynamic equilibrium = inside and outside the cell are at equal concentrations.

21. Facilitated Diffusion • Same as diffusion but uses a protein in cell membrane • Used for particles that are too big to squeeze through the cell membrane.

22. Transport Proteins for Facilitated Diffusion • Channel Protein – does not change shape • Carrier Protein – can change shape

23. Osmosis • The diffusion of water across a selectively permeable membrane. • Water is moving from high to low.

24. What happens to cells when placed in…. • A hypertonic solution (like syrup) Water moves out. The cell shrinks.

25. What will happen when a cell is placed in a …. • Hypotonic solution (like pure water) Water will move into the cells causing it to get larger.

26. What will happen when a cell is placed in…. • An Isotonic solution…. Water will move into and out of the cell at equal rates. This cell has reached dynamic equilibrium.

27. A Summary of Osmotic Situations

28. Yet another way to look at it…

29. An Animation • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

30. Active Transport • Requires ENERGY!!! • Movement is from LOW to HIGH • Uses transport proteins (carrier or channel)

31. Something to think about….