2. Plasma Membrane Function Maintains balance by controlling what enters and exits the cell What characteristic of life is this? HOMEOSTASIS Membrane is selectively permeable  only allows certain molecules through

3. Plasma Membrane Structure Phospholipid Bilayer (2 layers of lipids) Polar heads face out because they are hydrophilic Nonpolar tails face in because they are hydrophobic “water loving”

4. Fluid Mosaic Model

5. Plasma Membrane Structure Fluid Properties: Unsaturated fatty acid tails Cholesterol in animal membranes

6. Plasma Membrane Structure Mosaic Properties Proteins in the lipid bilayer Integral proteins are inside the membrane Peripheral proteins are only found on one side of the membrane

7. Integral Protein Examples Channel – allow materials to pass through (tunnel) Carrier – transport materials across Receptor – transmit information Marker – identify the cell to other cells

9. 9 Diffusion of Liquids

10. Diffusion Solute particles move from HIGH concentration to LOW concentration This always occurs when there is a concentration gradient It will continue until dynamic equilibrium is reached

11. Diffusion Demonstration 1. What solution is being put into the bag? What color is it? starch & water; cloudy white 2. What solution is in the beaker? What color is it? iodine & water; amber 3. Predict what will happen to the bag and/or beaker color(s).

12. Diffusion Demonstration Results 1. What color is the bag? 2. What color is the beaker? 3. Explain what happened. Iodine molecules were small enough to fit across the membrane. Starch molecules were too large. The solution turned blue when starch & iodine mixed.

14. Diffusion review Movement of particles from HIGH concentration to LOW concentration This is caused by a concentration gradient It will stop when dynamic equilibrium is reached

15. Osmosis Diffusion of water molecules across a selectively permeable membrane Occurs when the solute particles (dots) cannot pass through the membrane

16. Osmotic Solutions Hypotonic = lower concentration (less dots) Hypertonic = higher concentration (more dots)

17. 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

18. Cells in an isotonic solution water molecules move into and out of the cell at the same rate, and cells retain their normal shape. H2OH2O H2OH2O Water Molecule Dissolved Molecule

19. Cells in an isotonic solution water molecules move into and out of the cell at the same rate, and cells retain their normal shape. H2OH2O H2OH2O Water Molecule Dissolved Molecule

20. Cells in an isotonic solution A plant cell has its normal shape and pressure in an isotonic solution.

21. Cells in a hypotonic solution hypotonic solution: dilute solution thus low solute concentration In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell. H2OH2O H2OH2O Water Molecule Dissolved Molecule

22. Cells in a hypotonic solution Plant cells swell beyond their normal size as pressure increases. (plants prefer this – it makes the leaves firm) Turgor Pressure – water pushing the plasma membrane against plant cell wall

23. Cells in a hypertonic solution hypertonic solution: concentrated solution, thus a high solute concentration In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink H2OH2O H2OH2O Water Molecule Dissolved Molecule

24. Cells in a hypertonic solution Plant cells lose pressure as the plasma membrane shrinks away from the cell wall. PLASMOLYSIS – shrinking of cytoplasm away from cell wall due to outward water flow

25. Isotonic = equal concentration Osmotic Solutions

26. Direction of Water Hypotonic solutions = water moves INTO the cell Hypertonic solutions = water moves OUT of the cell Isotonic solutions = NO net movement of water

27. Effects on different cells Animal Cell Plant Cell Solution Hypotonic Hypertonic Isotonic burst shrivel normal Turgor pressure plasmolysis limp

29. Passive Transport Movement of particles from HIGH concentration to LOW concentration Requires NO energy 3 types: 1. Diffusion 2. Osmosis 3. Facilitated diffusion

30. Facilitated Diffusion Diffusion of particles across a membrane using transport proteins Uses both channel and carrier proteins

32. Active Transport Movement of particles from LOW concentration to HIGH concentration Requires cell energy 3 types: 1. Pumps 2. Endocytosis 3. Exocytosis

33. Active Transport Pumps -use carrier proteins to push/pull molecules across the membrane

34. Active Transport Endocytosis - Transport of very large molecules INTO the cell - Forms a vacuole Exocytosis - Release of very large molecules (from a vacuole or vesicle) OUT of the cell