2. Role of Cell Membrane It serves as an outer boundary of cells. The cell membrane is selectively permeable. It controls what enters and leaves the cell. It lets some things enter and leave and not others

3. Phospolipid bilayer Phospolipid – a lipid and two fatty acids The head is polar and the tails are non-polar Polar – attracted to water Nonpolar – repels water Arranged in two layers

4. Transport through cell membranes For the cell to survive some materials need to be able to enter and leave the cell. There are 4 basic mechanisms: 1. DIFFUSION and FACILITATED DIFFUSION 2. OSMOSIS 3. ACTIVE TRANSPORT 4. BULK TRANSPORT

5. Passive Transport Movement of molecules from an area of high concentration to an area of low concentration. Examples Diffusion Osmosis Facilitated diffusion

6. Diffusion Diffusion is the net movement of molecules (or ions) from a region of their high concentration to a region of their lower concentration. The molecules move down a concentration gradient. As a result of diffusion molecules reach an equilibrium where they are evenly spread out, and there is no net movement of molecules from either side. Examples – Oxygen, Carbon Dioxide, and Water

7. Diffusion of Liquids

8. DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make the molecules move.

9. Diffusion through a membrane Cell membrane Inside cell Outside cell

10. Diffusion through a membrane Cell membrane Inside cell Outside cell diffusion

11. Diffusion through a membrane Cell membrane Inside cell Outside cell EQUILIBRIUM

14. What determines the rate of diffusion? There 4 factors: 1. The steepness of the concentration gradient. 2. Temperature. 3. The surface area. 4. The type of molecule or ion diffusing.

15. Osmosis: ‘The diffusion of water from an area of high concentration of water molecules to an area of low concentration of water across a semi-permeable membrane.’

16. Osmosis Cell membrane partially permeable. Inside cell Outside cell VERY High conc. of water molecules. VERY Low conc. of water molecules. High water potential. Sugar molecule DILUTE SOLUTION CONCENTRATED SOLUTION

17. Osmosis Cell membrane partially permeable. Inside cell Outside cell High conc. of water molecules. Low conc. of water molecules. High water potential. OSMOSIS

18. Osmosis Cell membrane partially permeable. Inside cell Outside cell OSMOSIS EQUILIBRIUM. Equal water concentration on each side. Equal water potential has been reached. There is no net movement of water

21. Direction of Osmosis HypotonicHypertonicIsotonic Solute higher inside cell than outside Solute molecules higher outside cell than inside Solute is equal inside and outside of the cell Water tends to flow from hypotonic to hypertonic solutions

23. Hypotonic, Hypertonic, & Isotonic Solutions If the fluid outside the cell has… Then outside fluid is … Water diffuses...Effect on cell …lower water concentration than cytosol hypertonicOut of cellCell shrinks …higher water concentration than cytosol hypotonicInto cellCell swells …same water concentration as cytosol IsotonicInto and out of cell at equal rates Cell stays same size

24. Passive Transport Video Clip

25. Facilitated Diffusion Large polar molecules such as glucose and amino acids, cannot diffuse across the phospholipid bilayer. Also ions such as Na + or Cl - cannot pass. These molecules pass through Carrier Proteins instead. Diffusion through these channels is called FACILITATED DIFFUSION. Movement of molecules is still PASSIVE just like ordinary diffusion, the only difference is, the molecules go through a protein channel instead of passing between the phospholipids.

26. Facilitated diffusion

28. Facilitated Diffusion through a membrane Cell membrane Inside cell Outside cell Protein channel

29. Facilitated Diffusion through a membrane Cell membrane Inside cell Outside cell Protein channel diffusion

30. Facilitated Diffusion through a membrane Cell membrane Inside cell Outside cell Protein channel diffusion EQUILIBRIUM

31. Facilitated Diffusion: Molecules will randomly move through the opening like pore, by diffusion. This requires no energy, it is a PASSIVE process. Molecules move from an area of high concentration to an area of low conc.

32. These are carrier proteins. They do not extend through the membrane. They bond and drag molecules through the bilipid layer and release them on the opposite side.

33. ACTIVE TRANSPORT Requires input of energy Molecules moves against the concentration gradient Sodium Potassium Pump

34. Active Transport:

37. Passive transport video clip

38. Bulk Transport:

39. EXOCYTOSIS (Movement out of cell) Large molecules that are manufactured in the cell are released through the cell membrane.

40. Vesicle-Mediated Transport Vesicles and vacuoles that fuse with the cell membrane may be utilized to release or transport chemicals out of the cell or to allow them to enter a cell. Exocytosis is the term applied when transport is out of the cell. VesiclesvacuolesExocytosis

41. ENDOCYTOSIS is the case when a molecule causes the cell membrane to bulge inward, forming a vesicle. PHAGOCYTOSIS is the type of endocytosis where an entire cell is engulfed. “cell eating” PINOCYTOSIS is when the external fluid is engulfed. “cell drinking” Examples include the transport of insulin and cholesterol into animal cells.