The plasma membrane functions as a selective barrier controlling what passes in and out of cells. It is composed of lipids and proteins arranged in the fluid mosaic model, where lipids form a fluid bilayer and proteins float freely within it. Materials cross the membrane through passive transport mechanisms like diffusion, osmosis, and facilitated diffusion which do not require energy, or active transport processes like carrier-mediated transport, endocytosis, and exocytosis which use cellular energy.

1. Membrane Structure and Function

2. Plasma Membrane The membrane at the boundary of every cell. Functions as a selective barrier for the passage of materials in and out of cells.

3. Membrane Composition Lipids Proteins

4. Fluid Mosaic Model Refers to the way the lipids and proteins behave in a membrane.

5. “Fluid” Refers to the lipid bilayer. Molecules are not bonded together, so are free to shift. Must remain "fluid" for membranes to function.

6. “Mosaic” Proteins: float in a sea of lipids. Proteins form a collage or mosaic pattern that shifts over time.

8. Protein Function in Membranes Transport. Enzymatic activity. Receptor sites for signals. Cell adhesion. Cell-cell recognition. Attachment to the cytoskeleton.

10. Types of Membrane Proteins Integral - inserted into the lipid bilayer. Peripheral - not embedded in the lipid bilayer, but are attached to the membrane surface.

12. Membranes are Bifacial The lipid composition of the two layers is different. The proteins have specific orientations. Carbohydrates are found only on the outer surface.

13. Question How do materials get across a cell's membrane?

14. Problems Lipid bilayer is hydrophobic. Hydrophilic materials don't cross easily. Large molecules don't cross easily. Too big to get through the membrane.

15. Mechanisms 1. Passive Transport 2. Active Transport

16. Passive Transport Movement across membranes that does NOT require cellular energy.

17. Types of Passive Transport 1. Diffusion 2. Osmosis 3. Facilitated Diffusion

18. Diffusion The net movement of atoms, ions or molecules down a concentration gradient. Movement is from: High Low

20. Equilibrium When the concentration is equal on both sides. There is no net movement of materials.

21. Factors that Effect Diffusion 1. Concentration 2. Temperature 3. Pressure 4. Particle size 5. Mixing

22. Osmosis Diffusion of water. Water moving from an area if its high concentration to an area of its low concentration. No cell energy is used.

23. Tonicity The concentration of water relative to a cell. 1. Isotonic (same) 2. Hypotonic (below) 3. Hypertonic (above)

25. Isotonic Isosmotic solution. Cell and water are equal in solute concentration. No net movement of water in or out of the cell. No change in cell size.

26. Hypotonic Hypoosmotic solution Cell's water is lower than the outside water (more solutes). Water moves into the cell. Cell swells, may burst or the cell is turgid.

27. Hypertonic Hyperosmotic solution Cell's water is higher than the outside water (less solutes) Water moves out of the cell. Cell shrinks or plasmolysis occurs.

28. Facilitated Diffusion Transport protein that helps materials through the cell membrane. Doesn't require energy (ATP). Works on a downhill concentration gradient.

30. Active Transport Movement across membranes that DOES require cellular energy.

31. Types of Active Transport 1. Carrier-Mediated 2. Endocytosis 3. Exocytosis

32. Carrier-Mediated Transport General term for the active transport of materials into cells AGAINST the concentration gradient. Movement is: low high

33. Examples 1. Na+- K+ pump 2. Electrogenic or H+ pumps 3. Cotransport

34. Exocytosis Moves bulk material out of cells. Example - secretion of enzymes.

35. Endocytosis Moves bulk materials into cells. Several types known.

36. Types 1. Pinocytosis - liquids 2. Phagocytosis - solids 3. Receptor Mediated - uses receptors to "catch" specific kinds of molecules.