2. The Cell Membrane & Transport

3. The Cell Membrane  The cell membrane is a skin-like structure surrounding the cytoplasm serving as a barrier to the cell’s environment.  The Cell membrane functions as the Gatekeeper of the cell, transporting essential materials inside and out of the cell.

4. What does a cell need to transport? 1.Food in 2.Water in/out 3.Oxygen in 4.Waste like CO 2 out

5. Semi-Permeable  Because only certain things can move across the membrane it is said to be semi permeable

6.  The membrane only allows small, uncharged molecules to cross.  Can cross: Water, O 2, CO 2,  Cannot cross:  Large molecules like proteins or carbohydrates.  Charged ions like Cl -, Na +

7. Composition of the Cell Membrane  The cell membrane consists of: 1.phospholipid bilayer 2.proteins.  The phospholipid bilayer looks like:

8. Phospholipid Bilayer

9. Fluid Mosaic Model  The analogy of the membrane: proteins are like icebergs floating in the phospholipid ocean.

11. Concentration Gradient  Concentration gradient = the difference in concentration (amount of dissolved stuff) on both sides of the membrane.

12. Membrane Transport  There two main ways to move things across the membrane  Passive Transport  Active Transport

13. Membrane Transport  Passive Transport  Molecules move from an area of high concentration to low concentration  Requires No Energy Active Transport Molecules are moved from an area low concentration to high concentration Requires Energy

14. Passive Transport - High to Low No Energy Needed Active Transport - Low to High, Needs Energy

15. Passive Transportation  Two examples of passive transport:  Simple Diffusion  Facilitated Diffusion

16. Simple Diffusion  Simple Diffusion is when molecules move randomly from an area of high concentration to an area of lower concentration until they are evenly spread out (Dynamic Equilibrium)

17. Facilitated Diffusion  Some molecules need “help” to get across the membrane (Facilitate means to help)  Through Facilitated Diffusion, proteins in the membrane provide a pathway for certain molecules to pass from high to low concentration.

19. Active Transport  Some substances need to be moved from low to high concentrations, this is accomplished by active transport  Two examples of Active Transport:  Pumps  Bulk Transport

20. Pumps  Pumps involve carrier proteins and energy  Carrier proteins Pump molecules against a gradient from Low to high concentration with the use of energy.

21. Bulk Transport  Cells also use energy to move large amount of things into and out of the cell in bulk by folding the membrane around what needs to be moved  Cells bring in bulk items by endocytosis.  Cells remove bulk items from the cell by exocytosis

24. Membrane Transport Summary  There are three primary means that water and other small molecules cross into or out of cells.  Diffusion  Facilitated Diffusion  Active Transport  All play an important role in the regulation of body fluids and many other physiological functions. Passive Transport