1. Homeostasis: Movement Across the Cell Membrane Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.

2. A. Cell Membrane  Cell Membranes surround ALL cells!  Controls what molecules enter and leave the cell - food & oxygen molecules must enter the cell - waste products need to be released  SEMIPERMEABLE – it allows some things through but not others

3. Structure of Cell Membrane  Phospholipid bilayer  Polar heads “love” water (hydrophilic)  Nonpolar tails “fear” water (hydrophobic)

4. C. Fluid Mosaic Model  Describes the various molecules found in the cell membrane  Example: -Proteins: forms channels and pumps to move materials across membranes - Carbohydrates: act like identification cards so cells can identify one another

6. D. Transport Across a Membrane  Molecules can enter/leave the cell in 2 ways: 1. Passive Transport * Simple Diffusion * Carrier-Facilitated (“helped”) Diffusion * Osmosis 2. Active transport * Protein Pump * Endocytosis * Exocytosis

7. Passive Transport  Energy is not required for movement across the membrane to occur  Molecules move from area of high concentration to area of low concentration  Example: Like riding a bike downhill

8.  Two factors determine if passive transport takes place, equilibrium and permeability - Equilibrium: when the concentrations on both sides of the membrane are equal membrane

9.  - Permeability: ability of a molecule to diffuse (move) across a membrane * Impermeable: molecules that cannot pass across a membrane * semi-permeable/selective permeability: Some molecules can pass across the membrane while other molecules cannot

10. higher conc. lower conc. Cell membrane A. Diffusion Diffusion  Molecules moving from area of high concentration to area of low concentration  No energy is required  Occurs because molecules constantly move and collide with each other *Click link

11. B. Carrier-Facilitated DiffusionCarrier-Facilitated Diffusion  No energy required  Molecules “helped” across by carrier proteins from high to low concentration Video (click here)

12. C. OsmosisOsmosis  Osmosis is a special type of diffusion  The diffusion of water molecules through a selectively permeable membrane *Click pic

13. ISOTONIC  Concentration of solutes (dissolved substance) is the same in and out of the cell  Equal amount of water leaving and entering cell HYPERTONIC  Solution has a higher solute concentration than the inside of cell  More water leaves cell, causing cell to shrink HYPOTONIC  Solution has a lower solute concentration than the inside of cell  More water enters cell, causing cell to expand (get big) *Click pic

14. Active TransPort  Energy required for molecules to pass across ◦ ATP – the “battery” of the cell ◦ Breaking a bond in ATP releases energy ◦ Can “pump” molecules from low to high concentration (against concentration gradient)  Example: Like riding a bike uphill ATP

15. A. Protein PumpProtein Pump ◦ Protein Pumps: pulls molecule through ◦ ATP Energy is required *Click Pic

16. B. Endocytosis Endocytosis  Endocytosis: cell membrane engulfs the larger molecule bring it into the cell  Two types: ◦ Phagocytosis: cytoplasm surrounds a molecule and packages it in a food vacuole ◦ Pinocytosis: cell membrane forms pockets filled with liquid and pinch off to form vacuoles in a cell

19. C. Exocytosis  Exocytosis: The membrane of the vacuole surrounding the material fuses with the cell membrane, releasing the material outside the cell *Click Pic