Cell Unit Notes Lecture II

1. Cell Unit NotesLecture II Cell Biology Standards in Lecture II > 1a ~ students know cells are enclosed within semi permeable membranes that regulate their interactions with their surroundings

2. The Cell Membrane • The cell membrane regulates what enters and leaves the cell • It also provides support and protection • The cell takes in food and water and eliminates wastes through the cell membrane • The cell membrane is selectively permeable

3. Selective Permeability

4. The Lipid Bilayer • Most cell membranes are made up of a double-membrane layer called the lipid bilayer • Along with lipids the membrane also has proteins that are “stuck” in it (see below)

5. The Lipid Bilayer • Along with the proteins are “carbohydrate chains” that are attached to the protein • These “chains” act like an identification card or “face” so the cell can be recognized Carbohydrate chains Protein channel

6. Diffusion • All living cells are surrounded by and full of liquid • Even a cactus in the desert has moist cells in it’s living tissue • One of the most important functions of the cell membrane is to regulate the movement of molecules from one side of the membrane to the other

7. Diffusion • The concentration of a solution is the relative “purity” of a liquid • There can be a high concentration to a low concentration • A solution will move in the direction of high concentrationto low concentration and this is called Diffusion

8. Diffusion • Diffusion allows substances to cross the cell membrane without requiring the cell to use energy • This is very important since energy must be conserved – even at the cellular level!

9. Osmosis • Selective permeability means that only select “things” can pass through the membrane • Osmosis is “the diffusion of water across a selectively permeable membrane”

10. Osmotic Pressure • Isotonic – means that on both sides of the cell membrane it is the same “concentration” • Hypotonic – the cell fills up with water and is in danger of “bursting” • Hypertonic – the cell loses much of its water concentration and can “shrink” • (Animal Cells react differently than plant cells because of the cell wall that plant cells have)

11. Osmotic Pressure

12. Facilitated Diffusion • This is diffusion across the cell membranewith the “help” of proteins • It still flows from a high to low concentration

13. Facilitated Active and Passive Transport

14. Active Transport • Active transport requires “action” or energy in order to move these particles across the cell membrane • The input of energy along with special proteins on the surface of the cell can move any particles across any “gradient” • Gradient – relative concentration of a solution

15. Endocytosis & Exocytosis

16. Exocytosis • The removal of large amounts of material from the cell is known as exocytosis • The vesicle fuses with the cell membrane and forces its contents out of the cell