2. Cell Membrane Controls what materials enter or leave the cell Also called the phospholipid bilayer Heads are hydrophilic(“water loving”) They attract water Tails are hydrophobic (“water fearing”) They repel water Have protein channels to allow larger substances to enter/leave the cell

3. Cell Membrane

4. Diffusion Particles in a solution move along the concentration gradient Concentration gradient – particles of a solution move from areas of high concentration to low concentration Uses NO ENERGY!

6. Osmosis The diffusion of water across a semipermeable membrane Goes from high concentration to low concentration The plasma (cell) membrane undergoes osmosis creating equilibrium in the cell Equilibrium is reached when both sides of the cell membrane are equal

7. 3 Types of Osmotic Solutions Isotonic: Equal movement of water molecules across a selectively permeable membrane, no net change in the cell

9. 3 Types of Osmotic Solutions Hypotonic: Water enters the cell across a selectively permeable membrane to dilute the concentration of macromolecules inside the cell. Causes the cell to swell

11. 3 Types of Osmotic Solutions Hypertonic: movement of water out of the cell through the selectively permeable membrane causes the cell to shrink

13. Active Transport Active transport: movement of materials through a membrane from low concentration to high concentration Going against the concentration gradient Requires ENERGY!