1. Cell Membrane

2. Function Protects cell
Allows for passage of certain materials in and out of cell

3. Structure Double layer of phospholipids
Polar heads, nonpolar fatty acid tails
Proteins help materials move through
Carbohydrates attach to proteins for cell identification

4. Fluid Mosaic Model
Describes the arrangement of molecules making up the cell membrane
Based on two characteristics:
Flexibility- phospholipids move and slide past each other (fluid)
Appearance- variety of molecules scattered throughout membrane (mosaic)

5. Selective Permeability
Allows some (but not all) materials to cross
Important to maintain homeostasis within the cell
Passage through membrane varies, but in general:
Small nonpolar molecules easily pass through
Small polar molecules transported via proteins
Large molecules moved through in vesicles

6. Transport of Materials
Passive transport- passage of materials does not require energy
Diffusion
Osmosis
Facilitated diffusion
Active transport- requires energy
Endocytosis

7. Diffusion Movement of molecules from high to low concentration
Concentration gradient- difference in concentration of a substance throughout the solution
Dynamic equilibrium- concentration is uniform throughout solution (equilibrium), but molecules are always moving (dynamic)
Small lipids and other nonpolar molecules diffuse across

8. Osmosis Movement of water molecules from high to low concentration
Isotonic solution- same concentration of dissolved particles as cell
Hypertonic solution- has a higher concentration of dissolved particles than cell; cell shrivels
Hypotonic solution- lower concentration of dissolved particles than cell; cell expands and bursts

9. Facilitated Diffusion
Diffusion of molecules across the membrane through transport proteins
Still no energy required… passive transport

10. Active Transport
Requires energy to move molecules through cell membrane
Molecules move against concentration gradient (from low to high concentration)
Uses transport proteins
Span membrane
Use chemical energy (typically ATP) to move substance

11. Endocytosis
Process of taking in liquids/other large molecules by engulfing them in the cell membrane
The resulting vesicle then fuses with a lysosome to be broken down

12. Endocytosis Phagocytosis “cell eating” Pinocytosis “cell drinking”
Exocytosis- opposite of endocytosis
Release of substance out of cell