Cell Membrane Diffusion & Osmosis Active Transport, Endocytosis, & Exocytosis

1. Cell MembraneDiffusion & OsmosisActive Transport, Endocytosis, & Exocytosis Sections 3.3, 3.4, & 3.5

2. 3.3 Cell Membrane • Key Concept: • The cell membrane is a barrier that separates a cell from the external environment.

3. Cell membranes are composed of two phospholipid layers. • The cell membrane has two major functions • Forms a boundary between inside and outside of the cell • Controls passage of materials

4. Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer. • There are other molecules embedded in the membrane. • The fluid mosaic model describes the membrane.

5. Phospholipid Bilayer • Forms a double layer surrounding a cell • Composed of a charged phosphate group, glycerol, and two fatty acid chains • Head is polar (attracted to water) and forms hydrogen bonds with water • Tails are nonpolar (repelled by water)

6. Other Molecules in the Membrane • Cholesterol: strengthens membranes • Proteins: aid cell identification, movement of molecules across membranes, & cell signaling • Carbohydrates: aid cell identification

7. Fluid Mosaic Model of the Cell Membrane • Describes the arrangement of molecules making up a cell membrane • The membrane is flexible like a fluid • The membrane has a variety of molecules like the variety of tiles in a mosaic

9. Selective Permeability • Allows some materials to cross the membrane but not all • Enables cell to maintain homeostasis • Homeostasis: ability to maintain internal stable conditions • Molecules can cross in a variety of ways • Other terms: semipermeable & selectively permeable

10. Receptors • Detect a signal molecule and perform an action in response • Two Types: • Intracellular: located inside a cell; bind to molecules that can cross the membrane • Membrane: located in the membrane; binds to molecules that cannot cross the membrane; change in shape transmits the message to the cell interior

11. 3.4 Diffusion & Osmosis • Key Concept: • Materials move across membranes because of concentration differences.

12. Passive transport does not require energy (ATP) input from a cell. • Molecules can move across the cell membrane through passive transport. • Two types of passive transport: • Diffusion: movement of molecules from high to low concentration • Osmosis: diffusion of water

13. Diffusion and osmosis are types of passive transport. • Molecules diffuse down a concentration gradient. • High to low concentration

14. How do different solutions affect cells? • There are 3 types of solutions: • Isotonic: solution has the same concentration of solutes as the cell. • Water moves in and out evenly • Cell size stays constant

15. How do different solutions affect cells? • There are 3 types of solutions: • Hypertonic: solution has more solutes than a cell • More water exits the cell than enters • Cell shrivels or dies

16. How do different solutions affect cells? • There are 3 types of solutions: • Hypotonic: solution has fewer solutes than a cell • More water enters the cell than exits • Cell expands or bursts