1. Chapter 7 Cell Structure and Function
Section 7.3- Cell Boundaries
Objectives:
Identify the main functions of the cell membrane and the cell wall.
Describe what happens during diffusion.
Explain the process of osmosis, facilitated diffusion, and active transport.

2. Cell Membrane
Cell membrane
Border
Phospholipid bilayer

3. Cell Membrane Fluid Mosaic Model Proteins embedded in lipid bilayer
Cell surface markers, pumps, channels, receptors

4. Cell Wall
rigid layer
made of cellulose

5. Passive Transport What does passive mean? What does transport mean?
Movement of substances across a membrane “down” their concentration gradients without using energy

6. Diffusion Net flow from high conc. to low conc.
Driven by kinetic energy (energy of motion)

7. Diffusion Semipermeable Membrane Down Concentration Gradient
Equilibrium
“both sides are equal”
High [ ]
Low [ ]

8. Osmosis Diffusion of water across a membrane
Direction of osmosis into or out of a cell depends on solute concentrations inside and outside the cell
Animation of Osmosis

9. Osmosis- Direction of Osmosis
Isotonic
Hypertonic
Hypotonic
Salt is the solute
A solute is a substance that dissolves in a solvent

10. Facilitated Diffusion
Diffusion that requires the help of carrier proteins
Animation of Facilitated Diffusion

11. Diffusion Through Ion Channels
Ion channels are membrane proteins that allow only specific ions to pass through.
Channels can be “open” or “gated”
If an ion channel is gated, it can be opened by stretching the cell membrane, a voltage, or a chemical

12. Active Transport
Cell Membrane Pumps
Movement in Vesicles

13. Active Transport What does active mean? What does transport mean?
Movement of substances across a membrane “up” their concentration gradients using energy

14. Cell Membrane Pumps ATP
Carrier proteins that move substances from areas of low concentration to areas of high concentration.
Requires energy
What molecule furnishes the energy to power the pump?
ATP

15. Sodium-Potassium Pump
Transports Na+ and K+
3 Na+ out of cell / 2 K+ into cell

16. Animation of Sodium-Potassium Pump
How Na+/K+ pump works:
Animation of Sodium-Potassium Pump

17. Movement in Vesicles
What happens if substances are too large to pass through the cell membrane or carrier protein?
What does the prefix endo- mean?
What does the prefix exo- mean?
What does cyto- mean?
What does –osis mean?

18. Movement in Vesicles Endocytosis
Process by which cells ingest what they need.
Requires energy
Cell membrane folds and pinches off to form a vesicle

19. Endocytosis 2 Types Pinocytosis Phagocytosis
Endocytosis of solutes and fluids
Phagocytosis
Endocytosis of large particles and whole cells
Phagocytes

20. Movement in Vesicles Exocytosis
Process by which cells release unwanted substances.
Requires energy
Vesicles fuse to membrane to let substances out of cell