1. Homeostasis & Transport
Chapter 8

2. Passive Transport
Section 8.1

3. Homeostasis?
How do cell membranes help maintain homeostasis within a cell?
By controlling what goes into and out of the cell.

4. Passive Transport
The movement of materials across a cell membrane WITHOUT the use of energy (ATP).
Four Types:
Diffusion
Osmosis
Facilitated Diffusion
Ion Channels

5. Diffusion
Movement of molecules from an area of high concentration to an area of low concentration.

6. Diffusion through a Membrane
Cell membrane
Solute moves DOWN concentration gradient
(HIGH to LOW)

7. Concentration Gradient
Difference in concentration of molecules across a space (or cell membrane).
“Down the gradient”
Movement from high to low concentration

8. Equilibrium
When the concentration is EQUAL throughout the space (or on each side of the cell membrane)
End of diffusion
No NET movement, RANDOM movement still occurs

9. Diffusion of Liquids

10. Diffusion across a membrane
Depends upon size, shape, and chemical makeup
Easy to diffuse:
Small
Nonpolar

11. Osmosis WATER diffusion across a membrane “Down the gradient”
Hypotonic solution to hypertonic solution
Osmosis
animation

12. Osmosis

13. Hypotonic Solution
The solute concentration is higher inside the cell, the water concentration is higher outside the cell.
Net movement = Water into the cell
May cause Cytolysis

14. Hypertonic Solution
The solute concentration is higher outside the cell, the water concentration is higher inside the cell.
Net movement = Water out of the cell
May cause Plasmolysis

15. Isotonic Solution
The solute and water concentrations are EQUAL on both sides of the membrane.
Equilibrium

17. Osmosis in Red Blood Cells
Isotonic
Hypotonic
Hypertonic

18. hypotonic
hypertonic
isotonic
hypertonic
isotonic
hypotonic

19. Facilitated Diffusion
Use of carrier proteins the assist diffusion across a membrane.
Specific carrier proteins for specific molecules (like glucose or amino acids)
“Down the gradient”

20. Diffusion via ion channels
Use of membrane proteins to assist diffusion of ions across a membrane
Channel is usually specific to 1 type of ion
Common ions:
Sodium
Potassium
Chlorine
Calcium

21. Notebook Quiz Osmosis is the diffusion of _____________.
During diffusion, molecules tend to move in what direction?
Does the movement of molecules stop once equilibrium is reached? Explain.
What is the function of carrier proteins?
If the external solution is hypotonic compared to the cell, which direction will water move?

22. Active Transport
Section 8.1

23. Active Transport
Uses energy (ATP) to move materials against the gradient
“Up the gradient”
Low to high concentration

24. 1. Sodium Potassium Pump
Transports sodium and potassium ions across the membrane up their gradients
Low to high concentration
Uses ATP

25. 2. Endocytosis Movement of large amounts of material into the cell
Formation of a vesicle from the cell membrane that will go to the lysosome for digestion
Uses ATP

26. 2 types of endocytosis 1. pinocytosis: “cell drinking”
Transport of a large quantity of liquid into the cell
2. phagocytosis: “cell eating”
Transport of a large quantity of solids into the cell
Uses ATP

27. Moving the “Big Stuff”
Large molecules move materials into the cell by one of three forms of endocytosis.

28. 3. Exocytosis
The movement of a large amount of materials out of the cell
Vesicle fuses to the cell membrane to release contents out of the cell
Uses ATP

29. Exocytosis
Exocytic vesicle immediately after fusion with plasma membrane.

30. Passive & Active Transport
Animation