1. Two major ways that molecules enter & exit cells
Diffusion & Osmosis
Two major ways that molecules enter & exit cells

2. Diffusion & Osmosis
Write this down and answer it after paying close attention to this lecture:
Explain why the following things occur using what you learn about osmosis and diffusion:
- Blood cells in pure water would absorb water and eventually burst!
- Blood cells in salty water would shrivel.

3. Diffusion
Movement of particles from areas of higher concentration to areas of lower concentration
Occurs spontaneously – requires no energy from the cell
Movement is driven by the kinetic energy (KE) of the particles
All particles have KE; KE increases as temp. increases

4. Example: A chamber is filled with two gases, one from the left & one from the right. What will happen over time?
= gas molecule

5. Molecules will diffuse due to their own KE & become evenly distributed
= gas molecule

6. In cells, small molecules (O2, CO2, etc
In cells, small molecules (O2, CO2, etc.) will diffuse across a membrane from areas of high concentration to low concentration

7. (High concentration of molecules) (Low concentration of molecules)
Example:
(High concentration of molecules)
(Low concentration of molecules)

8. Transport protein
Larger molecules will also diffuse but may require the help of a transport protein

9. Osmosis A specific type of diffusion
Refers to water diffusing across a semi-permeable membrane

10. Water molecules
Solute molecules (non-water)
In this scenario, more water will move to the right than to the left. Why?
The concentration of water molecules is greater on the left, and they will move from higher concentration to lower concentration

11. Example:
Semi-permeable
membrane (only water can move across)
Ask yourself:
1. Which side has a greater concentration of water molecules?
Water + Sugar
Pure water A B
Side B

12. membrane (only water can move across)
Example:
Semi-permeable
membrane (only water can move across)
Ask yourself:
2. Which side will have more water molecules colliding with the membrane?
Water + Sugar
Pure water A B
Side B

13. membrane (only water can move across)
Example:
Semi-permeable
membrane (only water can move across)
Ask yourself:
3. Which side will have more water molecules moving across the membrane?
Water + Sugar
Pure water A B
Side B

14. The net (overall) movement of water will be greater from B to A
Example:
Semi-permeable
membrane
Water + Sugar
Pure water A B
The net (overall) movement of water will be greater from B to A

15. AFTER:
Water + Sugar
Pure water A B
Eventually, equilibrium is reached where amount of water moving across is equal

17. Ask yourself: Cell The cell Cell Example:
1. Which side has a greater concentration of water molecules?
Saturated Salt Solution
Cell
The cell
Cell membrane

18. Saturated Salt Solution
Cell Example:
Ask yourself:
1. Which side will have more water molecules colliding with the membrane?
Saturated Salt Solution
Cell
The cell
Cell membrane

19. Saturated Salt Solution
Cell Example:
Ask yourself:
3. Which side will have more water molecules moving across the membrane?
Saturated Salt Solution
Cell
The cell
Cell membrane

20. The net (overall) movement of water will be out of the cell.
Cell Example:
Saturated Salt Solution
Cell
The net (overall) movement of water will be out of the cell.

21. Saturated Salt Solution
After:
Saturated Salt Solution
Cell
The cell will shrink as it loses water until water movement reaches equilibrium.

22. Also:
Saturated Salt Solution
Cell
The salt water is now more dilute while the cell is less watery.

23. What do you think would happen to blood cells in
pure water?
concentrated salt solution?

24. Blood cells in pure water would absorb water and eventually burst!
Blood cells in conc. salt solution would shrivel

25. In plant cells, the cell wall keeps the cell from exploding in pure water.