1. Cells: Diffusion and Osmosis

2. Cells have to control what leaves and what enters the cytoplasm.

3. Water and solutes move according to the difference in concentrations
EVERYTHING naturally moves away from where it is highly concentrated and towards where it is less concentrated
This natural movement is called diffusion.
Diffusion takes place until the concentration reaches equilibrium (equal concentrations inside and outside of the cell).

4. The farther you move from a source, the lower the concentration
Distance from source
The farther you move from a source, the lower the concentration

5. Diffusion naturally tries to equalize concentration of water and solutes

6. Animal Cell Example
Carbon dioxide naturally diffuses out of animal cells because animal cells produce CO2 as they make energy from food.
The concentration inside is higher, so the net movement of CO2 is outward.

7. CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2

8. CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2

9. CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2

10. CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2

11. Oxygen naturally diffuses into animal cells because they use up oxygen as they turn food into energy
The concentration outside is higher, so the net movement of O2 is inward.

12. O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 O2

13. O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 O2

14. O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 O2

15. The cell membrane does not stop the diffusion of CO2, O2, or water molecules
This is because CO2, O2, and H2O are small molecules
These molecules will move across the membrane until equilibrium is reached.

16. Large molecules (like sugars) cannot get through the membrane, but water can.
Because of this, we call the membrane semipermeable.
A semipermeable membrane is selective about which molecules are allowed to pass
Small molecules are allowed
Large molecules (solutes) are not allowed.
The movement of water through a semipermeable membrane that blocks large molecules from moving is called osmosis.

17. high concentration of solute lower concentration of solute
= Solute (ex: sugar)
membrane
= water ↓
high concentration of solute
lower concentration of solute

18. high concentration of solute lower concentration of solute
= Sugar
= water
high concentration of solute
lower concentration of solute

19. high concentration of solute lower concentration of solute
= Sugar
= water
high concentration of solute
lower concentration of solute

20. high concentration of solute lower concentration of solute
= Sugar
= water
high concentration of solute
lower concentration of solute

21. The net flow of water is towards the higher solute concentration
high concentration of solute
lower concentration of solute

22. Osmosis is the diffusion of water through a semipermeable membrane
Osmosis is the diffusion of water through a semipermeable membrane. Water molecules move from areas of high concentration to areas of low concentration.

23. Osmosis can pull water into a cell if the cell is placed in an environment with a lower solute concentration

24. Hypotonic means lower solute concentration
animal cells can rupture in hypotonic environments
plant cells are protected from rupture by their strong cell walls

25. blood cell in hypotonic environment
normal blood cell
blood cell in hypotonic environment
blood cell ruptures due to water flooding inward

26. Osmosis can also pull water out of a cell if the cell is placed in an environment with a higher solute concentration

27. Hypertonic means higher concentration of solutes
A cell placed in a hypertonic environment will lose water and shrink.
Plant cells plasmolyze when placed in very salty water.

28. Egg placed in hypertonic syrup Egg placed in syrup after 24 hours
Osmosis dehydrated the egg.

29. chloroplasts Normal plant cell Plant cell placed in hypertonic
cell wall
cell
membrane
Plant cell placed in hypertonic
environment causes water to move outward
Plasmolyzed plant cell “drained” of water by osmosis
Normal plant cell

30. Isotonic means balanced
Cells in an isotonic environment experience no net flow of water due to osmosis.
The water flowing in is balanced by the water flowing out

31. Summary Hypertonic = higher = dehydrating environment, cells shrink
Hypotonic = lower = bloating environment, cells swell
Isotonic = equal =homeostatic environment, cells “happy”