1. Diffusion, Osmosis, and Water

2. Diffusion is…
The net movement of particles from an area of high concentration to low concentration
Animation

3. Facilitated Diffusion

4. Diffusion is always passive!
No energy
is required

5. What about if we want to go against the gradient?
How does the train get up the hill?
Does it need energy to go back down?

6. Active Transport – going up the hill

7. Osmosis – What is it?
In diffusion, the particles of something move (sodium, sugar, etc.)
In osmosis, WATER particles move from an area of high WATER concentration to low WATER concentration across a membrane.

9. How can this happen? The structure of the plasma membrane
Hydrophobic tails
What is a “phobia”
What does “hydro” mean?
Hydrophilic head
If “phobia” = fear, what might “philia” mean?
Hydro-philic = “Water loving”

10. Some things can pass through the plasma membrane, some things can’t

11. Diffusion, including osmosis, helps maintain homeostasis

12. In osmosis, the state of dynamic equilibrium is “isotonic”
Note how the water and solute is spread out evenly between the inside and outside of the cell. This cell is in dynamic equilibrium. There will be no net water movement.

13. Cells can also be in hypotonic conditions
What other words contain “hypo”?
Hypo = “Less than”
There is LESS solute outside the cell than inside the cell
The solute particles can’t move, so water will move to balance things out.

14. HYPOtonic

15. Hypotonic Solution
Before osmosis…
… after osmosis

16. …After osmosis Water rushed into the cell, causing it to swell.
When placed into a hypotonic solution, an animal cell would probably burst, but a plant cell will not.
Why is a plant cell protected against bursting?

17. We put plants in hypotonic conditions all the time!

18. Lastly, cells can be in hypertonic conditions
When someone is hyper, do they have a lot of energy or a little energy?
Hyper = “a lot”, “excess”
Hypertonic solutions have a lot of solute compared to the cell (and relatively less water).

19. Hypertonic
Which way will the water go?

20. Water is truly amazing

21. Water is “polar”, which gives it special properties

22. Water is “sticky”
This happens through hydrogen bonding

23. Water looks like this…

24. NOT this…

25. Without this little bend, life as we know it would not exist

26. What special properties does water have?

27. Water has “surface tension”

28. Water is “cohesive”

29. Water is “adhesive”

30. Water is a great solvent

31. Let’s look at these properties in action!