1. Chapter 13 Diffusion and osmosis

2. Syllabus Explain the role of selectively permeable membranes.
Define the terms: osmosis & diffusion
Give examples of diffusion and osmosis.
Define the term: turgor.
Explain turgidity in plant cells.
Describe the application of high salt or sugar concentration in food preservation.

3. The Cell

6. Cell membrane is the boundary between inside & outside… separates cell from its environment
Can it be an impenetrable boundary?
NO! IN
food
carbohydrates
sugars, proteins
amino acids
lipids
salts, O2, H2O
OUT
waste
ammonia
salts
CO2
H2O
products
OUT IN
cell needs materials in & products or waste out

7. Permeability Membranes can be Permeable – let everything in and out
Semi Permeable - let some things in and out
Impermeable – let nothing in and out

8. Homeostasis – Maintaining a Balance
Cells must keep the proper concentration of nutrients and water and eliminate wastes.
The plasma membrane is selectively permeable – it will allow some things to pass through, while blocking other things.

9. Diffusion and Osmosis Animations
View movement in the cell membrane, diffusion, osmosis
Video on Osmosos & Diffusion

10. Diffusion
movement of molecules from an area of high concentration to an area of low concentration.
Passive transport / no external energy needed.

11. Diffusion

12. Diffusion in everyday life
CO2 diffusing into a leaf
O2 diffusing out of a leaf
O2 diffusing into an animal cell
CO2 diffusing out of an animal cell

13. Learning check Name 3 different types of membranes.
Explain the term Homeostasis.
How does the membranes play a role in maintaining Homeostasis?
Explain the role of selectively permeable membranes.
Define Diffusion

14. Osmosis
is the movement of water from a region of high water concentration to a region of low water concentration across a semi-permeable membrane
Passive transport / no external energy needed.
Occurs until water is balanced on both sides of the membrane.

15. osmosis
movement of water

17. Learning Check
What is osmosis?
Does osmosis require energy?

18. OSMOSIS & Animal cells Animal cells in a solution that is the
same concentration as their Cytoplasm - stay the same size
less concentrated solution - gain water, swell and may burst
more concentrated solution - lose water, shrivel and may die

19. Osmosis in animal cells

20. Shrivelled Animal Cells

21. Overcoming Osmosis
Amoeba survives in a less concentrated (freshwater) environment due to its contractile vacuole, which eliminates water.

22. Learning check What surrounds an animal cell?
How does water move in and out of an animal cell?
What will happen to animal cells in a very dilute (watery) solution?
What will happen to animal cells in a very concentrated solution?

23. OSMOSIS & PLANT cells

24. Plant cells in a:
less concentrated solution than their cytoplasm - gain water and become turgid (swells) and strong.

25. Turgor pressure This turgor pressure gives plants their strength
If plants did not have this they would wilt
Plants that don’t have wood such as lettuce and house plants rely on turgor pressure for strength
Osmosis in the kitchen

26. Plant cells in a:
more concentrated solution - lose water and become plasmolysed (wilts) and weak.

28. Learning Check What surrounds the membrane of a plant cell?
Can this structure control what moves in and out of cells?
How does water enter roots of a plant?
What is meant by a turgid cell?
How could you identify a turgid cell?

29. Food Preservation
Bacteria and Fungi are the most common causes of food spoilage
If a food is placed in a high sugary or salty solution then any bacteria or fungi present, will lose the water in their cells by osmosis, shrivel and die.
E.g. Salting fish or high sugar concentration in jam.

30. Learning Check What is meant by plasmolysis?
What kind of a solution would you put plant cells in to cause them to palsmolyse?
How is plasmolysis used to preserve food?
Give an example of some types of food preserved in this way?

31. Annimation showing molecules moving in osmosis

32. Animation: Membrane How Osmosis work – animation + audio lesson
Animation: How Osmosis Works
Check out this Shockwave video of simple diffusion, facilitated diffusion, and osmosis. This is a great overview of these terms
Animation: Membrane

33. To show osmosis:
Place bags of visking tubing half-filled with
(a) distilled water,
(b) 80% sucrose solution,
in distilled water.
Bag (a) stays the same mass and size.
Bag (b) increases in mass and swells
as water enters
due to osmosis.

35. Osmosis Experiment
Fill each of the petri dishes about half full of water and place them on a table or flat surface where they can sit for several hours without being in the way.
Use the paper and pen to make a label for each bowl. One label should say "Plain Water", and one should say "Salt"
Next you want to add salt to the water in the bowl labeled "Salt."
Keep adding salt.
CAREFULLY slice the potato down the middle, lengthwise. You want there to me as much of the raw potato exposed as possible.
Place one potato half with the flat side down onto one dish, and the other half down on the other dish. Then, you wait. 
After 30 minutes, take the potato out of the bowls and examine them.
What do you see? 

37. Video on Pototoe Expt

39. Instructions on drowning-gummies-aka-gummy-bear-osmosis-experiment
Gummy Bear Video