1. Movement through cell membranes

2. Objectives You should be able to:
Define the term "diffusion” and give examples.

3. Diffusion
Diffusion is the spreading out of particles from a region of high concentration to a region of low concentration.
Diffusion moves down a concentration gradient.
It is a passive process – no energy input is required!
Only can happen over short distances

4. Diffusion animation 1

5. Diffusion animation 2

6. Diffusion in everyday life
Smell of perfume
Stink bomb
Sugar in tea 6

7. Example of diffusion in living things
In the alveoli oxygen diffuses from the alveoli to the blood capillaries and carbon dioxide diffuses out
Animation

8. Check your learning.. Define diffusion?
Why is diffusion called a passive process?
Give some examples of diffusion in everyday life
Give an example of diffusion in a living thing/

9. Objectives You should be able to:
Define the term “osmosis” and give examples.
Investigate osmosis

10. Permeability Membranes can be Permeable – let everything in and out
Semi Permeable - let only some substances in and out
Impermeable – let nothing in and out 10

11. Selective permeability of membranes
Cell membranes and organelle membranes are selectively permeable
Because the holes/ pores are not large enough, because of the charges on the cells etc.

12. Diffusion animation 3

13. Osmosis is a type of diffusion, so what do you think happens to water molecules during this process?
semipermeable membrane
Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration across a semipermeable membrane.

14. Osmosis animation 1

15. Osmosis animation 2

16. What is happening here?

18. To investigate osmosis
To be a fair test:
Use the same size beakers with equal amounts of water.
Equal lengths of visking tubing.
Volume of liquid in visking tubing equal.
Find the mass of each tube before you start and note it.
Leave them for the same amount of time.

19. To investigate osmosis
Results:
Remove the bags, dry them and record the mass of each bag.
Also note any changes in fullness of each bag.

20. Can you.. Explain what a semi permeable membrane is?
Tell what osmosis is?
Explain why osmosis is a special case of diffusion?

21. A bag made from a semipermeable membrane is tied
to a glass tube and filled with a strong sugar solution.
This bag is placed in a weak sugar solution.
strong sugar
solution
weak sugar
solution
What happens to the water molecules in the weak solution?
What happens to the liquid inside the semipermeable bag?

22. Today’s objectives By the end of today’s class you should be able to:
Describe what happens to plant cells in different types of solutions
Know what a cell with turgor is

23. If a plant cell is surrounded by a solution which has a higher water concentration:
Water from outside will flow into the cell by osmosis,
the vacuole becomes bigger and the cytoplasm swells
The cell membrane is pushed out towards the cell wall – the cell is called “Turgid”. 23

24. Lettuce leaves are crisp when the cells are turgid!
Turgor
Def Turgor Pressure is the pressure of the cytoplasm and the vacuole pushing against the cell wall of the plant. (Also called “turgor”)
Lettuce leaves are crisp when the cells are turgid!

25. If a plant cell is surrounded by solution which is less concentrated with water
the water inside the cell would move out by osmosis
the cell wall stays intact but the membrane shrivels up away from it 25

26. Wilting

27. See animations

28. Check your learning.. Define osmosis
What is a semi- permeable membrane?
What happens to a plant cell when it is put in a solution of higher water conc?
What is a cell like this called?
What would happen to an animal cell in a solution of higher water conc?
What happens to a plant cell when it is put in a solution of lower water conc?

29. Learning objectives
To learn about how osmosis is used to prevent food spoilage and 2 examples of this

30. Osmosis and Food Preservation
Bacteria are a most common causes of food spoilage
Bacterial cells have a cell membrane 30

31. If a food is placed in a sugary or salty solution then any bacteria present will lose the water in their cells to the solution outside
The bacteria cells shrivel and die!

32. Examples Fish and Meat (bacon) may be stored in a salty solution
Jams, marmalades and tinned fruits are stored in a sugary solution 32

33. Syllabus Can you?..... Define the term: Selectively permeable
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. 33