1. 3.3 Cell Membrane
Key Concept: The cell membrane is a barrier that separates a cell from the external environment.
Michigan Standard: 2.5h- Explain the role of cell membranes as a highly selective barrier (diffusion, osmosis and active transport)

2. Cell membranes are composed of two phospholipid layers.
A. Cell membrane is made up of phospholipids (phosphorous + fats)

3. 1. a polar head and two non-polar tails (likes water) (dislikes water)
3.3 Cell Membrane
1. a polar head and two non-polar tails
(likes water) (dislikes water)
Draw this

4. Draw this on the left side of your paper
3.3 Cell Membrane
Draw this on the left side of your paper
This represents a very small portion of a cell membrane
a cell

5. 3.3 Cell Membrane
Remember a cell membrane is a 3-D structure that completely surrounds a cell (kind of like the skin of an apple)

6. B. Other molecules are embedded within the “bi-layer”
3.3 Cell Membrane
B. Other molecules are embedded within the “bi-layer”
1. Cholesterol- for strength
2. Proteins- for moving things in and out of the cell
3. Carbohydrates- for identification

7. C. The cell membrane has been described by a fluid mosaic model
1. “fluid”- pieces moves around (like a soap bubble)
2. “mosaic”- made of many pieces

8. D. The cell membrane has the property of selective permeability
1. allows some, but not all materials to move through it
2. semipermeable or selectively permeable mean the same thing
example: waterproof clothing, a window screen

9. 3.3 Cell Membrane SKIP THIS
II. Chemical signals are transmitted across the cell membrane
A. Receptors help cells communicate and also help to move moleculues
1. receptor- a protein that detects a signal molecule and performs an action in response
2. “lock and key”
B. Receptors are usually very specific and only react to certain molecules
SKIP THIS

10. 3.4 Diffusion and Osmosis
Key Concept: Materials move across membranes because of concentration differences.
Michigan Standard: 2.5h- Explain the role of cell membranes as a highly selective barrier (diffusion, osmosis and active transport)

11. 3.4 Diffusion and Osmosis
Diffusion and Osmosis are types of passive transport.
Passive transport- the movement of molecules across a cell membrane without energy input from the cell
Diffusion- movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration

12. 3.4 Diffusion and Osmosis
C. Concentration- number of molecules of a substances in a given volume (space/ area)
High or Low?
High
High or Low?
Low

13. 3.4 Diffusion and Osmosis
D. concentration gradient- difference in concentration of a substance from one location to another
1. molecules diffuse down their concentration gradient
2. High concentration
Low concentration

14. 3.4 Diffusion and Osmosis High Concentration Equal Concentration
Low Concentration + + + + + + + + + + + + + + + + + + + + + + + + + + +

15. 3.4 Diffusion and Osmosis
E. Equilibrium- equal concentrations in all areas

16. 3.4 Diffusion and Osmosis
F. Osmosis- diffusion of water molecules across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration
Remember- the cell membrane is a semipermeable membrane (it lets certain things through it and keeps other things out)

17. 3.4 Diffusion and Osmosis This is a solution. Remember-
Solvent + Solute= Solution
Solvent is water
Solute is salt

18. 3.4 Diffusion and Osmosis
Which one has a greater concentration of solutes (salt)?
Low solutes
High solutes
vs.

19. 3.4 Diffusion and Osmosis
Which one has a greater concentration of solvent (water)?
Low solutes
High solutes
High water
Low water
vs.

20. 3.4 Diffusion and Osmosis F. There are three types of solutions
Hypertonic solutions
Hypotonic solutions
Isotonic solutions

21. 3.4 Diffusion and Osmosis
1. Hypertonic solution- has a higher concentration of solutes (dissolved particles) than a cell
Solution (outside of cell)
Inside of cell
Low concentration solutes
High concentration of water
High concentration solutes
Low concentration of water

22. 3.4 Diffusion and Osmosis
2. Hypotonic solution- has a lower concentration of solutes (dissolved particles) than a cell
Solution (outside of cell)
Inside of cell
high concentration solutes
low concentration of water
low concentration solutes
high concentration of water

23. 3.4 Diffusion and Osmosis
3. Isotonic solution- has the same concentration of solutes (dissolved particles) as a cell
Solution (outside of cell)
Inside of cell
equal concentration solutes
equal concentration of water
equal concentration solutes
equal concentration of water

24. 3.4 Diffusion and Osmosis
So, what’s going to happen?
Osmosis!!

25. 3.4 Diffusion and Osmosis Hypertonic Solution
But first, this cell is in what kind of a solution?
Hypertonic Solution
High solutes
outside
Low solutes
inside
Low water
outside
High water
inside

26. 3.4 Diffusion and Osmosis
Remember water moves from areas of high water concentration to areas of low water concentration
How will osmosis happen?
Will water move into the cell or out of the cell?
Out of the Cell!!
The cell shrinks!
Low water
outside
High water
inside

27. 3.4 Diffusion and Osmosis Hypotonic Solution
Now, what kind of solution is this cell in?
Hypotonic Solution
High solutes inside
Low solutes outside
High water outside
Low water inside

28. 3.4 Diffusion and Osmosis Hypotonic Solution Into the cell!!
Will water go into this cell or out of the cell?
Hypotonic Solution
Into the cell!!
The cell expands!
High water outside
Low water inside

29. 3.4 Diffusion and Osmosis Isotonic Solution
Now, what kind of solution is this cell in?
Isotonic Solution
Equal water and solutes inside and outside

30. The cell remains the same size.
3.4 Diffusion and Osmosis
Will water go into this cell or out of the cell?
Isotonic Solution
Both!!
The cell remains the same size.
Equal water and solutes inside and outside

31. 3.4 Diffusion and Osmosis
II. Some molecules diffuse through transport proteins.
Some molecules cannot slip through the cell membrane very easily.
Facilitated diffusion- the diffusion of molecules across a membrane through transport proteins

32. 3.4 Diffusion and Osmosis
B. Facilitated diffusion- the diffusion of molecules across a membrane through transport proteins

33. 3.4 Diffusion and Osmosis No Enery Needed Movement of Molecules
Passive Transport
Active Transport
Diffusion
Section 3.5
Osmosis
Facilitated Diffusion
No Enery Needed

34. 3.5 Active Transport, Endocytosis, and Exocytosis
Key Concept: Cells use energy to transport materials that cannot diffuse across a membrane.

35. 3.5 Active Transport, Endocytosis, and Exocytosis
I. Proteins can transport materials against a concentration gradient.
A. Active transport drives molecules across a membrane from a region of lower concentration to a region of high concentration.
High Concentration
Low Concentration

36. 3.5 Active Transport, Endocytosis, and Exocytosis
A protein uses energy to move molecules against the concentration gradient.
High Concon.
Low Concon.

37. 3.5 Active Transport, Endocytosis, and Exocytosis
II. Endocytosis and exocytosis transport materials across the membrane in vesicles.
A. Sometimes a cell needs to move big molecules into or out of a cell with a vesicle.

38. 3.5 Active Transport, Endocytosis, and Exocytosis
B. Endocytosis- the process of taking liquids or fairly large molecules into a cell by engulfing them in a membrane.
The cell membrane folds and a pocket is created
The pocket pinches off and a vesicle is created
The vesicle and its contents are broken down

39. 3.5 Active Transport, Endocytosis, and Exocytosis
C. Phagocytosis- a type of endocytosis in which the cell membrane engulfs large particles. “cell eating”
1. Very important process to fighting infection!

40. 3.5 Active Transport, Endocytosis, and Exocytosis
D. Exocytosis- the process of releasing substances out of a cell by the fusion of a vesicle with the cell membrane.
A vesicle is created around what needs to be removed
The vesicle moves to the cell membrane
The vesicle fuses with the cell membrane and releases the contents

41. 3.5 Active Transport, Endocytosis, and Exocytosis