1. Cellular Membrane and Transport
GT Biology

2. Cell Membrane & Transport Introduction
In order to live, a cell must take in nutrients and water and eliminate wastes
Parts of the cell involved in diffusion and osmosis:
1. The cytoplasm
2. The cell membrane

3. 1. Cytoplasm – the jelly-like substance composed of mainly water and dissolved solutes. It is the matrix which contains all of the cellular organelles enclosed by the cell membrane.

4. 2. Cell membrane – a semipermeable membrane that allows some small molecules through, but blocks others.

5. Structure and Function of The Cell Membrane
Protect animal cells; the outer most layer
2. Control the movement of substances into and out of the cell
3. Contains molecules for cell identity and recognition

6. Structure
1. Phospholipids- Molecules that are made of a phosphate group and two fatty acid (lipid) chains.
* Phophate is the “head” and is polar or
hydrophillic (likes water)

7. Two fatty acid chains attached to the
phosphate groups they are the “tail”
and are hydrophobic (water hating)

8. These two molecules align side by side with the phosphates oriented toward the outside and inside of the and the lipids toward each other. WHY?
Phosphates are attracted to water
and lipids to other lipids

9. Outside cell
Phosphate heads
water
No water
Lipid tails
water
Phosphates heads
Inside cell

10. Selective Permeability animation

11. This forms the BILAYER ( double layer)
all the way around the cell.

12. 2. Cholesterol
Lipid molecules needed to keep the
bilayer rigid yet stable.

13. 3. Proteins
Proteins imbedded in the
membrane for various functions:
* enzymes ( catalyst for reactions)
* transport channels ( to allow substances
to cross)
*receptors (attachment of various
molecules that may enter the cell or
initiate a reaction)
* Protiens with carbohydrates attached
for Cell and self identification

15. The structure of the cell membrane has a special name…..
The Fluid- Mosaic Model
Why?
Fluid = fluid-like movement, maleable
like a water balloon, not like a ping-
pong ball.
Mosaic= a combination of many shapes
and sizes of molecules like an art
mosaic.

16. Cell membrane structure animation

17. Journal Entry Explain how the cell membrane
came to be a “Bi-layer”. In your
paragraph, explain what “bilayer”
means.

18. The movement of Various Substances Into and Out of Cells
Substances move into and out of the cell by
means of several methods. Some methods
require cellular energy while others do not.
A. Passive transport: no energy required
B. Active Transport: energy required

19. A. Passive Transport
1. Diffusion is the movement of molecules from an area of greater concentration to an area of lesser concentration. ( with the “flow”)
*Diffusion stops when equilibrium (balance) is reached

20. Low concentration
High concentration

21. Diffusion causes the molecules to move from area A to area B
( allows some things to move across…some
are too large and can’t pass through)

22. Diffusion causes the molecules to move from an area of high concentration to an area of low concentration until all are spread out equally… dynamic equilibrium

23. Diffusion/Osmosis animation
Protein Channels

24. 2. Osmosis is the diffusion of water across the cell membrane.
* The water will move from an area of low solute to an area of high solute until equilibrium is reached. (The water wants to evenly dilute the solute)

25. In osmosis, the water will move towards the solute to dilute it evenly.

26. Osmosis

27. 3. Diffusion and Osmosis Types of solutions
Hypertonic – the concentration of solutes outside the cell is greater than it is inside.
1. Water will move outside the cell to dilute the higher concentration of solutes
2. The cell will shrink

28. Hypertonic Solution
15% salt
85% water
1% salt
99% water

29. Plant cell
The cell wall does not
move. The membrane
shrinks in and pulls
all cell parts in=
plasmolysis
Animal cell

31. Hypotonic – the concentration of solutes inside the cell is greater than it is outside
1. Water will move inside the cell to dilute the higher concentration of solutes
2. The cell will SWELL (unless the water is pumped out by a contractile vacuole) – if not it may burst which is called cytolysis

32. Hypotonic solution
1% salt
99 water
15% salt
85% water

33. Plant cell
Cell fills with water
and the wall will
be forced to push out=
turgid
Animal cell

34. The contractile vacuole in single celled organisms pumps out excess water so the cell does not burst
Animation

35. Isotonic – the concentration of solutes inside and outside the cell is the same
1. Water will not move
2. The cell will stay the same

36. Isotonic solution

37. 4. Facilitative diffusion
Diffusion where molecules must pass through a protein to get across the cell membrane. ( still movement from high concentration to low)

38. Facilitative Diffusion animation

39. B. Active Transport Transport of molecules against the
concentration gradient, from low
concentration to high…against the “flow”

40. Because movement is AGAINT the flow, the
cell must use energy ( ATP is the
abbreviation for chemical cellular energy)
ATP is used to “power” proteins to pump
molecules across, forcing them to go
Against the gradient.

41. Example: Sodium – Potassium Pump The cell wants to keep low sodium in
and high potassium in. It must utilize
active transport to pump sodium out
and potassium in to keep these levels.
Sodium-potassium pump animation

42. Journal Entry What would happen if you took your
goldfish (freshwater fish) to Ocean City for the summer and decided to let it go in the ocean? Explain in terms of osmosis, hypertonic, hypotonic and such.
2. You decide to take the baby shark you caught in Ocean City and put it in your swimming pool. Explain as above.
3. Compare active and passive transport using a Venn diagram.