1. Cell Boundaries
September 8th, 2008

2. The Cell Membrane
The cell membrane regulates what enters and leaves the cell and also provides protection and support.
The cell membrane is made up of a lipid bilayer, meaning two layers of lipids (fats).

3. The Cell Membrane
The heads of the lipids are HYDROPHILIC, meaning “water loving”.
The tails of the lipids are turned inward, facing one another because they are HYDROPHOBIC, meaning “water fearing”.
Hydrophilic
Heads
Hydrophobic
Heads

4. The Cell Membrane
In addition to lipids, most cell membranes contain protein molecules that act as pathways for materials to move through the cell.
Finally, carbohydrates are attached to many of these proteins, and act like chemical identification cards, that allow cells to identify one another.

5. Membrane Structure Outside Carbohydrate Chains of Cell Cell Membrane
Lipid Bilayer
Inside
of Cell
(Cytoplasm)
Protein
Channel

6. Diffusion Through Cell Boundaries
Recall that the major role of the cell membrane is to regulate what enters and leaves the cell.
Sometimes, substances move back and forth through the cell membrane freely.
This process is called DIFFUSION.
Diffusion DOES NOT require the cell to use energy.

7. In the process of diffusion, particles (also called solutes) move back and forth through the cell membrane until there is an equal number on both sides of the membrane. This is called EQUILLIBRIUM.
Before
After
Solute
Particles
Cell Membrane

8. Reflection What is the main function of the cell membrane?
What does it mean that a cell membrane has a “lipid bilayer”?
True or False: Diffusion requires the cell to use energy to move solute back and forth through the membrane?
What does it mean for a solution to have reached equilibrium?

9. The Cell Membrane and Osmosis
9/10/08

10. Osmosis
Water passes quite easily across most membranes, even though many solute molecules can not. This process is known as osmosis.
OSMOSIS is the diffusion of water through a selectively permeable membrane.

11. Osmosis
Water will tend to move across the membrane until equilibrium is reached. At that point, the concentrations of water and salt will be the same on both sides of the membrane.

12. Osmosis Solution Animal Cell Plant Cell
Isotonic – the concentration of solutes is the same inside and outside of the cell.
Hypertonic – Solution has a higher solute concentration than the cell.
Hypotonic – Solution has a lower solute concentration than the cell.

13. Reflection Explain what “selectively permeable” means.
What is osmosis?
What is the difference between Hypertonic and Hypotonic?
Why doesn’t a cell’s appearance change when it is placed in an isotonic solution?

15. Facilitated diffusion and Active Transport.
September 11th, 2008

16. Facilitated Diffusion
In facilitated diffusion, molecules such as sugar and proteins move across the cell membrane with the help of a carrier protein.

17. Just as in regular (simple) diffusion, molecules move from an area of higher concentration, to an area of lower concentration, until equilibrium is reached.
However, each different type of molecule requires a different carrier protein to take it across the membrane.

18. Even though proteins are necessary to move things across the membrane, facilitated diffusion does NOT require the cell to use any energy.
(Click picture to the right to view video)

19. White Board Wars - Reflection
Facilitated diffusion requires
enzymes.
carrier Proteins.
lipid carriers.
carbohydrate carriers.
lipid or carbohydrate carriers.

20. Facilitated diffusion is used to transport
sugars and amino acids.
H2O and O2.
CO2 and O2.
CO2 and H2O.
sugars and H2O.

21. Facilitated diffusion is used to transport
sugars and amino acids.
H2O and O2.
CO2 and O2.
CO2 and H2O.
sugars and H2O.

22. Unlike simple diffusion, facilitated diffusion requires energy expenditure by the cell.
True
False

23. Facilitated diffusion requires a specific transporter for a specific molecule.
True
False

24. Active Transport
Active transport is a process that moves molecules, such as calcium, potassium, and sodium, across the cell membrane against their concentration gradient (from an area of low concentration to an area of high concentration).

25. The process uses a carrier protein just like facilitated diffusion, however active transport REQUIRES energy (from ATP) in order for the pump to work.
(RealPlayer Video: Active Transport)

26. Endocytosis and Exocytosis
Larger molecules and even solid clumps of material that are too big to diffuse across the membrane or move through a carrier protein, may be transported by movements of the cell membrane.
Examples of this are the processes known as Endocytosis and Exocytosis.

27. Endocytosis
Endocytosis is the process of a cell taking in material (such as food) by in-folding, or making a pocket (vacuole) out of, the cell membrane.

28. Two examples of endocytosis are
Phagocytosis – when the cell engulfs (takes in) food particles to be digested (eaten).
Pinocytosis – when the cell engulfs (takes in) liquid from outside the cell.

29. Exocytosis
Exocytosis is when the membrane of the vacuole surrounding the material, fuses with the cell membrane, forcing the contents of the vacuole out of the cell.
Cell
Membrane 4 3 2 1
Golgi Apparatus
(RealPlayer Videos: Endocytosis and Cell Membrane, Endocytosis, and Exocytosis)

30. White Board Wars - Reflection
Which of the following is an example of active transport
Facilitated diffusion
Osmosis
Diffusion
Endocytosis
None of the above

31. Which process always involves the movement of materials from inside the cell to outside the cell?
Phagocytosis
Endocytosis
Diffusion
Exocytosis
Pinocytosis

32. Active transport requires the cell to use energy to move materials in and out of the cell.
True
False

33. Energy is required to move materials into the cell during endocytosis, but not required to move materials out of the cell during exocytosis.
True
False

34. Review: Passive Transport vs. Active Transport
Movement of molecules from an area of high concentration to low concentration.
Molecules move until they reach equilibrium.
Does NOT require the cell to use energy.

35. Examples
Diffusion – the movement of solute (particles) through the cell membrane from an area of high concentration to an area of low concentration.
Osmosis – the movement of water through the cell membrane from an area where there is a low concentration of solute to an area where there is a high concentration of solute.
Facilitated Diffusion – the movement of specific molecules across a cell membrane through protein channels, from an area of high concentration to an area of low concentration.

36. Active Transport
Movement of molecules across the cell membrane from an area of low concentration to high concentration.
Or, the movement of molecule across the cell membrane that are too large to diffuse through or be carried by proteins.
Requires the cell to use energy.

37. Examples
Active Transport – the process that moves molecules across the cell membrane against their concentration gradient (from an area of low concentration to an area of high concentration).
Endocytosis – the process of a cell taking in material (such as food or liquid) by in-folding, or making a pocket (vacuole) out of, the cell membrane.
Exocytosis – when the membrane of the vacuole surrounding the material, fuses with the cell membrane, forcing the contents of the vacuole out of the cell.