The cell membrane regulates what enters and exits the cell through passive and active transport. Passive transport involves diffusion and facilitated diffusion, moving down concentration gradients without energy. Active transport uses protein pumps and requires energy to move molecules against concentration gradients, such as the sodium-potassium pump maintaining ion balance in animal cells. Membranes are semipermeable due to the phospholipid bilayer, which only allows small nonpolar molecules to pass through.

1. Membrane Transport
How molecules move through cell
membranes

2. • Where can you find membranes in a cell?
• What are the functions of the cell
membrane?
• What is a semipermeable membrane?

3. Membranes are found
around the cell and each organelle

5. • The cell boundary;
separates cellular
materials from
external environment
• Regulates which
materials can enter
and exit the cell
• Maintains
homeostasis in cell

6. Semipermeable membranes
• Membranes that allow certain materials to
pass through based on certain properties
– size
– hydrophobicity
– charge

7. The Fluid Mosaic Model: The membrane is
made up of many smaller parts and the
structure moves like a fluid
• http://www.susanahalpine.com/anim/Life/memb.htm

8. Phospholipids and proteins make up most of the
membrane. Cholesterol helps with flexibility, and
carbohydrate chains help communicate with other
cells

9. A phospholipid is a type of lipid that has
2 fatty acid tails and a phosphate head.
• http://telstar.ote.cmu.edu/Hughes/tuto
rial/cellmembranes/
The phosphate head is
hydrophilic
because it is attracted to
water
The fatty acid tails are
hydrophobic
Because they are repelled
by water
Use E-Life animation 6.3
https://www.youtube.com/watch?v=pzpZdijj
qX8

10. The phospholipid bilayer forms because the
inside and outside of the cell are mostly water:

11. A cell membrane has many properties
in common with bubbles!

12. Clean up:
• Pour soap down drain
• Rinse plate, straw frame and beaker
VERY well
• Throw out used straws and thread ring
• Return plate, straw frame and beaker
• Wipe down table top VERY well

13. The phospholipid bilayer is a
semipermeable membrane because it
only allows certain molecules to cross.

14. Hydrophilic, polar, large and charged
molecules must use a Transport Protein to
enter/exit the cell.
The proteins are specific; glucose can only
pass through a glucose transport protein.

15. There are two types of Transport Proteins:
Protein Channels: a special entryway for
large, polar, hydrophilic and charged ions to
diffuse through the cell membrane
This is called Facilitated Diffusion.
Protein Pumps: we’ll talk about these later

16. The Big Idea
1. Name 4 components of the cell membrane
2. What kind of molecules CAN go through the
phospholipid bilayer?
3. What kinds of molecules CANNOT go through the
phospholipid bilayer?
4. What is facilitated diffusion?
5. Can any molecule go through any protein channel?
6. When will the molecules stop noticeably moving?

17. Describe a person
who is passive.
Describe a person
who is active.

18. Passive Transport:
> Materials move down
the concentration gradient
from high to low solution
concentrations
> Equilibrium is reached
(concentrations are equal
all around)
> No energy (ATP) is
needed by the cell to
move the materials

19. Active Transport:
1. Materials move up the
concentration gradient,
from low to high solution
concentrations
2. Concentrations
become unbalanced on
either side of the
membrane
3. Energy (ATP) is
needed by the cell to
move the materials

20. Diffusion
Facilitated
Diffusion
Osmosis
1. Passive
Transport
Protein
Pumps
Endocytosis
Exocytosis
2. Active
Transport
There are two ways that materials can
move in/out of the cell

21. 1. Protein Pumps use energy (ATP,
electrons) to increase the concentration on
one side of the membrane

22. The Sodium-Potassium (Na+/K+) Pump
uses ATP to move Na+ out and K+ into
nerve, muscle and many other cells.

23. Protein pumps are found cooperating with
protein channels in
photosynthesis and cell respiration

24. 2. Endocytosis: Materials enter the cell without
crossing the membrane—the membrane folds
around the particles and forms a new vacuole
inside the cell

25. Amoeba and white blood cells engulf large
food particles through phagocytosis (a type
of endocytosis).
http://www.youtube.com/watch?v=pvOz4V
699gk (mute: annoying soundtrack)

26. Paramecium Feeding
http://www.youtube.com/watch?v=sn3MTYNe8mM

27. 3. Exocytosis: Vesicles fuse to the cell
membrane to release their contents (cell products
or waste)

28. Phospholipids from vesicle membranes
integrate into the plasma membrane

29. Exocytosis in Paramecium
http://www.youtube.com/watch?v=U9pvm_4-bHg

30. 1. What materials can diffuse through the
lipid bilayer without the aid of a protein?
2. What is the difference between facilitated
diffusion and the use of a protein pump?
3. What are the major differences between
Passive Transport and Active Transport?
4. Explain why an animal cell bursts when
placed in a hypotonic solution.