1. The plasma membrane is a two-layered lipid bilayer structure made of phospholipid molecules with embedded protein molecules. 2. The fluid mosaic model describes the plasma membrane as a fluid structure where molecules can move freely. Different proteins and lipids give each membrane its specific permeability properties. 3. Transport across the membrane includes passive diffusion, facilitated diffusion, osmosis, and active transport. Osmosis involves the diffusion of water across the membrane from high to low concentration areas.

1. 1. Structure of Plasma membrane
* Two-layered structure:
lipid bilayer
*Made of lipid molecules
with protein molecules in
the lipid layer.
**PROTEINS aid in the
movement of materials
through the membrane

2. extracellular fluid
(watery environment)
phospholipid hydrophilic
heads
hydrophobic
tails
bilayer
hydrophilic
heads
cytoplasm
(watery environment)

3. Polar Head
Non-Polar Tails
tails
(hydrophobic)
head
(hydrophilic)

4. * Bilayer can be considered a liquid
 FLUID MOSAIC MODEL:
plasma membrane : made up of molecules that are
free to flow among one another.
 Kinds and arrangements of proteins + lipids vary
from one membrane to another and give each type of
membrane specific permeability properties.

5. Polar heads Fluid Mosaic Model
love water & of the cell
dissolve. membrane
Non-polar Membrane
movement
tails hide animation
from water.
Carbohydrate cell
markers
Proteins

6. Structure of the Cell Membrane
Outside of cell
Carbohydrate
Proteins chains
Lipid
Bilayer
Transport
Protein Phospholipids
Animations
of membrane Inside of cell
structure (cytoplasm)
Go to
Section:

7. 1. Maintaining a BALANCE in a
CELL
Cells Maintain HOMEOSTASIS : internal balance
Selective permeability : allows
some materials to pass through
membrane while rejecting
others.

8. Diffusion
 Movement of molecules
high concentration to
lower concentration
 Example: skunk,
perfume, night after a
dinner at Taco Bell!

9. 2 Dye molecules
diffuse into the 3 Both dye molecules
1 A drop of dye is water; water and water molecules
placed in water. molecules diffuse are evenly dispersed.
into the dye.
drop of dye
pure water
Diffusion animation

10. Osmosis
 The diffusion of
Water from areas
of high
concentration to
areas of low
concentration
Animation: How Osmosis Works

11. Transport across membranes
Passive transport of water by Osmosis
• a. Isotonic
• b. Hypertonic
• c. Hypotonic

12. Isotonic Solution:
 Solution concentration of water (solvent) outside
of the cell is the same as concentration inside
the cell (Animal cell normal / plant flaccid)

13. Hypotonic Solution: concentration of water (solvent)
outside the cell is higher than concentration inside the cell.
Water rushes into the cell!
  Turgor pressure: Pressure that builds in a plant
cell as a result of osmosis. Makes a plant cell firm.
(Turgid) Plant cells are healthiest in a hypotonic
environment.
  Lysed: pressure builds in animal cell (burst)

14. Hypertonic Solution: concentration of water (solvent)
outside cell is lower than concentration inside the cell.
Water rushes out of the cell!
 Plasmolysis: loss of water from within a plant cell,
causing cytoplasm to shrink, pulling inner plasma membrane
away from cell wall. (wilting of plants)
 Crenation: (crenates: shrinks) animal cell loses water
and it shrinks (collapses)

16. What type of solution are these cells in?
A B C
Hypertonic Isotonic Hypotonic

17. 10 micrometers
(a) isotonic solution (b) hypertonic solution (c) hypotonic solution
equal movement of water net water movement net water movement
into and out of cells out of cells into cells

18. 5. PASSIVE TRANSPORT: No energy
required for this to happen
 Passive transport : movement of substances
across plasma membranes without additional energy
 Facilitated diffusion: diffusion of materials across
a plasma membrane by transport (channel) proteins.

19. 6. ACTIVE TRANSPORT:
Requires energy in the form of ATP
 Active Transport : gradient from low to high.
Energy is required.
 Proteins throughout the membrane are “carriers”
used for this purpose.

20. Sodium-potassium pump
Na  out K  in
ACTIVE TRANSPORT = ATP
 Na+ ions: moved out of cell
 K+ ions: moved by the
same carrier into the cell

(This process is important in nerve and muscle function.)

21. 7. TRANSPORT of LARGE
PARTICLES
• Endocytosis (Endo = In): cell surrounds and takes in
material from environment. Material does not pass through the
membrane; instead, it is engulfed and closed by a portion of
membrane and cytoplasm.
 Pinocytosis: water
 Phagocytosis: food/ minerals/
large particles
• Exocytosis (Exo = Out):
transport of materials out of cell
across cell membrane.

22. Exocytosis

23. (a)
Animated Review of Phagocytosis,
Pinocytosis and Receptor Mediated
pinocytosis
(extracellular fluid) Endocytosis.
Click on Active Transport, watch the
brief overview of Active Transport and
1 then click on Endocytosis in the bar below
the animation
3
2
vesicle containing
extracellular
(cytoplasm) fluid
cell (b)
phagocytosis
food particle
pseudopod
1 2 3
particle
enclosed in vesicle