Notes on Passive Transport (Diffusion, Osmosis, etc.)
Relate concentration gradient, diffusion and equilibrium
Predict the direction of water movement into and out of cell
Describe the importance of ion channels in passive transport
Identify the role of carrier proteins in facilitated diffusion
5 types of Passive Transport
1. Diffusion
2. Osmosis
3. Diffusion Through Ion Channel
4. Electrical Charge & Ion Transport
5. Facilitated Diffusion
Passive Transport: movement across the cell membrane that does not
require energy from the cell (NO ENERGY)
O
O
O
O
O
O
Equilibrium: condition in which the concentration of substance is equal
Concentration Gradient: A difference in the concentration of substance
across a space
(Figure 1 page 75)
 You can also add food coloring to water and see how long it takes to
get fully distributed
Movement of Substances
Go from high
concentration
to a lower
concentration
1. Diffusion: high to low concentration cause by random motion until
they are at equilibrium
(Simplest form)
 Many ion dissolve in cytoplasm and in fluid outside the cell
 Allows ions to enter or leave cell by diffusion
 Substance must be able to pass through the cell membrane
O
O
O
Notes on Passive Transport (Diffusion, Osmosis, etc.)

2. Osmosis:
 H20 molecules can diffuse through channels in the cell membrane
 Diffusion of H20 through a selectively permeable membrane
 Use the concentration gradient (high to low)
Hypertonic, Hypotonic and Isotonic
1. Hypertonic Solution
a. H20 moves out
b. Cell will shrink
Notes on Passive Transport (Diffusion, Osmosis, etc.)
2. Hypotonic Solution
a. H20 moves in
b. Cell swells
c.
3. Isotonic Solution
a. No net movement of H20
3. Diffusion through Ion Channel
Ions: Na+ (Sodium)
Ca+2 (Calcium)
K+ (Potassium)
Cl- (chloride)
 Ion are essential for the ability of nerve cells to send electrical signals
throughout boy
 EX. Heart would not beat if it was not for ion channels
o Not diffuse through nonpolar interior
 Ion Channel: transport protein with a polar pore through which ions
pass
o (Never touching nonpolar membrane)
Notes on Passive Transport (Diffusion, Osmosis, etc.)
o
o Opening by stretching cell membrane, change in charge and
binding of specific molecules to the ion channels
o Uses NO ENERGY
o Goes from high concentration of ions to a low concentration of
ions
4. Electrical Charge & Ion Transport
 Inside cell is (-) charge
 (+)  (-) & (-)  (+)
Opposites attract
 (+)  (+) & (-)  (-)
This does not happen because similar ions
do not attract
 More negatively charged ions will diffuse out of cell
o The cell is always more negatively charged
5. Facilitated Diffusion
 Transport protein that can bind to a specific substance on one side of
cell membrane and carry the substance across the cell membrane, &
release it on the other side
 Carrier Protein: used to transport specific substances-such as amino
acids & sugars – down their concentration gradient
STEPS IN FACILIATATED DIFFUSION
1. The carrier protein binds a specific molecule on one side of the cell
membrane
2. A change in the shape of the carrier protein exposes the molecule to
the other side of the cell membrane
3.