CELLULAR TRANSPORT
OSMOSIS AND DIFFUSION!
Ch. 7
See how it flows!
Transport
Every
living cell exists in a liquid
environment.
The cell membrane regulates movement of
dissolved molecules (e.g. oxygen, glucose
& carbon dioxide) from the liquid on one
side of the membrane to the liquid on the
other side.
The plasma membrane is responsible for
maintaining homeostasis in the cell!
Selective Permeability



Permeable = allows things to pass through
Selectively Permeable = allows certain things
only to pass through
Impermeable = allows nothing to pass
through
Structure of the Cell Membrane
Carbohydrate Chain
Proteins
Phospholipid
bilayer
So how do materials enter and exit the cell??
Passive Transport:
 Movement that does not require
energy
 Particles move from areas of HIGH
concentration to LOW concentration
 Particles move WITH the concentration
gradient
Concentration Gradient

An uneven balance of molecules in
a given area
3 Types of Passive Transport
Simple Diffusion
2. Facilitated Diffusion
3. Osmosis
1.
1) Simple Diffusion

The random movement of molecules
from an area of high concentration to
an area of lower concentration.
Low
conc.
High
conc.
Simple Diffusion
When everything is the same concentration it
is said to be at dynamic equilibrium.
 Are things still moving?

 Yes!
All the same concentration
Simple Diffusion
2) Facilitated Diffusion

Sometimes this passive transport of
molecules across the membrane requires
the aid of transport proteins.
3) Osmosis
The diffusion of water across a
semipermeable membrane.
 Water always tries to reach an
equal concentration on both sides of
the membrane.
 Solute = you add
 Solvent = added to

Osmosis
Concentrated
sugar solution
(Water less
concentrated)
Dilute sugar
solution
(Water more
concentrated)
Sugar
molecules
Selectively permeable
membrane
Movement of
water
Osmosis: Scenario #1
A cell is placed in pure
water.
 Which has a higher
concentration of water:
inside or outside the
cell?
 Predict what is going to
happen.

Osmosis: Scenario #1
Hypotonic Solution  Hypo- means below
 Lower concentration of
solutes outside the cell
than inside.
 Water will flow into the
cell to maintain
homeostasis.
Osmosis: Scenario #2
A cell is placed in saline
solution.
 Which has a higher
concentration of solutes:
inside or outside the
cell?
 Predict what is going to
happen.

Osmosis: Scenario #2
Isotonic Solution  Iso- means same
 Equal concentrations of
solutes inside as outside.
 Water will flow into
and out of the cell at
equal rates to maintain
homeostasis.
Osmosis: Scenario #3

Cell is placed in a
concentrated salt solution
(seawater)
Which has a higher
concentration of solutes,
inside or outside the cell?
 Predict what is going to
happen.

Osmosis: Scenario #3
Hypertonic solution  Hyper- means above
 Higher concentration of
solutes outside the cell than
inside.
 Water will flow out of the
cell to maintain
homeostasis.
Osmosis: Scenario #3

The cell will shrink
since all of the water
is leaving the cell.
OSMOSIS
A Review of Osmosis
Note: These are animal red blood cells.
The size of the arrows indicates the magnitude and
direction with which water moves.
Cellular Transport
Hungry?
ENDOCYTOSIS: cells surrounds and takes in
material from environment by engulfing the
material!
 EXOCYTOSIS: cells expel materials from cell,
such as waste or indigestible particles.
 Both endo and exocytosis are moving large
masses of material and require energy
(ACTIVE TRANSPORT!)

Endocytosis
Exocytosis