Osmosis and Diffusion!
IMPORTANT DEFINITIONS

DIFFUSION: movement of particles from
higher concentration to lower
concentration
DIFFUSION

OSMOSIS: diffusion of water across a
selectively permeable membrane
In a cell, water always tries to reach an equal
concentration on both sides of the
membrane!
OSMOSIS
Vocabulary Terms to Know

Concentration = density of particles
Permeable = allows things to pass through
 Selectively Permeable = allows certain
things only to pass through
 Impermeable = allows nothing to pass
through
 Solute = you add
 Solvent = added to

During osmosis, only water
diffuses across the selectively
permeable membrane.
OSMOSIS
Gotta love the Greeks!
ISOS=equal
HYPO=under
HYPER=over
Remember your roots!
Hypotonic Solution



A cell is placed in pure
water
There is a lower
concentration of
solutes (dissolved
substances )outside the
cell than inside the cell.
Water will flow into the
cell.
Isotonic Solution



Equal concentrations of
solutes inside and
outside the cell.
Water will flow into and
out of the cell at equal
rates (dynamic
equilibrium)
EX: Immunizations are
isotonic solutions so
they do not damage the
cells by gain or loss of
water.
Hypertonic Solution



A cell is placed in a
concentrated salt
solution (seawater)
There is a higher
concentration of
solutes outside the cell
than inside the cell.
Water will flow out of
the cell
Note: These are animal red blood cells.
The size of the arrows indicates the magnitude and
direction with which water moves.
What about the big boys?



ENDOCYTOSIS: cells surrounds and takes in
material from environment by engulfing the
material! YUMMY!
EXOCYTOSIS: cells expel materials from cell, such as
waste or indigestible particles. GROSS!
Both endo and exocytosis are moving large masses
of material and require energy (ACTIVE
TRANSPORT!)
Endocytosis
Exocytosis
ISOTONIC SOLUTIONS!




Concentration of dissolved substances in solution is
the same as concentration of dissolved substances
inside the cell.
Water inside cell is equal to water in solution.
Cells in isotonic solution do not experience osmosis
and retain their normal shape.
EX: Immunizations are isotonic solutions so they do
not damage the cells by gain or loss of water.
HYPOTONIC SOLUTIONS!





Concentration of dissolved substances is lower in
solution outside the cell than concentration inside
the cell.
There is more water outside the cell than inside.
Cells in hypotonic solutions experience osmosis in
which water moves through membrane into cell.
EX: In animal cells, the pressure inside cell
increases causing the cells to swell and sometimes
burst!
EX: In plant cells, the rigid cell wall prevents
bursting, but the cells become more firm.
CUCUMBERS IN THE MIST!
HYPERTONIC SOLUTIONS!





Concentration of dissolved substances outside cell
is higher than concentration inside cell.
There is more water inside cell than outside.
Cells in hypertonic solutions experience osmosis in
which water moves through membrane to
outside of cell.
Ex: In plant cells, membrane and cytoplasm
shrink away from cell wall and plant wilts.
EX: In animal cells, the pressure decreases and the
cells shrivel.
Don’t be so SALTY!
Passive Transport: Mosey on
through…
Passive transport is what it sounds like!
 Molecules pass through the membrane by
diffusion requiring no extra energy.
 The molecules just mosey on through the
membrane.
 Ex: Some of the molecules that move by
passive transport are: water and lipids

Passive Transport
Facilitated Diffusion: Help them
out a bit!
Remember those transport proteins in the
phospholipid bilayer? Here’s where they fit in!
 Facilitated diffusion: passive transport across
membrane with help of transport proteins.
 Ex: Facilitated diffusion is used to move
sugars and amino acids across membranes.
Facilitated Transport
Active Transport: ENERGY
REQUIRED!
Active transport is the movement of
materials through a membrane across a
concentration gradient.
 This requires energy to counteract the
movement of diffusion from high to low
concentrations!

How does it work?
1)
2)
3)
Transport protein called “carrier protein” binds
with particle that is going to be transported.
Because of its specific shape, the carrier protein
can bind to the particle and with some energy,
it can move through the membrane.
Once the particle is released, the protein
returns to its original shape.
Active transport allows a particle movement into
or out of a cell against a concentration
gradient.
How carrier proteins work!
Active Transport
Active Transport
Cellular Transport