The Cell Membrane
What is a membrane?

A membrane is a
device that selectively
permits the
separation of one or
more materials from a
liquid or gas.
?
Passive Transport
 The
transport
of substances
through the
cell
membrane
without using
energy.
 Now
there are two different ways to
transport material through the cell
membrane WITHOUT using energy:
Diffusion and Osmosis
Diffusion
 The
process
of moving
from areas of
high
concentration
to areas of
low
concentration
Diffusion Demonstration Model
 Molecules
are always in motion
 In a closed system the molecules evenly
try to distribute
 Which results in a the initial movement of
molecules from high to low concentrations
 Once an equilibrium is reached there is no
net movement of molecule.
 What
is separating the two different types
of beads?
 How do the two volumes compare in this
model?
 Which side of the model has a higher
concentration of beads?
 How is diffusion going to take place?
 What happens with continued shaking?
 Is equilibrium reached? (Has homeostasis
been reached?)
Add: Homeostasis
is
the maintenance of a
stable internal
environment.
Dialysis
 It’s
a process that separates solvents from
blood. Such as removing glucose or fats
with out removing the important molecules
that our blood needs.
 The tubing used in semi-permeable.
Meaning some material can pass through
and other cannot.
Osmosis
Osmosis
 The
diffusion of
water from areas
of high
concentration to
areas of low
concentration
through a semipermeable
membrane.
 Water
moves from a high concentration of
water (less salt or sugar dissolved in it) to
a low concentration of water (more salt or
sugar dissolved in it). This means that
water would cross a selectively permeable
membrane from a dilute solution (less
dissolved in it) to a concentrated solution
(more dissolved in it).
 Water
can cross the cell membrane
through the lipid bi-layer and with
special proteins. If enough water enters
the cell by osmosis, the cell can swell
enough to burst open and die. This is
demonstrated in the picture.

In this picture a red blood
cell is put in a glass of
distilled water (all water
with no salt or sugar in
it). Because there is a
higher concentration of
water outside the cell,
water enters the cell by
OSMOSIS. In this case
too much water enters
and the cell swells to the
point of bursting open. In
the end pieces of cell
membrane are left in the
water.
Osmosis Cont.
The
concentration (amount) of
all substances affects the
movement of materials in and
out of the cell.
Hypotonic
Solute concentration: contains a low
concentration of solute
Water concentration: contains a high
concentration of water
Water movement: water diffuses into the
cell
Effect on the cell: causing the cell to swell
and possible explode
Cells in hypotonic solution
Draw a picture
Isotonic
 Solute
concentration: is equal to the
water concentration
 Water concentration: is equal to the
solute concentration
 Water movement: equal diffusion (water
diffuses into and out of the cell at equal
rate)
 Effect on cell: none
Normal cells in isotonic solution
Draw a picture of an isotonic
solution next to the definition
Hypertonic
Solute concentration: contains a high
concentration of solute
Water concentration: contains a low
concentration of water
Water movement: water diffuses out of the
cell
Effect on the cell: causing the cell to shrivel
Cells in hypertonic solution
Draw a picture next to the definition
Quiz yourself
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2
3
Active transport
Active transport

The transport of
molecules from areas
of high to low
concentration with the
use of energy.
 The cell energy is the
ATP made in the
mitochondria.
Bulk movement of substances
across the membrane
Endocytosis:
 Phagocytosis
 Pinocytosis
Exocytosis
Endocytosis

A process by which a cell surrounds and takes in
materials from its environment by engulfing
them.
Phagocytosis
 Process
in which phagocytes engulf and
digest microorganisms and cellular debris

"phagocyte" or eating cell
(phago = "eating", cyte = "cell").
 An
important defense against infection
Pinocytosis

process by which
certain cells can
engulf and
incorporate droplets
of fluid
Exocytosis
when
transport
is out of the
cell.