Download Living Environment - Wappingers Central School District

Diffusion
Through a
Membrane
Diffusion Through A Membrane
indicator – chemically indicates if a substance
is present by changing color
Iodine = starch indicator solution
Benedict’s solution = glucose indicator
solution – must be heated
Diffusion Through A Membrane
Diffusion – movement of molecules from an
area of high concentration to a region of low
concentration – no energy needed (this is
called passive transport)
Diffusion Through A Membrane
 we
will use dialysis tubing to make a model of a cell.
 the tubing represents a semi-permeable cell membrane
 the dialysis tube is filled with a glucose solution and a starch
solution, sealed and rinsed with water
 it will be placed in a beaker with water and iodine (an indicator)
and allowed to sit
Diffusion Through A Membrane
The initial
set up
The “Cell” filled
with glucose and
starch solutions
Water & Iodine
in the beaker
cover the “cell”
Diffusion Through A Membrane – Pg 2

Question #9: Predict what you think will
diffuse.


Remember: There’s starch and glucose inside the
“cell” and iodine outside the cell.
Write which way you think the substances will
move (into or out of the cell).


NO WORRIES! You will not be marked wrong if
your prediction (hypothesis) is incorrect!!! (So
write what you think!)
Make sure you list ALL three substances:

STARCH, GLUCOSE and IODINE
Diffusion Through A Membrane – Pg 3
•Chemical Test Results
Amber-Colored Starch
Indicator Solution
(Iodine):
*If it changes from
amber to dark
purple/black, starch is
present (the result is
positive for glucose).
Diffusion Through A Membrane – Pg 3

Blue-colored Glucose
Indicator Solution
(Benedict's Solution)
*Remember that you
must HEAT the test
tubes with the
Benedict’s Solution for
this INDICATOR to
change color!
*If it changes to
orange/red when
heated, glucose is
present (the result is
positive for glucose).
Diffusion Through A Membrane – Pg 3
Table Two – Chemical Test Results
Indicator
Solution
Used
Blue Colored
BENEDICTS
*HEATED!
Amber
Colored
IODINE
Distilled
Water
Starch
Glucose
Diffusion Through A Membrane – pg 4

Record any color changes observed in the
“cell” and in the beaker
Initial State
Diffusion Through A Membrane
Final State:
What Color
is the Cell
Now?
What
does that
mean?
Diffusion Through A Membrane – pg 4

Record any color changes observed in the
“cell” and in the beaker
Final State
Diffusion Through A Membrane – pg 4
Initial State
Final State
Diffusion Through a Membrane
Initial and Final State
I I I
I
S G
S S
G G
I
I = Iodine
S = Starch
G = Glucose
I
I
I
Use the letters I, S, and G to represent the substances used.
Diffusion Through A Membrane
glucose molecule
part of a starch
molecule
Diffusion Through a Membrane

Red Onion Cells

Normal/Healthy Environment
Diffusion Through a Membrane
cytoplasm
cell membrane
cell wall
red onion cells
in tap water
Cell membrane is pressed against the
inside of the cell wall
Diffusion Through a Membrane
bathing the
cells in
10% NaCl
(salt water)
NaCl
Diffusion Through a Membrane
cytoplasm
cell membrane
red onion cells in
salt water
cell wall
Cell membrane and cytoplasm have
shrunk because water diffused out
Diffusion Through A Membrane
Which is in distilled (pure) water and
which is in salt water?
Diffusion Through A Membrane
Applications:
 salt on roads to melt snow
 intravenous saline solutions
 salty foods make you thirsty
 salt on slugs to kill them
 salty foods do not spoil as easily
 gargling with salt water
Isotonic

"ISO" means the same

If the concentration of
solute (salt) is equal
on both sides, the
water will move back
in forth but it won't
have any result on the
overall amount of
water on either side.
When Placed in Hypertonic Solution

Plant cells, the central vacuole loses water
and the cells shrink, causing wilting.

Animal cells, the cells also shrink, called
crenation.

In both cases, the cell may die.
Hypertonic


The word "HYPER"
means more…
In this case there are
more solute (salt)
molecules outside the
cell, which causes the
water to leave the cell
 Moving from high water
concentration inside the
cell to a lower
concentration outside
the cell
 Solutes can be salt or
sugar or nutrients….
When Placed in Hypertonic Solution

Plant cells, the central vacuole loses water
and the cells shrink, causing wilting.

Animal cells, the cells also shrink, called
crenation.

In both cases, the cell may die.
Hypotonic



"HYPO" means less
There are less solute (salt)
molecules outside the cell,
which causes the water to
enter the cell
Remember: if there are
less solute particles, then
there are more water
molecules.

Water moves from high
concentration outside the
cell to low concentration
inside the cell
When Placed in a Hypotonic Solution

In plant cells, the central vacuoles (large
storage areas) will fill and the plant becomes
stiff and rigid (called turgor), the cell wall
keeps the plant cell from bursting

Animal cells are in danger of bursting
because they don’t have a rigid cell wall


When the cell bursts it is called hemolysis
When it bursts, it dies