 Diffusion is the movement of any molecule from an area of higher
concentration to one of a lower concentration (concentration gradient)
through a solid, liquid or gas.
 A drop of food coloring put in a glass of water will diffuse at a constant rate
until the concentration of colorant is equal in all the water.
 The perfume of a flower, which are none other than chemical molecules,
move through the air by diffusion at a constant rate until the whole room
smells like the flower.
 Mercury can diffuse through your skin and cause toxic effects in your
nervous system.
 Osmosis is a specialized type of diffusion. It is the diffusion of water
molecules across a selectively permeable membrane.
 If you leave the celery out of the fridge for a few hours, it becomes wilted. If
you submerge it in water for a few hours it regains its crisp consistency.
That is due to water moving into the cell by osmosis.
2
 When comparing the concentration of solutes in
different solutions, the terms hypotonic, hypertonic
and isotonic are used.
 A solution consists of solute(s) + solvent.
 Lemonade
lemon juice + sugar (solutes)
water (solvent)
3

Hypotonic
Isotonic
Hypertonic
(lower than)
(equal to)
(higher than)
Hypotonic
Water concentration
outside is higher than that
inside the cell, the water
moves inside the cell.
Isotonic
Water concentration
is equal in and out of
cell. There is no net
movement.
Hypertonic
Water concentration is
lower outside the cell,
the water moves outside
the cell.
4
 Higher temperatures tend to increase the rate of
diffusion.
 2 agar plates are prepared.
 Two holes are made in each of the agar plates.
 One plate will be kept at room temperature (25˚C)
 One plate will be put in the incubator at 37˚C
Potassium
Permanganate
(294 Daltons)
Janus
Green
(511 Daltons)
In both plates, each well is filled with a
solution and both plates are kept at it’s
required temperature for 30 minutes
5
Potassium
Permanganate
Janus
green
Results: n0 diffusion on both
Time: 0 minutes
Potassium
permanganate
Janus
green
21 mm
15 mm
Time: 30 minutes
The diameter of the diffusion in each one of the dyes
was measured by the distance from edge to edge.
6
Potassium
permanganate
Janus
green
0 diffusion on both
0 minutes
Potassium
permanganate
17 mm
Janus
green
14 mm
30 minutes
Conclusions:
1. The lower the temperature, the slower the rate of diffusion.
2. The higher the molecular weight, the lower the rate of diffusion.
7
 Dialysis tubing is a semi-permeable material that can be used to
simulate the movement of substances through cell membranes (cell
membranes are selectively permeable).
 The pores on the dialysis tubing are large enough to allow water
molecules, other small molecules and ions to move through
unrestricted. Larger molecules, such as sucrose, cannot cross because
of their size.
Roll of dialysis tubing
8
 A 12 cm piece of tubing was cut and filled with a solution. The ends
were tied with string. The resulting bag represents a cell. The bag is
then placed in a beaker and the contents of beaker represent the
environment that surrounds cells.
Bag of solution
Bag in beaker with solution
9
 3 bags were prepared according to the information on the table below.
 3 beakers were prepared according to the information given below.
 The bags were placed in the beakers and left for 40 minutes.
1
N°
Bag contents
Beaker contents
1
10 ml 10% sucrose
200 ml dH2O
2
10 ml dH2O
200 ml 10% sucrose
3
10 ml 10% sucrose
200 ml 10% sucrose
2
3
10
N°
Bag contents
Beaker contents
Weight change
1
10 ml 10% sucrose
200 ml dH2O
+ 5.65 grams
2
10 ml dH2O
200 ml 10% sucrose
- 4.89 grams
3
10 ml 10% sucrose
200 ml 10% sucrose
no change
Conclusions: Water will move from high concentration of water to areas of
lower concentration.
11
 The solution contains a mixture of starch, protein, sodium chloride,
and sodium sulfate in an aqueous solution. Starch and protein are both
macromolecules.
 Sodium chloride (NaCl), will dissociate in an aqueous solution to
produce sodium ion (Na+) and chloride ion (Cl -).
 Sodium sulfate (Na2SO4) will dissociate in an aqueous solution to
produce sodium ion (Na+) and sulfate ion (SO4⁻²).
 Dialysis tubing is a material that will be used to simulate differentially
permeability of membranes. Only molecules and ions smaller than the
pores of the tubing will be allowed to cross.
12
The flask contains starch, protein, sodium chloride, and
sodium sulfate in an aqueous solution.
A bag is prepared containing this cocktail.
The bag is then placed in a beaker of distilled
water for 40 minutes.
13
 Tests for the presence of:
Starch with iodine
+
-
Protein with Biuret
+
-
Chloride ions with silver nitrate (AgNO3)
Sulfate ions with barium chloride (BaCl2)
+
-
NOTE: It is difficult to see the white precipitate in this last
case. You have something resembling chalk dust collecting at
the bottom of the test tube. You may need to shake the tube.
+
14
After 40 minutes these were the results of the experiment:
Tube 1: test for starch
Tube 2: test for protein
Tube 3: test for chloride ions
Tube 4: test for sulfate ions
1
2
3
4
Conclusions: Only sulfate and
chloride ions are small enough
to go through the pores of the
membrane.
-
-
+
+
15
 Water flows across membranes unrestricted. It flows from a region of
lower solute concentration to a region of higher solute concentration
until equilibrium is established.
 Plant cells have cell walls which support the cell and keep it from
osmotic shock. Animal cells do not have cell walls and may rupture
unless they have a mechanism for stabilizing the osmotic differences.
16
 These test tubes contain 4 drops of sheep blood in a saline solution.
 Tube A contains 10% NaCl solution (hypertonic solution).
 Tube B contains 0.9% NaCl solution (tonicity similar to that of blood
plasma, isotonic solution).
 Tube C contains 0.45% NaCl solution (hypotonic solution).
A
B
C
hyper tonic isotonic hypotonic
17
 Notice the crenation
shown by the
membrane collapsing
due to loss of water.
100x
18
 Notice the round and
smooth shape the red
blood cells show in
this picture.
40x
19
 Very few or no cells are
40x
seen in this condition as
water flows in causing the
bursting of the cells.
20
 Two beakers have been prepared and Elodea (an aquarium plant) has
been placed in each of the beakers.
 Beaker A contains 0% NaCl solution (hypotonic solution).
 Beaker B contains 20% NaCl solution (hypertonic solution).
A
B
21
chloroplasts
vacuole
Normal turgid cell in a
hypotonic solution.
Water moves into the
cells, chloroplasts are
pushed to the sides due
to the enlarged central
vacuole where water is
stored.
A
22
 Plasmolyzed cells are present
due to the hypertonic
condition that makes the
water move outside the cell,
causing the membrane to
collapse.
 It is characteristic to see the
chloroplasts clumped in the
center of the cell, with the
membrane surrounding them.
Cell membrane
End
B
Clumped chloroplasts
23