1. Diffusion Through a Membrane

2. Diffusion Through A Membrane
Semi-permeable – some molecules are able to pass through while others can't
WHY?
Size and/or Shape 2

3. Diffusion Through A Membrane
Glucose – small sugar molecule (simple sugar)
Starch – several small sugar molecules bonded together
Which is larger? 3

4. 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 4

5. Diffusion Through A Membrane
Diffusion – movement of molecules from high concentration to low concentration
– no energy needed (this is called passive transport) 5

6. 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 6

7. Diffusion Through A Membrane
The initial set up
The “Cell” filled with glucose and starch solutions
Water & Iodine in the beaker cover the “cell”

8. 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

9. Diffusion Through A Membrane – Pg 3
Chemical Test Results
Amber-Colored Starch Indicator Solution (Iodine) Changes in presence of starch
*If it changes from amber to dark purple/black, starch is present! (The result is positive).

10. Diffusion Through A Membrane – Pg 3
*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).
Blue-colored Glucose Indicator Solution (Benedict's Solution)

11. Diffusion Through A Membrane – Pg 3 Table Two – Chemical Test Results
Indicator Solution Used
Distilled Water
Starch
Glucose
Blue Colored BENEDICTS
*HEATED!
Amber Colored IODINE

12. Diffusion Through A Membrane – pg 4
Record any color changes observed in the “cell” and in the beaker
Initial State

13. Diffusion Through A Membrane
Final State:
What Color is the Cell Now?
What does that mean?

14. Diffusion Through A Membrane – pg 4
Record any color changes observed in the “cell” and in the beaker
Final State

15. Diffusion Through A Membrane –Pg 4
Initial State
Final State

16. Diffusion Through a Membrane16

17. Initial and Final State
I = Iodine
S = Starch
G = Glucose I I I I I I I I I S G S S S G G I I I I
Use the letters I, S, and G to represent the substances used.

18. Diffusion Through A Membrane
glucose molecule
part of a starch
molecule 18

19. Diffusion Through a Membrane
Red Onion Cells
Normal/Healthy Environment

20. Cell membrane is pressed against the inside of the cell wall
Diffusion Through a Membrane
cytoplasm
red onion cells
in tap water
cell membrane
cell wall
Cell membrane is pressed against the inside of the cell wall 20

21. Diffusion Through a Membrane
bathing the cells in
10% NaCl
(salt water)
NaCl 21

22. Cell membrane and cytoplasm have shrunk because water diffused out
Diffusion Through a Membrane
cytoplasm
red onion cells in
salt water
cell membrane
cell wall
Cell membrane and cytoplasm have shrunk because water diffused out 22

23. Which is in distilled (pure) water and
Diffusion Through A Membrane
Which is in distilled (pure) water and
which is in salt water? 23

24. 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 24

25. 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.

26. 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.

27. 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….

28. 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.

29. 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

30. 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