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Diffusion Through a Membrane
Diffusion Through A Membraneindicator – chemically indicates if a substance
is present by changing color
Iodine = starch indicator solutionBenedict’s solution = glucose indicator solution – must be heated
Diffusion Through A MembraneDiffusion – 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 MembraneThe initial
set up
The “Cell” filled with glucose and starch solutions
Water & Iodine in the beaker cover the “cell”
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 2
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).
Indicator Solution Used
Distilled Water
Starch Glucose
Blue Colored BENEDICTS*HEATED!
Amber Colored IODINE
Diffusion Through A Membrane – Pg 3Table Two – Chemical Test Results
Record any color changes observed in the “cell” and in the beaker
Diffusion Through A Membrane – pg 4
Initial State
Diffusion Through A MembraneFinal State:
What Color is the Cell Now?
What does that mean?
Record any color changes observed in the “cell” and in the beaker
Diffusion Through A Membrane – pg 4
Final State
Diffusion Through A Membrane – pg 4
Initial State Final State
Diffusion Through a Membrane
Initial and Final State
Use the letters I, S, and G to represent the substances used.
I = IodineS = StarchG = Glucose
S
I I I I I I I I
I I
SSS
I
G G G
I I
Diffusion Through A Membrane
glucose molecule
part of a starchmolecule
Red Onion Cells Normal/Healthy Environment
Diffusion Through a Membrane
Diffusion Through a Membrane
cell wall
cytoplasm
red onion cellsin tap water
cell membrane
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
red onion cells insalt water
cytoplasm
cell wallcell membrane
Cell membrane and cytoplasm have shrunk because water diffused out
Diffusion Through A Membrane
Which is in distilled (pure) water andwhich is in salt water?
Diffusion Through A MembraneApplications: 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