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