Diffusion

Activity 1Diffusion Through a Semi-Solid Agar Gel

Supplies:(1) Agar PlateMillimeter-rulerWax marking pencil(2) Tweezers(1) Jar of Methylene Blue(1) Jar of Potassium Permanganate

Experiment:1. Make sure your tweezers are washed prior to using.2. Using the wax marking pencil draw a line on the bottom of the petri dish

to divide the dish in half.3. Using the flat end of your tweezers create a well in the center of each side

of the agar plate. Don't dig so deep into the agar that you reach the plastic.

4. Use your tweezers to take a pinch of methylene blue from the jar and place it in one well in the agar plate.a. Make sure you hold your hand underneath the tweezers prior to

carrying the methylene blue to the agar plate or you’ll have freckles all over the plate.

5. Repeat step 4 using the potassium permanganate6. Place the lid back over the agar plate and let sit for approximately 1 hour7. At the end of the hour measure to determine which dye diffused through

the agar the farthest.

Record your results:_________________ moved through the gel the fastest

Why did this chemical move through the gel the fastest? ________________________________________________________________________________________________

Activity 2Diffusion Through a Liquid

Experiment:

1. Obtain two graduated cylinders and fill with cold water2. Let the graduated cylinders sit undisturbed at your table for a couple of

minutes so the water can settle 3. Take a pinch of methylene blue and add to the first graduated cylinder4. Take a pinch of potassium permanganate and add to the second

graduated cylinder5. Watch the dye move through the water over the next several minutes.6. Record which dye moves through the water fastest.

a. What you’re looking for is to see which graduated cylinder no longer has no clear water.

b. You are not looking for an even blue or even pink shade throughout the graduated cylinder.

Record your results:___________________ moved through water the fastest

Why did this chemical move through the water the fastest? ________________________________________________________________________________________________

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Activity 3Diffusions Through a Semi-permeable Membrane

Supplies:(3) Dialysis membranes(3) Beakers(6) Clips(2) Test tubes of NaCl (Green)(2) Test tubes of Glucose (Red)(2) Test tubes of Starch (White)(2) Test tubes of Benedict’s Solution (Blue)(4) Empty Test tubes

Experiment:

1. Fill the three beakers with cold water

2. Fold over the bottom of the dialysis bag twice and place a clamp at the bottom of a single dialysis bag

3. After opening the dialysis bag pour the two test tubes of NaCl solution into the bag.

4. Remove air from the bag then close the top of the bag with a clamp after folding the bag over two times.

a. Be careful not to get any of the solution on the outside of the bag!

5. Dry the bag off with a paper towel and then weigh the bag and solution.

6. Place the bag with the NaCl solution into the beaker of water.a. Make sure the entire bag is under water

7. Repeat steps 2 through 6 using the Glucose solution

8. Repeat steps 2 through 6 using the Starch solution

9. Leave the bags sit in the beaker for 1 hour.

10. After 1 hour remove each bag from the beaker and dry.

11. Weigh each bag and record the weight.

Weight for NaCl bag:Before:____________________________ After sitting in Beaker: _____________________

Weight for Glucose bag:Before: ___________________________ After sitting in Beaker: _____________________

Weight for Starch bag:Before: ___________________________ After sitting in Beaker: _____________________

NaCl:1. Using a dropper, measure out 5-ml of fluid from the beaker containing the

NaCl dialysis bag and put into an empty test tube.2. Using a dropper, measure out 5-ml of fluid from the dialysis bag

containing the NaCl solution.3. Add 2-3 drop of Silver Nitrate (AgNO3) in both test tubes. A white

precipitate indicates positive of NaCl.

Was NaCl present in the sac? _____________

Was NaCl present in the beaker? ______________

Glucose:

1. Using a dropper, measure out 5-ml of fluid from the beaker containing the Glucose dialysis bag and put into the test tube containing blue Benedict’s solution.

2. Using a dropper, measure out 5-ml of fluid from the dialysis bag containing the Glucose solution and put into a second test tube containing blue Benedict’s solution.

3. Place the two test tubes into a hot water bath and leave the test tubes for approximately 15 minutes.

4. A rusty precipitate forms, the test is positive for glucose.

Was Glucose present in the sac? _______________________

Was Glucose present in the beaker? _______________________

Starch:1. Using a dropper, measure out 5-ml of fluid from the beaker containing the

Starch dialysis bag and put into an empty test tube.2. Using a dropper, measure out 5-ml of fluid from the dialysis bag containing

the Starch solution and put into an empty test tube.3. Add 2-3 drop of Lugol’s Iodine in both test tubes. A blue/black precipitate

indicates positive of Starch

Was Starch present in the sac? _______________________

Was Starch present in the beaker? _______________________

Questions:

1. In which of the solutions did net osmosis occur? ____________________________

2. In which solution did net simple diffusion occur? ____________________________

3. A semipermeable sac containing 10% NaCl, 5% Glucose, and 8% Albumin is suspended in a solution with the following composition: 8% NaCl, 11% Glucose and 30% Albumin. Assume that the sac is permeable to all substances except albumin. State whether each of the following will (a) move into the sac, (b) move out of the sac, or (c) not move.

Glucose: __________________ Albumin: _______________________

Water: _____________________ NaCl: ___________________________

4. Characterize membrane transport as fully as possible by choosing all the phrases that apply and inserting their letters on the blanks.

Passive processes: ___________________________ Active processes: ____________________

a. account for the movement of fats through the cell membraneb. explain solute pumping, phagocytosis and pinocytosisc. includes osmosis, simple diffusion and filtrationd. may occur against the concentration gradiente. move ions, amino acids and some sugars across the cell membrane

5. Define the following terms.

Selective permeability: ______________________________________________________________________

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Diffusion: _____________________________________________________________________________________

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Simple diffusion: _____________________________________________________________________________

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Facilitated diffusion: ________________________________________________________________________

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Osmosis: _____________________________________________________________________________________

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Filtration:

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Endocytosis: _________________________________________________________________________________

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Exocytosis: ___________________________________________________________________________________

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