Biology 2201
Passive Transport/Osmosis Core Lab
Name:_____________________________
Mark: ____/20 = ______
Purpose: To demonstrate the movement of molecules by diffusion and osmosis.
Materials:
Dialysis tubing
Glass tube
2 beakers
Stand and clamp
Iodine
Water
Medicine dropper
Starch solution
Elastic band
Felt marker
Procedure:
1. Fill one beaker with water and the other ¼ full of starch solution
2. Soak a strip of dialysis tubing in the beaker of water for 1 min. Rub it gently between your
thumb and index finger until it opens.
3. Tie a knot at one end, and pull from both ends to secure the knot.
4. Fill the dialysis tubing with starch solution and insert the glass tube into it. Make sure the glass
tube is not chipped or sharp!
5. Secure the top of the dialysis tubing around the glass tube by tying it with the elastic band
6. Gently rinse any starch off the outside of the dialysis tubing using a gentle stream of water from
a faucet.
7. Place the dialysis tubing in a beaker of water until the starch solution moves up the glass tube to
a point above the top of the dialysis tubing. Immersing more of the dialysis tubing in the water
forces the starch solution to move up the glass tube.
8. Attach the glass tube to the stand with the clamp and mark the initial height of the starch
solution with a felt marker.
9. Add about 10 drops of iodine to the beaker of water; the water should turn orange. If you see a
blue black color, that means the dialysis tubing was not rinsed properly or the tubing is leaking.
(Starch turns black in the presence of iodine). Correct the problem, place the apparatus in
another beaker of water, and check again for leaks.
10. Allow the apparatus to sit for 10 minutes.
Data: (2)
Color before Immersion
Color after 10 min Immersion
Starch inside bag
Water/Iodine in beaker
Analysis:
1. In this lab, which substances move by diffusion and which by osmosis?
Diffusion:_________________________________________(1)
Osmosis:_________________________________________(1)
2. The dialysis tubing provides us with a model of a cell membrane. Like a living cell
membrane, it allows some substances to pass through its pores, but prevents the
passage of others. Based on your lab data, draw a diagram indicating which molecules
are permeable through the dialysis tubing. Provide reasons for your answers.
Diagram: (use appropriate colored pencils to show movement)(3)
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3.
Does the movement of materials in and out of the dialysis tubing differ from that of a
real cell membrane? Explain. (3)
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4. What evidence do you have that the dialysis tubing is permeable to water? (2)
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5. What other substance(s) was/were permeable?(1) _____________________________
6. Which substance(s) were impermeable across the membrane? (1)__________________
CONCLUDE AND APPLY:
7. Based on your knowledge of osmosis, predict how the use of road salt to melt ice or
snow affects the plants bordering the sidewalk, road, or highway. Explain. (3)
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