Background: Kidney dialysis machines, like the kidneys, work by filtering substances through membranes. To treat a patient whose kidneys do not function properly, his or her blood is passed through a dialysis tube that is submerged in a special solution that promotes diffusion.
The dialysis tube contains small pores that allow some substances to pass in and out of the blood depending on their molecular sizes and concentrations. For each patient treated through dialysis, a unique solution in which to submerge the dialysis tube is prescribed.
In today’s lab, you will make a model of the filtering portion of a kidney dialysis machine using dialysis tubing.
Materials: (per pair)
1 piece of dialysis tubing
One boiling tube
Iodine solution
4 glucose strips
Unknown solution A, B and C with droppers
White tile
One Wash bottle
Goggles
Procedure:
1. Starch Test
a. Stir solutions A, B, and C before starting.
b. Place a drop of solution A, B and C onto three separate corners of the white tile (be careful
not to allow the solutions to mix).
c. Add a drop of iodine onto each solution.
d. Observe for any colour change.
Solution
|
Iodine
|
A
|
Blue-Black
|
B
|
Remains Yellow
|
C
|
Remains Yellow
|
2. Glucose Test
a. Dip a glucose test strip into the solution A and wait about 30 seconds to see if there is a
color change. Compare with the colour chart on the glucose strip container to see if there is
glucose present.
b. Repeat step (a) for solutions B and C. Observe for any colour change.
Solution
|
Glucose Test Strips
|
A
|
Blue
|
B
|
Brown
|
C
|
Remains Green
|
Solution
|
Iodine
|
Glucose Test Strips
|
Starch
|
Blue-black
|
Remains blue/dark blue
|
Glucose
|
Remains yellow
|
Green/Brown
|
Water
|
Remains yellow
|
Remains blue
|
Refer to the table above and on the basis of your results, what are unknown solutions A, B, and C?
Unknown A = Starch
Unknown B = Glucose
Unknown C = Water
3. Testing for diffusion across a partially permeable membrane
a. Follow all directions/steps in the order shown. Record all observations, results and answers
to questions as directed. Notify teacher of spills or problems immediately.
b. Remove a dialysis tube from the beaker of water. One end is tied to form a knot. Rub the
open end between two fingers (be gentle to prevent tears)until the tube is open.
d. Fill the dialysis bag with approximately 2 ml of solution A; solution B; and solution
C until the bag is no more than one-half full. See Figure 1.
e. Important precaution: Thoroughly rinse the outside of the dialysis bag with water from the
tap while holding the open end tightly.
f. Half-fill the boiling tube with clean water from the wash bottle. Carefully dip the bag into the
boiling tube, ensuring that the solutions inside the bag are completely immersed.
g. Use caution to prevent the open end of the bag from slipping into the boiling tube.
h. Place about 30 drops of iodine into the water in the boiling tube. Leave the dialysis bag
soaking in the boiling tube for 10 minutes.
i. After 10 mins, gently stir the water in the boiling tube with a dropper and then place a drop of
the water onto a white tile and test for starch.
j. Dip a glucose test strip into the water in the boiling tube and wait about 30 seconds to see if
there is a color change.
Answer the following questions:
1.You know the inside of your dialysis bag contains glucose. Did glucose exit? Explain how you know this.
Yes. When the glucose test strip was put into the iodine solution, it turned brown just like solution B, which we know is glucose. This shows that glucose was present in the boiling tube after the experiment.
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2.You know the water in the boiling tube contains iodine. Did iodine enter the bag? Explain how you know this.
Yes. Iodine entered the bag and came into contact with the starch solution, so it turned blue black. If it had not entered the bag, the solution inside the bag would not have turned blue black.
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3. You know the inside of your dialysis bag contains starch. Did starch exit? Explain how you know this.
Starch did not exit. When the test for starch was carried out on the iodine solution in the boiling tube, the iodine did not turn blue black, indicating that starch was not present.
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A patient is being treated with a kidney dialysis machine. The diagram below represents the patient’s blood flow through the kidney dialysis machine. People who suffer from kidney failure have toxins accumulate in their blood because their kidneys are not filtering their blood properly. If their blood is not cleansed, they will likely die.
Kidney Dialysis Machine
Using what you learned from performing this task and your knowledge of biology and diffusion, describe how the process of dialysis cleans a person’s blood.
The kidney dialysis machine acts like the dialysis bag in the experiment. During kidney dialysis, the toxic in the blood passes through the dialysis tube and exits it, similar to how the glucose diffuses out of the bag in the experiment. Treatment solution enters the blood through the dialysis tube, similar to the iodine entering the bag in the experiment. This clears the toxic substances from the blood, enabling blood flowing out of the tube to be clean for the patient.
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