Prelab This Must Be Completed Before the Lab Is Conducted!

Name ______

Prelab – This must be completed before the lab is conducted!

Beaker ABeaker B

To the Beakers A & B, indicate what goes into each solution and goes into each of the bags

1.How do you open up the cellulose tubing and how is it set up?

2.What goes into the two cellulose tubing bags?

Tubing A

Tubing B

3.What goes into Beaker A?

4.What color should Beaker A be?

5.What goes into Beaker B?

6.How long will the two Beakers sit for? ______

7.How do we test to see if glucose diffused through the cellulose tubing into Beaker B?

Name ______Due Date ______

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Investigating the Movement of Molecules through a Membrane

How do molecules get in and out of cells? In this investigation, you will use a model of a cell membrane (cellulose tubing) to observe the ability of molecules (glucose, starch, water and iodine), to move in and out of a cell.

Procedure:

1. Label two plastic cups, “A”“B”. Fill the two plastic cups with water up to the bottom ridge line.
2. Add 10 drops of iodine to Cup “A”
3. To open the cellulose tubing, first moisten it. Then rub it between your thumb and forefinger. Tie a tight knot about 1cm from one end of each piece of tubing.
4. Into tubing “A”, put 20 mL of starch solution into it. Twist the top of the tubing and fold it over. Then put the foam clamp on it. Rinse the tubing well to remove any starch that may have spilled onto the sides.
5. To tubing “B”, put 20 mL of glucose solution into it. Repeat the same procedure as in #4.
6. Put tubing “A” into cup “A”, and tubing “B” into cup “B”. Wait 15 - 20 minutes.
7. After 20 minutes, observe any color change to either the water/iodine solution in cup “A” or also any color change in tubing “A”. Record your observations on the data table
8. To cup “B”, place a Glucose test strip into the water. Leave it there for 10 seconds and then take it out. Wait 2 minutes and record if the color changed or not with a + or – in the data table. Any color other than the original color is a positive test for glucose. Record your observations on the data table as being either a positive or a negative result for glucose
9. Save cup “B” overnight in the designated place. Be certain that your name is on the cup.
10. Empty cup “A” and rinse it off. Take the foam clamps off and place it on the lab table with the cups. Throw the cellulose tubing in the garbage.
11. After a day, observe the size of tubing “A” and note any change in size.

Discussion – It should go without saying but all answers must be in complete sentences.

1. What did the “bags” and the cellulose tubing represent?
2. What must be the condition of the “bags” in order for molecules to diffuse through them?
3. On the basis of the chemical test for starch, what must have happened to the iodine molecules in cup “A”?
4. On the basis of the chemical test for glucose, what must have happened to the glucose molecules in cup “B”?
5. From the evidence obtained by allowing cup “B” to stand overnight, what other substances must have passed through the membrane in cup B?
6. Which substance did not pass through the membrane and explain how you knew that it did not.
7. What conclusion could you make about the size of the iodine, glucose, starch and water molecules in relationship to membrane?

This should be typed up in the order which is given on the next pages. Both members need to participate in the write-up for complete credit.

Name______Due Date ______

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Title of the lab:______

Purpose:______

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Hypothesis:______

Data Table: Molecular Movement through a Membrane Results

Discussion Questions: # 1 – 7 - To be answered in full, complete sentences.

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