**Procedure:**

1. Put on your lab apron and goggles.
2. Cut two strips of dialysis tubing (about 15 cm long) and soak them in a beaker of tap water for approximately 2 minutes.
3. Rub the dialysis tubing between your fingers to find an opening. Tie a knot near one end of the dialysis tubing. Repeat with the other piece of tubing.
4. Using a graduated cylinder, measure 15 mL of the 4% starch suspension. Pour the suspension into the open end of one of the dialysis tubes through a funnel.
5. Fill the second dialysis tube with 15 mL of the glucose solution.
6. Twist the open end of each dialysis tube and tie a knot. Try to have as little air as possible. Trim off the excess tubing.
7. Rinse the outside of both dialysis tubes with distilled water to remove any fluids that may have leaked out during the tying process.
8. Cut two equal lengths of string. Suspend each tube with string from a ring clamp.
9. Pour 250 mL of water into a small beaker. Add 5 drops of Lugol's solution.
10. Pour 245 mL of the dilute Lugol's solution into a large beaker, and test the solution for the presence of glucose using a glucose indicator.
11. Suspend the dialysis tubes in the dilute Lugol's solution so that they are submerged but do not touch the bottom of the beaker.
12. Pour the remaining 5 mL of dilute Lugol's solution into a test tube and place it in the beaker with the dialysis tubes.
13. Pour 5 mL of the starch suspension into a second test tube and place it in the beaker. Wait for 20 minutes.
14. While waiting, construct a table similar to Table 1 in your notebook. Record your observations in the second column.
15. After 20 minutes, complete the third column of your table.
16. Test the dilute Lugol's solution in the beaker and test tube for the presence of glucose. Indicate the color the glucose indicator changed. Add this information to your table.
17. When you have finished, empty the contents of the dialysis tubes down the sink drain, flushing with plenty of water. The empty tubes may be placed in the garbage. Be sure to wash the equipment and your hands thoroughly.

**Analysis:**

(a) Which substance diffused from the dilute Lugol's solution in the beaker into the dialysis tube? Provide laboratory evidence and suggest a reason to explain this.

(b) Which substance diffused from the dialysis tube into the dilute Lugol's solution in the beaker? Provide laboratory evidence and suggest a reason to explain this.

(c) Explain the function of the test tube with Lugol's solution. What evidence does it provide?

(d) Explain the function of the test tube with the starch suspension. What evidence does it provide?

(e) What properties does this experiment demonstrate about the dialysis tube as a model for a cell membrane?

(f) Which substance tested has the largest molecules? Explain your answer.

**Evaluation:**

(g) Suggest possible sources of error in the procedure.

(h) Prepare a report.

**Observations:**

- **Initial:**
- Dilute Lugol's solution: Slightly yellow in beaker
- Starch suspension in dialysis tube: White + opaque
- Glucose solution in dialysis tube: Colorless + clear
- Dilute Lugol's solution in test tube: Slightly yellow
- Starch suspension in test tube: White + opaque

- **After 20 mins:**
- Dilute Lugol's solution: Slightly yellow
- Starch suspension: Dark blue + plumped tube
- Sugar observations:
- Initial/before 20 mins: No glucose in beaker
- After 20 mins: Glucose in beaker
- No change to substances inside the test tubes