Mr. Vazquez Science HW Pd. 2

COPY THE INFORMATION BELOW IN YOUR LABORATORY NOTEBOOK.  REMEMBER TO USE PROPER HEADING IN  THE FIRST PAGE OF THE LAB REPORT.

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Title:  How to model a cell membrane?

Objective:   To model how cell membranes are selective by allowing some substances to pass through the membrane while rejecting others.

Materials:

Dialysis tubing                                        Lugol’s solution

Tie cord                                                    Starch solution

Plastic cups                                              Glucose solution

Glucose test strip

Procedure:

1. Soak the dialysis tubing in water for a few minutes, then work it between the fingers until the tubing opens up.
2. Tie-off one end with the tie cord (approximately 1″ from end). 
3. Pour equal parts of Starch solution and Glucose solution into the tubing  that you just prepared.  Once filled tie-off the second end with the tie cord.  Rinse the outside of the tubing to remove any traces of solution from its exterior and set aside on a clean surface. 
4. Fill the plastic cup with water to about 1″ from the top.  Use one test strip to test the water for any trace of glucose. This test should be negative as there should be no glucose in the water. 
5. Add 10 drops of Lugol’s solution to the water and stir. 
6. Place the “tubing cell” into the cup of water and allow it to stand for 5 minutes or more. 
7. Use the second glucose strip, test the water outside the cell for evidence of glucose. 
8. Record your observations 

Results / Data 

Conclusion

1. Why did the glucose strip was negative before adding the cell to the water cup?
2. Why was the glucose strip giving a positive reading for glucose in the water of the cup after adding the cell?
3. Why did the inside of the cell turn black?  What is this an indication of?
4. Did the Glucose cross the membrane?  How do you know?
5. Did the Starch cross the membrane?  How do you know?