Mystical Membrane

Lester,Debra
                          

Objectives

1)  Students will be able to explain Osmosis and Diffusion. 
2)  Students will observe diffusion  using a semi-permeable membrane.  
3)  Students will list examples of diffusion.  

Equipment and Materials

1 semi-permeable membrane
1 plastic cup
2 Glucose Testing Strips

Recommended Strategies                  

     Have students observe a positive test for glucose and starch.  If glucose is 
present, the Test Strip will change from yellow to green. A positive test for starch 
is a blue/black color. 
 
     Have students observe a drop of food coloring added to a beaker of water. 
Discuss the observations. Using cologne, spray a small amount into the air; 
discuss the diffusion of the cologne particles. Fill a plastic cup with water.  
Test the water for the presence of glucose by dipping the yellow end of the 
Glucose Test Strip in the water.  Remove the strip and observe. Add 35 drops of 
iodine or Lugol's solution to the cup of water. Set aside for later use. Tie a 
knot in the membrane at one end . In the other end put 3 cm3 of starch and 3 cm3 
of sugar.  Rinse the bag thoroughly to remove any glucose or starch. Mix the 
contents together. Place the filled membrane into the cup of water with the 
Lugol's (iodine) solution.  BE CAREFUL NOT TO SPILL THE CONTENTS INTO THE CUP. 
After 5-10 minutes look at the contents. 

     Have students make the following observations:.

        a.  What happened to the iodine in the experiment? 
        b.  What happened to the the starch?
        c.  What happened to the glucose?
        d.  What materials have diffused through the membrane?
        e.  How was this proven?
        f.  What substances did not diffuse through the membrane?

Note:   You may wish to use these questions or some of your own.