Movement Across the Membrane (Diffusion)

Kelly Ludwig                   Lincoln-Way High School
                               1801 East Lincoln Highway
                               New Lenox IL 60451
                               (815)485-7655

Objectives:

     This lesson is designed for a high school student. The main objectives of 
this Mini-teach are to explain the concept of diffusion and to show the process 
how all materials enter and leave the cell. 

Materials Needed:

          food coloring                  water
          beakers                        air freshener/perfume
          sugar cube                     test tube
          phenolphthalein                cellophane
          rubber band                    ammonia
          raisins                        toothpick
          paper towel                    dialysis tubing/cellophane baggie
          starch                         iodine
          paper clips                    paper cups

Strategy:

                                    DIFFUSION

Activity #1
 1.  Place one drop of food coloring into a beaker of water. 
 2.  Observe what happens for 2-3 minutes.

Activity #2
 1.  Spray perfume/air freshener at the back of the room.
 2.  Observe what happens for 2-3 minutes.

Activity #3
 1.  Fill a cup with water.  Gently touch the surface of the cup of water.
     Taste the water.
 2.  Drop a sugar cube in the water.
 3.  Taste the water every 15 seconds.

                          MOVEMENT ACROSS THE MEMBRANE

Activity #1
 1.  Fill a test tube 1/2 full with water.
 2.  Add 2-3 drops of phenolphthalein to the water.
 3.  Wrap a piece of cellophane over the mouth of the test tube.  Secure it with  
     a rubber band.
 4.  Turn the test tube over an open bottle of ammonia.

Activity #2
 1.  Obtain a soaked raisin and an unsoaked raisin.  Carefully blot the raisins 
     dry.  Do not break the skins.
 2.  Use a toothpick to poke a hole in one end of each raisin.
 3.  Gently squeeze both raisins.

Activity #3
 1.  Obtain a piece of tubing (a cellophane baggie could be substituted).  Tie a 
     knot at one end then fill it 1/4 with water.
 2.  Make sure the tube does not leak.  Empty the water out of the tubing.
 3.  Add 3 teaspoons of starch to the tubing.
 4.  Squeeze the air out of the tubing.  Tie a knot at the open end.
 5.  Wash off the tubing.
 6.  Fill a beaker 3/4 full with water.  Add 10 to 15 drops of iodine and stir.
 7.  Tie a paper clip around each knot in the tube.  Hang the tube in the beaker 
     of water.

Performance Assessment:

     At the conclusion of the Mini-teach, students will be able to answer the
following questions:
 1.  Describe what happened to the drop of food coloring/air freshener 
     molecules?
 2.  How do molecules move?
 3.  What is diffusion?
 4.  What happened to the taste of the water?
 5.  What caused the taste of the water to change?
 6.  What happened to the liquid in the test tube?
 7.  Where was there a high/low concentration of ammonia.
 8.  Which way did the ammonia move? (Use the word "concentration" in your 
     answer)
 9.  Explain how gases are exchanged between the respiratory system and the 
     circulatory system.
10.  How do gases pass out of the lungs into the capillaries?
11.  How do the soaked and unsoaked raisins differ?
12.  What do you think is coming out of the raisin, how did this liquid get
     into the raisin?
13.  What does the skin of the raisin represent?
14.  What happened to the starch?
15.  What happened to the iodine and water?
16.  Explain the movement of materials across the tubing.
17.  Explain how foods are exchanged between the digestive system and the
     circulatory system.
18.  How is the tubing like a membrane?
19.  How does digested food pass out of the intestine into the capillaries?
20.  How do materials enter and leave the cells?

Conclusion:

     Students will understand the process of diffusion and its role in
moving materials across the membrane.