Movement Across the Membrane (Diffusion)

Kelly Ludwig Lincoln-Way High School
1801 East Lincoln Highway
New Lenox IL 60451


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


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
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
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?


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