Activity: Diffusion – What Is It?

Goals:

  1. To demonstrate how diffusion of molecules takes place from areas of higher concentration to areas of lower concentration.
  2. To observe diffusion of vegetable dye occurring in a cup of water.

Background Information: Diffusion is the movement of molecules of a substance from where they are in higher concentration to where they are in lower concentration. You can experience diffusion by spraying air freshener in a room. The molecules of the fragrance will move from the container into the surrounding air until the air freshener molecules have reached equilibrium or a balanced distribution throughout the room.

Diffusion depends on the fact that molecules of gases and liquids are always moving. Understanding diffusion is important to learning about the movement of molecules in and out of cells.

Materials: food flavoring extracts (peppermint, vanilla, or citrus), beakers or small plastic cups, vegetable dye, colored pencils, water

Procedure:

What I Know: Have you ever had an experience where you could smell something long before you got to where the smell was coming from? How about entering your house and knowing exactly what was cooking in the kitchen. What about smelling the odor of a skunk from inside your house when you know the skunk is outside? Write a few sentences about your experiences with diffusion.

Part 1: A Balloon as a Cell Model

  1. At your tables there will be balloons. A cotton ball saturated with a food flavoring was placed in these balloons. Each balloon was then blown up and knotted.
  2. Pick up the balloon and see if you can identify the fragrance that was placed in the balloon.
  1. Using arrowsshow the direction of the molecules of fragrance.

Part 2: The Process of Diffusion

First read through all the directions in this part.

  1. Add water to a cup.
  2. Place a drop of vegetable dye in the cup and immediately observe what happens to the dye.
  3. Using a colored pencil, complete the drawing of the cup in the first box to reflect your observations.
  4. After about 1 minute, observe what happens to the food dye in your cup.
  5. Using colored pencil, complete the drawing of the cup in the second box to reflect your observations.
  6. After about several minutes observe what happens to the food dye in your cup.
  7. Using a colored pencil, complete the drawing of the cup in the third box to reflect your observations.
  8. Describe what happened to the food dye in the caption box under your picture. Use the words, diffusion, many, few, and molecules in your caption.
  9. Make an illustration of your observations showing the water and cup set-up immediately after adding the food coloring, one minute after adding the food coloring and several minutes after adding the food coloring.
  10. Make your observations by looking at the cup sideways at eye level.

A drop of food coloring is placed in a cup of water. / The food coloring in water after about 1 minute. / The food coloring in water after several minutes.

Caption:

  1. What I Did: Write a summary of the procedure you used for each part of this activity.

Part 1:

Part 2:

  1. What I Wonder: Pose a why or how question about what you would still like to know about the topic of diffusion.
  1. Questions: Answer the following questions in complete sentences. Refer to pages 40 – 41 in your text book.
  1. Describe what it means when we say that a cell is selectively permeable?
  1. Name the three ways that substances can move in and out of a cell.
  1. Define diffusion.
  1. What I Learned: Write four or five sentences describing what you learned from the activities. Be sure to include examples from your observations to provide evidence for your explanations.