Grade Level: 9th - 12th; Type: Life Science
- To build a model of the cell membrane.
- To investigate how the cell membrane regulates what moves into and out of cells.
- What molecules of the cell membrane do the cotton swabs represent?
- If a molecule needs to enter or exit the cell and it cannot fit between the phospholipids how can it cross the membrane?
The cell membrane is a barrier that separates a cell from the external environment. It controls the passage of materials into and out of the cell. The membrane is made up of a double layer of phospholipids, called the lipid bilayer. Scattered between these phospholipids are various other molecules such as protein channels, pumps, cholesterol, and carbohydrate chains. With the cooperation of the phospholipids and other embedded molecules the passage of molecules into and out of the cell is controlled. Think of the cell membrane as the exterior walls and roof of your home. It’s scattered with a number of windows, doors and vents. Just like the cell, these items help to control what enters and exits your home.
- 3 pipe cleaners of different colors
- 1 regular-sized drinking straw
- Thick, medium-size rubber band
- Approximately 50 cotton swabs
- 1 marble
- 1 BB
- Gather the cotton swabs into a bundle and place the rubber band around the middle to keep them in a bundle.
- Place a receptor molecule into the cell membrane.
- Take one of the pipe cleaners and place it through the bundle of cotton swabs.
- Bend one end of it into a circular shape. This shape represents how signal molecules bind to specific molecules. Only a circular-shaped molecule can bind with this receptor.
- Use the second pipe cleaner as a carbohydrate chain. Place it in the bundle of cotton swabs, just as in step 2. Don’t bend this pipe cleaner.
- Cut your drinking straw in half. Place each half into different locations in the bundle of cotton swabs. These represent the protein channels and pumps.
- Holding the cotton swabs vertically, place the marble on top of the swabs. Does it pass between the swabs? Why or why not?
- Place the marble on top of the straw. Does it pass through the straw? Why or why not?
- Still holding the cotton swabs vertically, place the BB on top of the swabs. Does it pass between the swabs? Why or why not?
- Place the BB on top of the straw. Does it pass through the straw? Why or why not?
- Place your mouth on the cotton end of the swabs and blow. Can you feel air on the other side of the swabs? Why or why not?
- Explain how the swabs and straws actually represent the components of the a real cell membrane.
- Roll the bundle of cotton swabs between your hands. Do the individual swabs move? Without pulling the straw out can you move it between the swabs? How does this represent the fluid mosaic model?
Terms/Concepts:Cell; Cell membrane; Phospholipid; Receptor and signal molecule; Selective permeability; Protein channels; and pumps; Carbohydrate chain; Fluid mosaic model