Integrated Science
Name ____________________________
Cell Membrane and Bubbles Lab
Background: The cell membrane is a dynamic and complex structure that surrounds the stuff
inside the cell. The cell membrane regulates the cell to cell interactions and the cell to
environment interactions (that is, as a “gatekeeper,” it decides what goes in and out).
The lipid molecules that make up a cell membrane are very similar to soap bubbles. The soap
bubble is made up of lipid molecules which contain a long hydrophobic (water hating) tail and a
hydrophilic (water loving) head. The cell membrane is made of a double layer of lipids!
When the water-loving and water-hating molecules are mixed in water, they immediately put
their hydrophilic head in the water and the hydrophobic tails out of the water. In soap bubbles, a
double layer forms because the heads will join with the water while the tails will stick outward
towards the air. The cell membrane is just backwards – heads out and tails in!
The lipid double layer of cell membranes and soap bubbles explain several important
properties. Do the procedure to explore some of these properties.
Procedure
1. Flexibility The lipid double layer is basically a fluid arrangement where the molecules can
move freely about in the plane of the double layer. Flexibility is characteristic of the soap
bubble. A cell membrane is actually even more flexible since it has a lower surface tension.
Show flexibility with your bubble holder. Describe or draw what you did below.
Question: Why is a cell membrane even more flexible than the soap bubble?
2. Self-sealing If you cut a soap bubble in half, you get two bubbles rather than two half
bubbles. If two bubbles bump into each other, they join and form a bigger bubble. It is
possible to have fission and fusion of lipid double layers. The same is true of cell
membranes! Because the cell membrane is supported by cell structures on one side and a
water environment on the other side, cells do not fuse with neighboring cells.
Show that the bubble is self-sealing.
Make a domed bubble in the bubble solution by blowing into it. You should be able to put
soapy materials through the bubble without popping it (like a finger). Next, try to cut the
bubble in half. Join two domed bubbles by letting them touch.
Describe what you did and what happened below.
Question: Why don’t our cells fuse in our body?
3. A cell membrane keeps some materials out of the cell and lets other things inside. Some
molecules go through because proteins actively move them in or out. Show that the cell
membrane can have proteins move around by putting different substances into your soap
bubble and moving them around. (pencil, paperclip, etc)
Describe what you did and what happened below.
4. The cell membrane also has openings called pores through which some molecules pass.
Show pores by tying a piece of thread into a circle and place it onto the soapy film Pop
the film inside the circle. Move the circle around with your finger.
Describe what you did and what happened below.
SUMMARY QUESTION:
5. What is the structure of the cell membrane and what unique properties does it have?