Bubbles to Explore Cell Membranes
The Fluid Mosaic Model
Every day, single-celled organisms, as well as
multicellular organisms, must interact with their respective watery
environments. Whether it’s a paramecium surviving day to day in the
ever-changing health of local waterways, or a human’s bone tissue bathed in
blood-like fluid bringing oxygen and nutrients to the cells while removing
carbon dioxide and other wastes from the cells, all cells must have a way to
maintain a consistent internal environment.
One way to
maintain this consistency is by the actions of the cell membrane. The cell
membrane separates a cell from other cells and from its surrounding fluids. It
holds the cell together and can give shape to the cell. Membranes are not solid
barriers- certain molecules can pass through them. They are called “selectively
permeable” because some molecules are allowed to pass through, but others are
not. What types of molecules do you think
need to pass through the cell membrane?
membrane consists of two layers. It has a double layer of lipid molecules,
called phospholipids, with protein molecules embedded within the lipid bilayer.
The phospholipids and the proteins are not rigidly fixed in place – they can
move about within the membrane. For this reason, cell membranes are considered
- What is the structure of the cell
membrane and what unique properties does it have?
- How do these properties relate to how it works?
can we visualize the fluidity of a cell membrane?
GOALS: In this lab
activity, you will…
the structure of the cell membrane by creating a model.
the properties of the cell membrane.
the structure of the cell membrane to its function.
IDEAS: The important concepts and skills
covered in this activity are…
membranes consist of two layers of phospholipid molecules with proteins
embedded within this double layer.
membranes are not rigid structures. Rather, cell membranes are fluid and
dynamic. The phospholipids and the proteins may shift among each other
within the cell membrane.
Scientific Content –
order to establish and maintain their complex organization and
structure, organisms must obtain, transform and transport matter and
energy, eliminate waste products, and coordinate their internal
cell membrane is dynamic and interacts with internal membranous
structures as materials are transported into and out of the cell.
cell membrane, which is composed of proteins and two layers of
phospholipids, is selectively permeable and regulates what enters and
leaves the cell.
Scientific Process –
will make predictions and inferences based on their observations during
are no math skills or graphing skills associated with this activity.
- Draw the structure of the cell
membrane in the space below. Indicate which areas of the membrane are
hydrophobic and which areas are hydrophilic. Include proteins that are
embedded within the membrane in your drawing.
investigation, you will use bubbles to explore how a cell membrane might work
and how its structure is related to its function.
- Spread newspapers or paper towels
on top of your lab tables or work area.
- Each group will need the
following materials: 2 straws,
cotton string, cotton thread, scissors, glass stirring rod, tray, aluminum
wire 6-8 inches in length, and bubble solution (to a depth of 1-2 cm once
placed in the tray).
- Cut the straws to lengths of
15-20 cm to make 4 equal lengths.
- Put the cotton string through the
straws to make a rectangle about 3/4 of the tray size and knot the end.
Cut the excess string.
- Cut a piece of cotton string 6-7
cm in length and knot. Place this aside.
- Form a circle at the end of the
aluminum wire approximately 2-3 cm in diameter. Place this aside.
- Form a film of bubble solution on
your straw device by dipping it into the bubble solution in your tray.
Show the flexible nature of membranes by bending and folding the film.
Predict: Why might
this characteristic be important to a cell’s survival?
- Form an opening in the membrane
by floating a circle of thread on the film, popping the inside of it, and
then gently removing it by using your glass stirring rod.
What happens to the membrane? Relate this
ability to a function that a cell
must perform in order to survive.
- To demonstrate movement of proteins
within the lipid bilayer, insert a pencil or the glass stirring rod
through the membrane and move it around. Your bubble solution should not
Why might it be important for proteins to be able to move from one part
of the cell membrane to another?
- Demonstrate how a eukaryotic cell
could “evolve” from a prokaryotic cell using the aluminum “magic wand” and
your straw device. (Hint: You must
float a bubble within a bubble.)
Infer: How does this represent how eukaryotic
cells may have evolved from prokaryotic cells?
The cell membrane is not the only membrane consisting of a
double layer of phospholipids. Research other phospholipid bilayers and their
use or function and present your findings to the class.
Compare and contrast soap bubbles and
cell membranes with regard to structure and function.
what you have learned…
While on a hunting trip in a remote
location in Delaware,
a friend of yours was bitten by a copperhead. He nearly died from hemolysis, or
breakage of many of his red blood cells. The copperhead’s venom was sent to a
lab and the lab technician found three different enzymes present:
phospholipase, which breaks down phospholipids; neuraminidase, which removes
carbohydrates from cells; and protease, which degrades proteins. Which of these
enzymes do you think was responsible for his near fatal red blood cell hemolysis?
Explain your reasoning.