Download Lab Cell membrane bubble

CELL MEMEBRANE STRUCTURE AND FUNCTION
The cell membrane is a double layer of phospholipids molecules with protein molecules sticking through it. Some of these
proteins act as proteins channels to help move substances into and out of the cell.
QuickTime™ and a
decompressor
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Each phospholipid molecule has a polar (LOVES water) head and 2 non-polar (HATES water) tails. For all cells, the
plasma (cell) membrane forms a boundary between the living cell and its surroundings and controls the traffic of
molecules into and out of the cell. It allows some substances to cross more easily and blocks passage of some
substances completely; for this reason we call the plasma (cell) membrane) semi-permeable or selectively permeable.
They are arranged like this:
(Loves water)
QuickTime™ and a
decompressor
are needed to see this picture.
Tails
(Hates water)
Heads
A soap bubble has a similar design, so soap bubbles can be used to understand some of the properties of the cell
membrane…YEAH!!!
MATERIALS:
 Square plastic plate to hold bubble solution
 Square template of straws and string – the cell membrane 
 Toothpick
 Circular hair tie
 Paperclip
 Clear tubing – protein channel
PROCEDURE: MAKING THE CELL MEMBRANE
• Your teacher will fill your plate with half an inch of soap solution.
• Holding onto the straw handles of your cell membrane template, dunk the template into the
soap solution.
• Raise your template out of the pan and allow the excess soap to drop off.
• Hold your “bubble” membrane up to show the following things a membrane can do.
*WRITE ALL ANSWERS IN YOUR COMPOSITION BOOK. USE COMPLETE SENTENCES. NUMBER YOUR
ANSWERS*
PART A: FLUIDITY
DEFINE:
 Selectively permeable
 Fluid Mosaic
 Phospholipids
 Hydrophobic
 hydrophilic
The “Fluid Mosaic Model” of the cell membrane means that the cell membrane is made up of many small molecules. Each
one is moving around and changing position constantly.
TO SHOW THIS:
Let the lights shine off the bubble surface. Look at the movement you see within the bubble.
A1. What are these soapy molecules doing?
________________________________________________________
PART B: FLEXIBILITY
Within the membrane, molecules can move freely around and reorganize themselves into almost any sort of shape.
TO SHOW THIS:
• Make a new cell membrane
• Twist your cell template in opposite directions into different shapes.
B1. What happens to the soapy film? ______________________________________
PART C: SELF-SEALING
DEFINE:
 Exocytosis
 Endocytosis
Two Types of Endocytosis:
 Phagocytosis
 Pinocytosis
• The CELL membrane is NOT solid. Some small molecules can pass through it.
• Make a new cell membrane
• Take a paper clip and pass it through the cell membrane.
C1. What happens? ___________________________________________
Make a new cell membrane using your template. This time, dip the paperclip into the soapy solution first! Pass the paper
clip through the soapy membrane to the other side.
C2. Did the membrane seal around the object? _________________________________
C3. Why do you think the paper clip must be coated with soap in order to pass through the membrane?
Relate the concept of semi-permeable (selectively permeable) to your results.
Place the circular hair tie onto the surface of the bubble cell membrane. With your finger, pop the bubble surface inside
the hair tie. Gently pull the hair tie to one edge of the cell membrane, until you pull the hair tie off the surface of the cell
membrane.
C4. Does the bubble seal as you pull the hair tie off of the surface? Why? Explain using the
Concepts of exocytosis and endocytosis. Draw an example of the process.
PART D: TRANSPORT PROTEINS
DEFINE:
 Protein channel
 Facilitated diffusion
 Active transport
 Passive transport
Small molecules, like water, can sometimes move into the cell through small holes in the cell membrane. Larger
molecules cannot do this. They need to go through channels made by protein molecules in the membrane.
TO SHOW THIS:
• Take a small piece of rubber tubing
• Make a new cell membrane
• Carefully stick the rubber tubing halfway through the soapy membrane …CONGRATULATIONS,
You made a model of a transport protein in a cell membrane
 Pass a toothpick through the “protein channel.”
D1. What type of cell transport does this represent? Explain.