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What is a membrane?  Can you think of an example?  
Covered Food Image
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Does you mother ever put plastic wrap around left over food? .... or over a dish of leftovers?  You could think of the plastic sheet as a membrane.  The plastic wrap has two characteristics of cell membranes:

1) it is thin
2) it restricts what can go through it.

In a living cell, the membrane must let some substances pass from the outside to the inside of cells and other substances to move in the opposite direction. But the most obvious thing a membrane does is to   keep bulky materials inside the cell.  You could say that the membrane helps hold things together, but cell membranes do more than that. 

  

Tennis Ball Image

Can you think of something familiar that is like a cell with a membrane around it?  An even better comparison would be a tennis ball, because the fuzz on a tennis ball can be compared with large molecules of proteins  and complex sugars that are found stuck through the outer membrane.
Membranes are everywhere - around cells and surrounding
structures inside of cells
After completing this lesson, each student should be able to:
  • Define the structure and function of a cell membrane.
  • Identify the molecules of a membrane, including the locations of their electric charges.
  • Explain why membranes can form all by themselves
  • Understand what the toxicant alcohol does to the cell membrane.
cellmembranes.jpg (654257 bytes)

High magnification of part of a cell, showing that it contains many components.

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