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1. 
   lynn30k Teacher
   High School - 10th Grade

   eNotes Editor

   The plasma, or cell, membrane is one of the most important parts of both plant and animal cells. The membrane divides cells from each other. It controls what enters and leaves the cell, by both active transport, passive transport, and osmosis. Passive transport involves small molecules such as small proteins. Water moves through relatively easily with no energy expenditure. This is usually driven by relative concentrations of solutes--the water will move either in or out of the cell in order to equalize concentration between the inside and the outside of the cell.  Active transport requires an energy expenditure to move more complex molecules in or out of the cell trough the membrane.

   Sources:

   http://www.biologymad.com/cells/cellmembrane.htm

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   Posted by lynn30k on Friday October 30, 2009 at 9:10 PM
   
   

2. 
   tutorialguide

   a). Protective – It forms a protective layer around the cell. b). It exists as barrier which separates the internal structures of cell from the external environment. c). Semipermeable membrane – It acts as a semipermeable membrane allowing selective passage of substances in and out of cell. d). It links adjacent cells. e). Digestive – It takes in food and excretes waste products.

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   Posted by tutorialguide on Thursday November 19, 2009 at 7:35 PM