General ---------Biology----------------------------------------------------- ------------------Online-------------------------------- Ch. 8 Membrane Structure and Function

Ch. 8 is about the cell membrane and how chemicals move through the membrane as they move into and out of the cell.  Oxygen, carbon dioxide and water can diffuse directly through the lipid bilayer, but most other molecules must pass through a protein gate or channel. 

The plasma membrane separates the living contents of the cell from the non living surroundings.  Structurally, it is composed of phospholipid molecules arranged in two layers called a "lipid bilayer."  Functionally, the membrane regulates the passage of molecules into and out of the cell.

Phospholipid oil when poured onto the surface of water forms a thin film one molecule thick.  When agitated, this phospholipid layer self assembles into oil droplets  (micelles).  Some of these droplets contain water inside (liposomes) and resemble cells. 

Cells may have evolved from liposomes and similar proteinoid spheres that can arise spontaneously under certain conditions.  The current theory of how cells may have evolved from these structures is discussed in Ch. 26.