Phospholipid Bilayer
The phospholipid bilayer consists of two adjacent sheets of phospholipids, arranged tail to tail. The hydrophobic tails associate with one another, forming the interior of the membrane. The polar heads contact the fluid inside and outside of the cell.
Source
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"OpenStax College, The Cell Membrane. October 23, 2013."
http://cnx.org/content/m46021/latest/
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