• The plasma membrane (also known as the cell membrane) forms a barrier between the cytoplasm inside the cell and the environment outside the cell.
  • It allows only certain substances to pass through, while keeping others in or out.
  • To understand how the plasma membrane controls what crosses into or out of the cell, you need to know its composition.
  • The plasma membrane is composed mainly of phospholipids, which consist of fatty acids and alcohol.
  • As shown in the Figure below, each phospholIPid molecule has a head and two tails.
  • The head “loves” water (hydrophilic) and the tails “hate’ water (Hydrophobic)
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