Review for Test on the Plasma Membrane
(Chapter 3 sections 3-5)
Be able to define selective permeable and explain how the selective permeability of the plasma
membrane is necessary to maintain homeostasis of the cell. (Be able to define homeostasis).
Understand the following information regarding the plasma membrane (also known as cell
membrane):
 surrounds all cells
 is composed primarily of phospholipids, with some embedded proteins and other
molecules.
 controls what materials can enter and exit the cell
o is selectively permeable
o has specific channels to allow needed materials into the cell that can’t pass
through the phospholipid membrane
Know the basic structure of a phospholipid molecule:
 phosphate group forms polar end of molecule
 2 fatty acid tails (nonpolar)
Be able to make a simple diagram of a phospholipid molecule and explain which part of the
phospholipid molecule is hydrophobic and which part is hydrophilic
Be able to explain that the phospholipids are arranged bilayer (double layer) in the membrane.
Be able to diagram the orientation of phospholipids in plasma membrane bilayer:
 phosphate groups face outward
 lipid tails face interior of bilayer
Know some possible functions of membrane proteins:
 channels to allow transport of certain molecules
 markers for cell-to-cell recognition
 receptors that receive signals from hormones etc.
Be able to define diffusion and osmosis.
Be able to define hypertonic, hypotonic and isotonic solutions.
Be able to determine which direction water will move when a cell is placed in each type of
solution and whether the cell will shrink, expand and possibly lyse (burst) or remain unchanged.
Know that since there is always random motion of molecules that in an isotonic solution water is
moving in both directions through the membrane equally with no net change in size.
Be able to explain what passive transport means and know that osmosis and diffusion are
passive transport. Be able to explain that the limitation of passive transport is that it can only
transport molecules from areas of high concentration to areas of low concentration.
Be able to contrast passive transport (osmosis and diffusion) with active transport.
Be able to define endocytosis and exocytosis. Be able to give an example of a situation where
each of these processes would occur.
Be able to define equilibrium and know the difference between a dynamic and a static
equilibrium. Know which kind of equilibrium occurs for a cell in an isotonic solution.