CELL QUESTION 1993:					L. PETERSON/AP BIOLOGY
	Membranes are important structural features of cells.
	   (a) Describe how membrane structure is related to the transport 
	          of materials across a membrane.
	   (b) Describe the role of membranes in the synthesis of ATP in either
	          respiration or photosynthesis.


     Membranes serve diverse functions in eukaryotic and prokaryotic cells. One
     important role is to regulate the movement of materials into and out of cells.
     The phospholipid bilayer structure (fluid mosaic model) with specific membrane
     proteins accounts for the selective permeability of the membrane and passive
     and active transport mechanisms. In addition, membranes in prokaryotes and in
     the mitochondria and chloroplasts of eukaryotes facilitate the synthesis of ATP
     through chemiosmosis.
  
     PART A. (6 Maximum)
     Membrane Structure (3 Internal Maximum)
     __ Phospholipid structure - hydrophilic, hydrophobic, amphipathic
     __ Phospholipid bilayer / fluid mosaic description
     __ Proteins embedded in the membrane
     __ Sterols embedded in the membrane
     __ Well-labeled diagram may replace one of the above
  
     Membrane Transport (3 Internal Maximum)
     __ Use of the term "selectively permeable" or a good definition of
           selective permeability or an explanation of the role of phospholipids 
           or proteins including nuclear pore proteins in determining selective 
           permeability
     __ Description of the effect of size, charge, polarity, lipid solubility  on
           membrane permeability
  
     Mechanisms + description related to structure:
     __ Passive transport: diffusion / osmosis + reference to membrane gradient
     __ Ion channel: transport as a mechanism for a change in permeability
     __ Facilitated diffusion: description (symport, antiport, uniport)
     __ Active transport: description
     __ Exocytosis, endocytosis, phagocytosis, pinocytosis: description
  
     (1 pt additional) A good example of one of the above mechanisms
  
     PART B. Role of the Membrane in the Production of ATP in    Photosynthesis or
  Respiration (6 Maximum)
     Chemiosmosis:
     __ Involved molecules are embedded in the membrane
     __ Electron carriers are sequentially organized
     __ The energy comes from the flow of electrons
     __ H+ / Proton / pH gradient established
     __ Movement through the membrane generates ATP
     __ A specific protein makes ATP
  
 

 
  	RESPIRATION		or		PHOTOSYNTHESIS

  __ Site is the mitochondrion			__ Site is the chloroplast
  __ Inner mitochondrial membrane			__ Thylakoid / grana membranes
        (cristae) are involved in eukaryotes		      are involved in eukaryotes
  __ Folded membrane present			__ Folded membrane present
  __ Cell membrane is involved in			__ Thylakoid / grana membranes
       prokaryotes					      involved in prokaryotes
  __ Correct direction of H+ flow			__ Correct direction of H+ flow