PHOTOSYNTHESIS ESSAY 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 ejkaryotes

__ 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