Concepts of Biology (BIOL115) - Dr. S.G. Saupe (; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

  Membrane Questions

 1. The cells of plant seeds store oil in the form of droplets enclosed by membranes. Unlike the cell membrane, the oil-droplet membrane probably consists of a single layer of phospholipids rather than a bilayer. Draw a model for a membrane around an oil droplet. Explain why this arrangement would be more stable than if it were a bilayer.

2. What is the importance of having sugars on the external side of the cell membrane? In other words, why are some membranes sugar-coated? Give one example of how these are used by an organism. What is the technical term for the sugar-coating?

3. Which of the following is TRUE?

    1. phospholipids only occur in some membranes
    2. certain proteins are unique to each membrane
    3. only some membranes are selectively permeable
    4. only some membranes are constructed from amphipathic molecules
    5. some membranes have the hydrophobic surface exposed to the cytoplasm while others have the hydrophilic surfaces facing the cytoplasm

4. According to the fluid mosaic model of protein structure, proteins of the membrane are:

  1. spread in a continuous layer over the inner and outer surfaces of the membrane
  2. confined to the hydrophobic core of the membrane
  3. embedded in a lipid bilayer

5. When a cell membrane is split by freeze-fracture into its outer and inner leaflets, the bumps seen in the electron micrographs are images of :

  1. integral proteins
  2. peripheral proteins
  3. phospholipids
  4. cholesterol molecules

6. Which of the following factors would increase membrane fluidity?

  1. greater proportion of unsaturated phospholipids
  2. a lower temperature
  3. a higher protein content in the membrane
  4. a greater proportion of large glycolipids compared to lipids having smaller molecular weights

7. Consider an artificial cell with a semi-permeable membrane that is permeable to simple sugars (glucose, fructose) but not disaccharides (sucrose). If the cell contains an aqueous solution of 0.03 M sucrose and 0.02 M glucose and is then immersed in a beaker containing water and 0.01 M sucrose, 0.01 M glucose and 0.01 M fructose then:

  1. which solute(s) will exhibit a net diffusion into the cell?
  2. which solute(s) will exhibit a net diffusion out of the cell?
  3. which solute(s) would be an example of dialysis?
  4. in which direction will there be a net osmotic movement of water?
  5. After the cell is placed in the beaker, it will: become more flaccid, become more turgid; or no change in pressure will result

8. If a cell is placed in a solution and it swells, the solution is probably:

  1. isotonic to the cell
  2. hypotonic to the cell
  3. hypertonic to the cell
  4. iso-osmotic to the cell
  5. hyper-osmotic to the cell
  6. hypo-osmotic to the cell


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