Study Guide 8
Last revised: Friday, February 15, 2002
Topic: Membranes
Chapter 8.

Note: The properties of membranes are largely dynamic -- things move across membranes. It is difficult to appreciate this dynamic aspect from the study of still diagrams. I strongly recommend that you spend some time with the Biology Place activity on Biomembranes, which involves many animations and interactive graphics.

  1. What molecules compose cell membranes, and in approximately what approximate %?
  2. What types of functions do membrane proteins carry out? What function(s) do membrane lipids serve?
  3. What is the fluid mosaic model?
  4. Which of the following molecules could travel across a plasma membrane without a protein carrier? water, glucose, oil, hemoglobin, sodium ion, messenger RNA, ethanol.
  5. Which of the molecules listed in the previous question would require a specific carrier in order to be transported into a cell? Is there anything on the list that you would not expect to see transported across a membrane under any circumstances? If so, what?
  6. Explain what is meant by the terms “isotonic”, “hypertonic”, “hypotonic”, “lysis”, “plasmolysis”, “shrinkage” and “osmosis”. What is the equivalent salt concentration of a human cell?
  7. A wilted lettuce leaf is placed in fresh water. What happens? Which of the terms mentioned above are involved?
  8. A cook pickles some tomatoes in concentrated brine. Fungi and bacteria (cells with walls) can no longer grow. Explain. Which of the terms mentioned above are involved?
  9. How does “facilitated diffusion” differ from “passive diffusion”? How does “facilitated diffusion” differ from active transport? Which of these processes would be affected by a drug that binds tightly to proteins and blocks their activity?
  10. Ion gradients are vitally important to cells. With respect to human cells, which of the following ions are normally kept at very different concentrations across cell membranes: Ca++, Na+, K+, Cl-? Which ions are in higher concentration outside the cell? Inside the cell?
  11. What is the difference between symport, antiport, and ATP pumps? What is the immediate source of energy for each process?
  12. (a) Identify each of the following terms: phagocytosis, pinocytosis, receptor-mediated endocytosis, and exocytosis. Give an example of a situation in which each would occur.
    (b) Explain the process by which iron gets from the bloodstream into human cells. Compare this with the uptake of glucose.
  13. What function is served by gap junctions? Desmosomes? Tight junctions? Plasmodesmata? Which of these are found in animals? Plants? (Note: these topics were treated in Chapter 7, but the study guide for Chapter 7 did not ask about them).


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