Review for the third hour exam, part four Some of these may be similar to questions previously posted. 87) What is polyspermy? Why have methods evolved to prevent polyspermy? What are the differences between fast blocks and slow blocks to polyspermy? Suggest how blocks to polyspermy be used for contraception i.e. to prevent fertilization? (hint by activating any of the blocks before fusion with sperm; or by inhibiting the activation of any of the blocks to polyspermy, even after fusion with sperm. 88) What function is served by the thousands of cortical vesicles that are located just inside the plasma membrane of oocytes? Why do the membranes of these vesicles fuse with the plasma membranes of oocytes? 89) Why do unfertilized frog oocytes not rotate so that their heavier vegetal pole side is oriented downward, and their darkly pigmented side is oriented upward? How can you tell whether frog eggs have been fertilized yet, just by looking at them, even at distances of 10 or 20 feet. 90) What are similarities between action potentials of nerve fibers and the fast block to polyspermy? 91) Why would all the blocks to polyspermy be stimulated by putting oocytes in water containing high concentrations of potassium ions? What would be the effect of sea water (i.e. high concentrations of sodium chloride? What about calcium chloride? What if you injected potassium chloride solutions into oocytes? Into nerve or muscle cells? 92) Describe the changes in cytoplasmic concentrations of calcium ions that occur soon after fertilization. How are these changes made visible using proteins or other chemicals that become more fluorescent in response to increased concentrations of calcium ions? 93) Which differentiated cell types have resting potentials? Which have higher concentrations in their cytoplasm than in whatever extracellular fluids around them? 94) What percentage of their ATP do cells use to pump sodium ions out of their cytoplasm? 95) What functions are already known to be served by the voltage differences between the inside versus the outside of cells? **96) What functions of this voltage difference have not been discovered yet? Suggest some possible functions? Suggest experiments to test whether any given function is or is not served by those transmembrane voltage differences. 97) Explain how or whether positive potassium ions are able to cause the cytoplasm to have a more negative voltage than the outside, even though potassium ions have positive charges. 98) As a rule, are living cells more permeable to potassium ions or to sodium ions? Would the resting potential (potential = voltage) of a cell continue to exist in a cell that was not permeable to any ions, neither potassium, sodium, chloride, or calcium? (Hint: no, it wouldn't). How would the membrane voltage be affected if the membrane became equally permeable to both sodium and potassium ions? *99) Suggest how (or whether) bone formation might be stimulated, or otherwise controlled by changes in ion permeability. (To which ions?) 100) If the fast block to polyspermy were 100% effective, would there be any need for the slow blocks to polyspermy? What if the depolarization produced by fertilization lasted only for a few minutes, but the slow blocks were permanent? What if sperm were very rare? So rare that an oocyte would only come into contact with a sperm once or twice an hour: would that affect the need for the fast block to polyspermy? (Hint: Yes, I would think so.) 101) What is the advantage of electrical depolarization as a means or sending biological messages, as compared with secretion and diffusion of stimulatory or inhibitory substances? What is a DISadvantage? *102) Could electric depolarization be part of the mechanism by which notochord mesoderm induces ectoderm to become neural tube rather than somatic ectoderm? *Suggest one or more experiments by which that possibility could be tested? **103) If voltage changes were part of the mechanism of embryonic induction, how would this probably been first discovered? **104) Could differences in voltages be a practical method for controlling which parts of a developing embryo become mesoderm, which parts become ectoderm, which parts become neural ectoderm, etc.? Suggest experiments to test such possibilities. **105) Would you expect cancer cells to have abnormal resting potentials? **106) Could contact inhibition of cell locomotion be stimulated by inducing depolarization of resting potentials? **107) How might high voltage power lines affect membrane voltages, as was a source of much worry 15 or 20 years ago, until people got bored with that controversy, despite never having disproved it. "What about the voltage fields produced by cell phones?" [Is that a reason not to get one?] Design experiments to test such possibilities? *108) Could membrane potentials be produced by differences in permeabilities to chloride versus some other negative ion? *Or can only positive ions produce such effects? Or do you need two different ions of the same charge (like sodium and potassium)? * What if cells were much more permeable to chloride ion than to any other ions? *109) What if the osmotic pressure of cells in certain plants changed in response to voltage difference across cell membranes? What phenomena could that explain? **110) Can you figure out how Venus Fly Traps work? **111) What about "Electric Eels? Do you know how they create such large voltages (hint, using a special kind of cell that evolved from muscle cells? (Some other electric fish use modified nerve cells, instead of modified muscle cells; none use modified oocytes.) Hint: what if you had a pile of muscle cells, all of whose sodium channels were concentrated in the membranes on the tops of the cells, with few or none on the bottoms (or vice versa). **112) If you squeezed an eel, and it shocked you, would people say the cause must be piezoelectricity? *113) Suggest possible explanations for the fact that macrophages (and osteocytes) crawl preferentially toward positive electrodes, but all other differentiated cell types either crawl toward negative electrodes (as epidermal cells do) or line up perpendicular to electric fields (as mesenchymal cells and muscle sells do)? *114) Could atherosclerosis be related to changes or abnormalities in membrane voltages? Explain how that might occur. Remember that atherosclerotic "plaque" a) Is IN the wall of arteries,among the smooth muscle cells, b) NOT stuck to the inside wall of the wall, inside the endothelial cells. c) Largely made of what were macrophages d) That actively crawled there e) And also made of disorganized and no-longer parallel circumferential smooth muscle cells! *115) If a tissue culture cell is put in a voltage gradient, which end or side of that cell will be depolarized and which will be hyper-polarized? *116) What if you put an oocyte in a voltage gradient? Would parts of the oocyte secrete their cortical granules, whether or not fertilization had occurred. Would other parts of an oocyte surface NOT secrete its cortical granules, even after fertilization has occurred? *117) Again, referring to the situation of an oocyte in an electric voltage gradients, would some parts of its surface be made more likely to fuse with sperm? Which parts? **118) Why do you suppose there isn't more research on such subjects (any more)?