Homework #3

  1. Sketch the I-V relationship for a positively charged ion using the constant field equation with [C]in/[C]out=0, 0.1,1,30, infinity.
  2. The paramecium has a resting potential (RP) and an action potential (AP) similar to many neural potentials. In typical pond water, the figure shows the AP and the RP for the cell. If one varies the extracellular potassium only or extracellular calcium, the results are shown in the lower part of the figure:

    Assume that it is normally only permeable to these two ions and water. Answer these:
    1. In the resting statem which is true:
      1. PK > PCa
      2. PK = PCa
      3. PK < PCa
    2. What about at the peak of the AP?
    3. Compared to the ionic concentrations pf pond water, is [K]in greater than, less than or equal to [K]out? Explain.
    4. Answer the same for calcium
    5. When the posterior end of the organism is mechanically tapped, the membrane transiently hyperpolarizes. What permeability changes might be responsible?