u 2. (45 pts) It appears to be a metazoan having a nervous system but you cannot
ID: 3475999 • Letter: U
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u 2. (45 pts) It appears to be a metazoan having a nervous system but you cannot even be sure it is from Earth. Nothing like it has been described. But, of course it IS from our universe. It has big neurons and you can readily isolate them. You write a stunning manuscript to characterize your find (which you call Giganteae crudstufferi) only to have it returned with scathing reviews that require you to actually do some experiments to describe the neurons. Using borrowed equipment, you easily extract extracellular fluid and discover it has the following concentration of major ions (in mM). You have discovered a new life-form lurking in the back of your refrigerator. Na+ 680 K+ 8 CI- 950 Rb+ 300 There may be other ions around, but these are the majority. You cannot measure intracellular concentrations directly but you have begged use of Dr. J's electrophysiology rig, carefully dissect your precious critter and measure a membrane potential in a selected neuron that = +26.0 mV Present the one most plausible (given the circumstances) explanation of these observations in terms of ionic distributions and relative permeability (hypothesis). Then design and describe an experiment that you would conduct to test your ideas (prediction and experiment). Dr. J is out fishing and is not available for consultation. NOTE: You may make solutions to order and record intracellular voltages, but you do not have access to specialized equipment beyond what is necessary to do this. Use only one sheet for your answer. You may include graphs or diagrams as long as all fits on one sheet.Explanation / Answer
The membrane is permeable to K+, as the potential moves out but the the positive charge is dropped to +26 mV. The membrane is impermeable to Na, Cl, Rb giving a net positive charge to the membrane.
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