A Hawaiian legend tells of a village that angered a shark god. In revenge, a "seaweed" began to grow in the tidepools that killed anyone who touched it. In fact, this "limu-make-o-Hana" -- a zoanthid cnidarian -- contains a palytoxin that locks the sodium-potassium pump open, allowing free flow of ions. If a villager suffers palytoxin poisoning, which way will the ions in his neurons flow?
Palytoxin is incredibly toxic, perhaps the second most dangerous non-peptide toxin. It targets the sodium-potassium pump, locking it open and forming a channel through which the ions can passively flow. Palytoxin is produced by zoanthid cnidarians (soft coral), and there have been incidents of poisoning from zoanthids within marine aquaria tanks in people's homes. It is also thought to be the source of the legend of the Limu make o hana ("Seaweed of Death from Hana").
A. all ions will flow out
B. potassium in, sodium out
C. chloride and sodium out, potassium in
D. sodium in, potassium out
Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
Gather Content/Choose Answer
· What do you already know about sodium and potassium? What other information is related to the question?
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
D. sodium in, potassium out
Clarify Question
· What is the key concept addressed by the question?
o Sodium and potassium ion flow.
· What type of thinking is required?
o This is an analyze question because you have to consider the normal distribution of ions across a cell membrane, and then predict the result of free movement of these ions.
Gather Content/Choose Answer
· What do you already know about sodium and potassium? What other information is related to the question?
o To solve this problem, you’ll need to understand that sodium normally has a greater concentration outside the cell and potassium has a greater concentration inside the cell. If a channel is locked open, this would allow free flow of sodium and potassium. Sodium will rush into the cell, and potassium will rush out of the cell, down their concentration gradients. This would reduce the ionic gradients and prevent the formation of action potentials leading to paralysis.
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
o If you figured out the correct answer, good job! If not, where did you go wrong? Did you remember that the distribution of sodium and potassium across the cell membrane are opposite of each other, and that sodium has a greater concentration outside of the cell, whereas potassium has a greater concentration inside the cell. Did you recall that ions always flow down their electrochemical gradients?
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