Tetrodotoxin is a potent poison, produced by some newts, pufferfish, and blue-ringed octopus that affects sodium transport involved with the voltage gates in neurons. A friend swimming in the Caribbean is pricked by a pufferfish and gets very sick. The most likely action the poison takes is

Question

A.  Mimicking a symporter and allowing sodium to rush out and potassium to rush in.
B.  Mimicking an antiporter and allowing sodium to rush out.
C.  Blocking an antiporter so sodium cannot rush in.
D.  Blocking a symporter and keeping sodium from rushing in.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content
· What do you know about the effects of tetrodotoxin on ion movement in neurons? What other information is related to the question?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

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?

Answer 1

C.  Blocking an antiporter so sodium cannot rush in.


Clarify Question
· What is the key concept addressed by the question?
        o The question asks about the effects of tetrodotoxin on ion movement in neurons.
· What type of thinking is required?
        o You are being asked to evaluate statements about the effects of tetrodotoxin on ion movement in neurons.

Gather Content
· What do you know about the effects of tetrodotoxin on ion movement in neurons? What other information is related to the question?
        o When a neuron fires, sodium ions enter the neuron and potassium ions leave the neuron.  Both move in opposite direction through an antiporter. Tetrodotoxin blocks sodium entry into the neuron causing paralysis.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Because tetrodotoxin blocks sodium from entering the cell it is acting on an antiporter. If it mimicked a symporter or antiporter then it would stimulate sodium ion transport.  If sodium and potassium both entered a cell then the transporter would by a symporter.

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 This question asked you to evaluate statements about the effects of tetrodotoxin on ion movement in neurons. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you think that sodium and potassium both entered the cell through a symporter? Did you think that tetrodotoxin stimulated sodium ion transport?