Which diagram correctly illustrates the distribution of ions in a resting neuron? (Note: A larger symbol indicates a higher concentration of that ion.)

Question

A.  A

B.  B

C.  C

D.  D



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 ions in cells? 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?

 

Answer 1

B.  B

Clarify Question
· What is the key concept addressed by the question?
        o The question is asking about the relative distribution of key ions (sodium, potassium, and chloride) across the membrane of a neuron.
· What type of thinking is required?
        o This question is an analyze question because you have to understand the differential distribution (shown by the size of the icons) of ions in a neuron during its resting state.

Gather Content/Choose Answer
· What do you already know about ions in cells? What other information is related to the question?
        o To solve this problem, you’ll need to apply your knowledge of the differential concentration of ions across all cell membranes, which causes a membrane potential. At rest this potential is referred to as the resting membrane potential, as opposed to an action potential, which is caused by a rapid, but transient, shift away from the resting membrane potential. Resting membrane potential is largely controlled by the distribution of K+ ions, with equilibrium being reached with much greater K+ inside the cell compared to outside the cell. Action potentials are produced by an influx of Na+ ions going down their concentration gradient. Thus, the concentration of Na+ must be greater outside the cell than inside. Remember that this unequal distribution of Na+ and K+ is produced by sodium-potassium pumps that transport 2 potassium ions inside and 3 sodium ions outside of the cell.

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, great! If not, where in your thought process did things go wrong? If you arrived at an incorrect answer, were you thinking that a neuron at rest should have its ions in equilibrium and did you wrongly assume that electrochemical equilibrium meant that concentrations of ions are the same on both sides of the membrane?
        o Answering this question correctly depended upon on distinguishing between the differing distribution patterns of Na+, K+, and Cl- ions while at resting membrane potential.