The Nernst Potential is important to understanding how electrostatic charges dis

Question

The Nernst Potential is important to understanding how electrostatic charges distribute in cells and tissue. One example we have studied is a model cell with a high 10mM concentration of NaCl on the outside and a small 40M concentration of NaCl on the inside of the cell. Being a model, it is very simple and only contains Na channels. A physics student claims that the Nernst potential of Cl in this case would not be defined since there is no membrane channel present for Cl. A biology student on the other hand says that the Nernst potential is defined for any concentration difference, whether or not a channel is present. Discuss both viewpoints and suggest why each approach might be relevant in different contexts. Note: This is an essay question. Your answer will be judged not solely on its correctness, but for its depth, coherence, and clarity.

Explanation / Answer

The Nernst Equation enables the determination of cell potential under non-standard conditions. It makes use of ionic inflow and outflow to calculate the cell potential. From the view point of biology student, he is correct, because the Nernst potential is defined for any concentration difference. So, without concentration difference there would be no development of membrane potential. Here, the Cl ion concentration outside the cell is more compared to the cell inside. So, according to the equation, there should be a potential difference.

From the view point of physics student, he is also correct, because membrane potential occurs when there is an inflow and outflow of ions in different concentrations. Such flow is not present due to the absence of Cl membrane channels.

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