Given an extracellular [Pi-2] of 4mM and an intracellular [Pi-2] of 40 mM, what is the equilibrium potential of a plasma membrane permeable only to Pi-²?
Given an extracellular [Pi-2] of 4mM and an intracellular [Pi-2] of 40 mM, what is the equilibrium potential of a plasma membrane permeable only to Pi-²?
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
Section: Chapter Questions
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![### Understanding Equilibrium Potential of a Plasma Membrane
**Problem Statement:**
Given an extracellular \([Pi^{-2}]\) of 4mM and an intracellular \([Pi^{-2}]\) of 40 mM, what is the equilibrium potential of a plasma membrane permeable only to \(Pi^{-2}\)?
(Hint— you do *not* need a calculator to solve this question.)
**Answer Options:**
- +305 mV
- -61 mV
- +61 mV
- +30.5 mV
- 0 mV
- -30.5 mV
#### Explanation:
To understand this problem, let's break down the concepts required to find the equilibrium potential.
The equilibrium potential for an ion across a plasma membrane can be determined using the Nernst equation. However, with the hint indicating that a calculator is not needed, this implies that the answer can be derived by logical comparison or an understanding of typical values.
Given:
- **Extracellular \(Pi^{-2}\)**: 4 mM
- **Intracellular \(Pi^{-2}\)**: 40 mM
By noting that intracellular concentration is 10 times higher than the extracellular concentration (*40 mM / 4 mM = 10*), we know from standard chemistry that a tenfold concentration difference typically corresponds to an equilibrium potential shift of around -60 mV, due to the logarithmic nature of the Nernst equation.
Additionally, because the ion in question has a charge of -2, the equilibrium potential will be more negative compared to a monovalent ion. Hence, it will move towards a more negative value consistent with established electrochemical principles.
Among the given options, the most appropriate and equivalent estimate of the equilibrium potential would thus be **-30.5 mV** due to the increased complexity of divalent ions compared to the standard -60 mV seen in monovalent contexts.
Therefore, the correct option is:
- **-30.5 mV**](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fbd446b52-8c58-4d2e-95c3-f01363988023%2F9308005c-a671-48de-b4b4-65ad33376fe7%2Fnjzb1f_processed.jpeg&w=3840&q=75)
Transcribed Image Text:### Understanding Equilibrium Potential of a Plasma Membrane
**Problem Statement:**
Given an extracellular \([Pi^{-2}]\) of 4mM and an intracellular \([Pi^{-2}]\) of 40 mM, what is the equilibrium potential of a plasma membrane permeable only to \(Pi^{-2}\)?
(Hint— you do *not* need a calculator to solve this question.)
**Answer Options:**
- +305 mV
- -61 mV
- +61 mV
- +30.5 mV
- 0 mV
- -30.5 mV
#### Explanation:
To understand this problem, let's break down the concepts required to find the equilibrium potential.
The equilibrium potential for an ion across a plasma membrane can be determined using the Nernst equation. However, with the hint indicating that a calculator is not needed, this implies that the answer can be derived by logical comparison or an understanding of typical values.
Given:
- **Extracellular \(Pi^{-2}\)**: 4 mM
- **Intracellular \(Pi^{-2}\)**: 40 mM
By noting that intracellular concentration is 10 times higher than the extracellular concentration (*40 mM / 4 mM = 10*), we know from standard chemistry that a tenfold concentration difference typically corresponds to an equilibrium potential shift of around -60 mV, due to the logarithmic nature of the Nernst equation.
Additionally, because the ion in question has a charge of -2, the equilibrium potential will be more negative compared to a monovalent ion. Hence, it will move towards a more negative value consistent with established electrochemical principles.
Among the given options, the most appropriate and equivalent estimate of the equilibrium potential would thus be **-30.5 mV** due to the increased complexity of divalent ions compared to the standard -60 mV seen in monovalent contexts.
Therefore, the correct option is:
- **-30.5 mV**
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