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Chapter 4: Problem 21

When a membrane potential is positive, there is an excess of cations over anions inside the cell. (true/false)

Short Answer

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Step by step solution

01

Define membrane potential

First, let's define membrane potential. Membrane potential refers to the difference in electric charge across a cell membrane. It is the result of the distribution of ions, such as cations (positive ions) and anions (negative ions), inside and outside of the cell.
02

Identify positive and negative potential

If the membrane potential is positive, this means that the inside of the cell is positively charged when compared to the outside. Likewise, a negative potential would mean the inside is negatively charged compared to the outside.
03

Analyze the ion distribution for positive potential

A positive membrane potential indicates an excess of positive charges inside the cell compared to the outside. This typically happens when there is an abundance of cations inside the cell or a relative lack of anions inside compared to outside.
04

Determine the truth value

Given that a positive membrane potential signifies more positive charges (cations) inside the cell than negative charges (anions), the statement that a positive membrane potential corresponds to an excess of cations over anions inside the cell is true.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Cations: The Positive Particles
Cations are ions that carry a positive electric charge. These ions arise when an atom or molecule loses one or more electrons, which have a negative charge, resulting in a net positive charge.
  • Common cations include sodium \((Na^+)\), potassium \((K^+)\), calcium \((Ca^{2+})\), and magnesium \((Mg^{2+})\).
  • Cations play a crucial role in many biological processes, such as muscle contraction and nerve impulse transmission.
In cells, cations are essential for creating and maintaining the membrane potential. They move through channels in the cell membrane, contributing to the electric charge difference between the interior and exterior of the cell.
Anions: The Negative Counterparts
Anions are the opposite of cations; they are ions that carry a negative electric charge. An anion is formed when an atom or molecule gains electrons, which adds negative charge to it.
  • Examples include chloride \((Cl^-)\), bicarbonate \((HCO_3^-)\), and phosphate \((PO_4^{3-})\).
  • Anions are vital in processes like balancing the charges in cells and maintaining electrical neutrality.
Anions in the cell balance the effects of cations to help stabilize the membrane potential. They are also involved in essential cellular processes, such as metabolism and regulating the cell's osmotic balance.
Electric Charge and Membrane Potential
Electric charge plays a central role in establishing the membrane potential. It is the property that explains the difference in electron count, resulting in positive and negative charges.
  • Inside cells, this separation of charges leads to a potential gradient across the cell membrane.
  • Cell membranes have selective ion channels that allow specific ions to pass through, contributing to the potential gradient.
The membrane potential is influenced by the electric charge of ions and the permeability of the cell membrane. When a membrane is more permeable to cations, it can lead to a positive membrane potential if the positives outweigh the negatives inside the cell.
Ion Distribution in Cells
Ion distribution refers to how ions are arranged inside and outside of the cell. This distribution is crucial for the membrane potential and cellular function.
  • Diffusion and active transport are primary mechanisms that manage ion distribution across cell membranes.
  • Ion pumps, like the sodium-potassium pump, actively transport ions against their concentration gradient to maintain proper distribution.
A positive membrane potential implies a higher concentration of cations inside the cell compared to anions. As cations and anions move, they work to equalize the concentration on both sides of the membrane, sustained by energy-consuming mechanisms, maintaining the cell's function and stability.

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Most popular questions from this chapter

For a substance crossing a cell membrane, the chemical driving force a) Depends only on the concentration gradient, regardless of whether the substance is an ion. b) Depends only on the concentration gradient if the substance is uncharged, but also depends on the electrical force if the substance is an ion. c) Is the total driving force on the substance, even if it is an ion. d) Is the force that pushes molecules across the membrane, but only if the substance is actively transported. e) Always favors movement of a molecule into the cell.

Given that the potassium equilibrium potential is \(-94 \mathrm{mV}\) and the sodium equilibrium potential is \(+60 \mathrm{mV}\), which of the following statements is true for forces acting on sodium and potassium when a cell is at \(-70 \mathrm{mV}\) ? a) The electrochemical gradient for \(\mathrm{Na}^{+}\) tries to move it into the cell b) The electrochemical gradient for \(\mathrm{K}^{+}\) tries to move it into the cell c) Both a and b are correct. d) Neither a nor b is correct.

Which of the following is located in greater concentration inside cells compared to outside? a) Potassium ions b) Sodium ions c) Proteins d) Potassium and sodium ions are both located in greater concentration inside cells. e) Potassium ions and proteins are both located in greater concentration inside cells.

Movement of \(\mathrm{Na}^{+}\)in sodium-linked glucose transport, in sodium- proton exchange, and via the sodium-potassium pump are all examples of a) Primary active transport. b) Passive transport. c) Mediated transport. d) Simple diffusion.

Assuming that \(E_{\mathrm{Na}}=+60 \mathrm{mV}\), \(E_{\mathrm{C}}=-90 \mathrm{mV}\), and \(V_{\mathrm{m}}=-70 \mathrm{mV}\), find the direction of the electrochemi- cal driving forces acting on \(\mathrm{Na}^{+}\)and \(\mathrm{Cl}^{-}\) ions. In which direction will the ions move if they are transported passively? If they are transported actively? (Extra chal- lenge: From the sign of \(E_{\mathrm{C}}\), determine the direction of the concentration gradient of \(\mathrm{Cl}^{-}\)ions.)
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