Question

When a membrane is at the resting potential, the concentration of:
A) Sodium and potassium ions are higher on the inside of its membrane.
B) Sodium and potassium ions are higher on the outside of its membrane.
C) Sodium ions are higher on the inside of its membrane and potassium ions are higher on the outside.
D) Sodium ions are higher on the outside of its membrane and potassium ions are higher on the inside.

Answer 1

Hint:
All cells have an electrical potential difference across their plasma membrane. Membrane potential is established due to differences in ion concentration across the membrane and the selective movement of ions along the electrochemical gradient through ion-specific channels present in the membrane.

Complete step by step answer:
Excitable cells can change their membrane potential when exited. The constant membrane potential in the non-excitable cells and those of excitable cells when they are at rest is called resting membrane potential.
In animal cells, the resting potential is dictated predominantly by the K⁺ ions gradient. The predominant positive ion inside the cell is the K⁺ ions. The high intracellular concentration of K⁺ ions is, in part, generated by the Na⁺-K⁺ pump, which actively pumps K⁺ into the cell. This leads to a large concentration difference of K⁺ and Na⁺ ions across the plasma membrane, with the concentration of K⁺ ions being much higher inside the cell than outside and the concentration of Na⁺ ions higher outside the cell.

Option ‘D’ is correct

Note:
The plasma membrane, however also contains a large number of K+ leaky channels. These open channels allow potassium ions to move freely. Transfer of positive charge to the exterior leaves behind an unbalanced negative charge within the cell, thereby creating resting potential.