Question

A cell membrane is a thin layer enveloping a cell. The thickness of the membrane is much less than the size of the cell. In a static situation, the membrane has a charge distribution of −2.5×10⁻⁶ C/m² on its inner surface and +2.5×10⁻⁶ C/m² on its outer surface. Draw a diagram of the cell and the surrounding cell membrane. Include on this diagram the charge distribution and the corresponding electric field. Is there any electric field inside the cell? Is there any electric field outside the cell?

a) Yes, there is an electric field inside the cell and outside the cell.
b) No, there is no electric field inside the cell but outside the cell.
c) Yes, there is an electric field inside the cell but not outside the cell.
d) No, there is no electric field inside or outside the cell.

Answer 1

The cell membrane has a charge separation that creates an electric field within its thickness, but there is no electric field inside the cell or outside the cell. The correct answer is option b) No, there is no electric field inside the cell but outside the cell.

Step-by-step explanation:

A cell membrane is a phospholipid layer that separates the interior of a cell from its external environment. It allows selective ion passage and plays a crucial role in maintaining the cell's electric potential. In a static situation, the membrane carries charge distributions of -2.5×10-6 C/m2 on the inner surface and +2.5×10-6 C/m2 on the outer surface. This separation of charge generates an electric field within the membrane itself. According to the principles of electrostatics, there would be no net electric field inside the cell (where the charges effectively cancel each other out) or outside the cell (the field lines start on positive charges and end on negative charges within the membrane). Thus, there are electric fields within the membrane but no electric field exists inside or outside the cell.

Given the thickness of the cell membrane (approx. 7 to 10 nm) and the potential difference across it (70 to 90 mV), the resulting electric field across the membrane can be significant. If the exterior of a neuron is at 0 V and the interior has a resting potential of about -90 mV, the electric field (E = V/d) across the membrane is immense, potentially on the order of 11 MV/m, which is fundamental to its function.

To answer the question presented, the correct option is: b) No, there is no electric field inside the cell but outside the cell.