Final answer:
The statement is true; in the absence of active chloride transport, the chloride ion concentration across a neuron's plasma membrane is determined by the membrane potential, due to the electrochemical gradient.
Step-by-step explanation:
In the context of a neuron's plasma membrane, the statement that membrane potential will determine the concentration of chloride ions across the membrane in the absence of active transport is true. The cell membrane of a neuron in its resting state is selectively permeable, allowing certain ions to diffuse naturally down their concentration gradient. Potassium (K+) and chloride (Cl-) ions can migrate through the membrane, while sodium (Na+) typically cannot.
For chloride ions (Cl-), the electrochemical gradient, which is a combination of the concentration gradient and the electrical gradient (membrane potential), governs their movement. If active transport is not contributing to chloride ion movement, then this diffusion is primarily influenced by the membrane potential. A buildup of charge on either side of the membrane creates a voltage known as the resting membrane potential. This potential determines the movement of ions: Cl- will tend to move towards areas of opposite charge, balancing the chemical and electrical forces until equilibrium is reached.
Therefore, when active chloride transport is not occurring, the concentration of chloride ions across a neuron's plasma membrane will indeed be determined by the membrane potential.