The degree to which a cell membrane allows substances, especially ions, to pass through is called what?

• A. Conductance
• B. Excitability
• C. Capacitance
• D. Permeability

Answer: (D)

Permeability refers to how readily the membrane allows substances, especially ions, to cross it. This property depends on the presence and activity of ion channels and transporters; when permeability to a given ion is higher, that ion can move more easily across the membrane in response to its electrochemical gradient, which helps shape the resting membrane potential and responses like action potentials. In electrophysiology, the relative permeabilities of different ions (for example, potassium vs sodium) determine the membrane potential, as captured in models like the Goldman equation. Conductance is related because it describes the ease of current flow for a given voltage, but the fundamental property asked about here is permeability. Capacitance is about storing electric charge across the membrane, and excitability is the ability to respond to stimuli, not the passive passage of substances.