Under resting conditions, the cell membrane remains impermeable to all ions except_____________?
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Answer: B. K+
Explanation
At rest, the plasma membrane is selectively permeable mostly to potassium ions. Potassium leak channels allow potassium ions to cross the resting membrane freely. Resting membrane potential depends heavily on this selective potassium permeability. Ion gradients across cell membranes are maintained by active transport pumps. Sodium-potassium pumps work constantly to establish resting ionic concentrations. Membrane permeability changes rapidly during action potential propagation.
Neurobiologists study resting membrane potentials to understand nerve signal transmission. Cardiac muscle cells rely on regulated ion permeability for rhythmic contractions. Pharmacological agents can block specific ion channels to alter cell excitability. Sodium ions remain largely excluded from crossing the resting cell membrane. Chloride ions do not have high permeability during resting membrane conditions. Phosphate ions are trapped inside cells and cannot cross freely at rest.
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