Question

an action potential in a neuronal membrane differs from a graded potential in that
multiple choice
an action potential requires the opening of ca²⁺ channels, whereas a graded potential does not
an action potential is propagated without decrement, whereas a graded potential decrements with distance
an action potential has a threshold, whereas a graded potential is an all - or none phenomenon
movement of na⁺ and k⁺ across cell membranes mediate action potentials, while graded potentials do not involve movement of na⁺ and k⁺
action potentials vary in size with the size of a stimulus, while graded potentials do not.

Explanation:

Action potentials are all - or - none events that are propagated without decrement along the axon. Graded potentials are local changes in membrane potential that decrease in magnitude with distance from the source of stimulation. The other statements are incorrect: Action potentials don't always require $Ca^{2 +}$ channels opening (sodium channels are crucial for the up - stroke), graded potentials are not all - or - none, both action and graded potentials involve ion movements ($Na^+$ and $K^+$), and graded potentials vary in size with the size of the stimulus.

Answer:

B. an action potential is propagated without decrement, whereas a graded potential decrements with distance