Why might different cells of the same organism have cell cycles of different durations?

Cell cycles:

The amount of time or the duration of time required to complete the development and maturation of the body cells. As the parent cells are present less in number and then through the process of cell division the cells divides and forms more like itself.

Explanation:

Duration of the cell cycle:

From the initial point to the last by means of the maturation of a single, there is a sequence or chain of phases through which the cell passes and they develop into a more complex form. But, some phases requires more time then the rest of the phases.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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