What is the organelle that is not found in a mature red blood cell and suggest one disadvantage of this for the cell

the mitochondria is missing in a mature RBC. They lose their mitochondria during the third phase of the developmental pathway, a disadvantage of this is because they do not have many organelles left in the blood cell, their life span is limited.

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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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the denominator has a very specific role.