Brainlies ! : ) why does water need a protein channel to move across the cell membrane?

The process is called Facilitated diffusion. It does not require ATP but does require cell membrane proteins which are called carrier proteins to carry the molecules across the cell membrane from an area of higher concentration to an area of lower concentration.

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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