Nitrogen gas is more abundant in our atmosphere than oxygen! However, nitrogen needs to be converted into different forms to be used by many organisms. Bacteria are highly involved in this! Describe the role of (A) bacteria fixing nitrogen as they live symbiotically with some plant species, (B) nitrifying bacteria, and (C) denitrifying bacteriain the nitrogen cycle

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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thinking it would be d not too sure but i think it's right

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.