Is base 1 a purine or a pyrimidine, and how can you tell? Pyrimidine, because it has one ring structure.
Purine, because it has one ring structure.
Purine, because it has two ring structures.
Pyrimidine, because it has two ring structures.

Each DNA strand has a 'backbone' that is made up of a sugar-phosphate chain. Attached to each one of these sugars is a nitrogenous base that is composed of carbon and nitrogen rings. The number of rings this base has determines whether the base is a purine two rings or a pyrimidine one ring

Explanation: it really simple

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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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