What is the main purpose of scientific models?
a. the main purpose of models is to have a physical object to which to refer.
b. the main purpose of models is to represent observations.
c. the main purpose of models is to study systems that no longer exist.
d. the main purpose of models is to gain a better understanding of the world.

b. The main purpose of models is to represent observations.

Explanation:

Since we are talking about scientific models, we are talking as well about implementing the scientific method, which is based on observations. Scientists record their observations, plan and conduct experiments based on that and then collect data. It is once they have acquired the data that scientists may recurr to the usage of models in order to constitute ideas, processes or systems to describe and explain phenomena, using scientific models to represent observations.

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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