Many researchers think that the first eukaryotic cells obtained energy for life-sustaining functions from organic compounds. Given this information, which of the following organelles most likely appeared last in eukaryotic cells?a. plasma membrane b. chloroplast c. ribosome d. nucleus

Chloroplast

Explanation:

The chloroplast is an organelle capable of synthesizing energy from solar radiation by a mechanism referred to as photosynthesis. The origin of this organelle likely can be traced back to an endosymbiotic event where a bacterium was engulfed by a primitive (ancestral) eukaryotic cell

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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