Which of the following genetic elements is transcribed into a single mrna? 1)the inducer 2) the promoter 3) the repressor 4) the structural genes 5) the operator

The genetic element which is transcribed into a single mRNA is THE STRUCTURAL GENES.

The lac operon is found in organisms such as E coli. The lactose (lac) operon is made up of genes, which brings about metabolism of lactose in E coli. The operon is expressed only when glucose is absent and lactose is available. The lac repressor and CAP (Catabolite Activator Protein) are the two regulators, which turn the lac operon on and off.  

Structurally, the lac operon is made up of three different genes, which are Lac Z, Lac Y and Lac A. These three genes are transcribed as a single messenger RNA (mRNA) under the control of a single promoter. These genes function by specifying proteins, which make the E coli cells to make use of lactose for energy. In addition to the three genes, the lac operon also contains regulatory DNA sequences such as the promoter region, operator region and the CAP binding site.  

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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clumped distribution, because you'de have all of the population gathered in a relatively small are.

it's the most common because it provides protection and a mate for reproduction

example: humans, seeweed, cattles, etc.