A concentration of nerve cells in one area is called ?

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neuron

Explanation:

In the peripheral nervous system a bundle of axons is called a nerve. In the central nervous system a bundle of axons is called a tract.

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an organism's phenotype is the  form of a trait  that it  displays. for  flowercolor, a pea  plant  can  display  a phenotype of purple or white flowers. an organism's  genotype  is the alleles of a gene it contains. based on his data, mendel concluded that a phenotype can be  determined  by more than one  genotype.