The first species to colonize a barren area is a Pioneer Species
The spindle fibers produced by the centrioles are necessary for the division of the chromosome at the time of the anaphase. In case, the centrioles do not perform their task, the genetic material in the cells may not divide equally due to the lack in the separation of the chromosomes. Hence, the problem with the centrioles may lead to the unequal division of the genetic material during the cell division process.
Hence, the correct answer is centrioles.
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Because it serves as protection for a vital organ in the body. Also if the skull could move it would make the brain very vulnerable.