During mitosis, the cell undergoes a series of changes in shape and structure in order to divide into two new cells. One of the most noticeable changes is the elongation of the cell. This elongation is caused by the growth of the spindle apparatus, which is a microtubule-based structure that helps to segregate the chromosomes. The spindle apparatus grows in length between the two poles of the cell, pushing the chromosomes apart and causing the cell to elongate.