Cell growth actually occurs primarily during interphase, the period before mitosis begins.

Here's why:

* Mitosis is the process of cell division, focusing on splitting the existing cell into two daughter cells. It's about dividing the chromosomes and cytoplasm, not growing.

* Interphase is the stage where the cell does most of its growing, synthesizing new proteins and organelles, and doubling its DNA in preparation for mitosis.

To summarize: While mitosis is essential for life, it's the preparatory stage of interphase that's responsible for the actual growth of the cell.