Here's why:

* Mitosis is for growth and repair: Mitosis is a cell division process that creates two daughter cells that are genetically identical to the parent cell.

* Ploidy refers to chromosome sets: Ploidy describes the number of sets of chromosomes a cell has. For example, humans are diploid (2n), meaning they have two sets of chromosomes.

* Mitosis maintains ploidy: During mitosis, the chromosomes are duplicated, and then the cell divides, ensuring each daughter cell receives a complete set of chromosomes. Therefore, the ploidy stays the same.

Example:

* A diploid (2n) cell enters mitosis.

* The chromosomes are duplicated, resulting in 4n.

* The cell divides into two cells.

* Each daughter cell receives a full set of chromosomes, resulting in 2n for each daughter cell.

In conclusion: Mitosis maintains the ploidy of the parent cell, ensuring that each daughter cell has the same number of chromosome sets as the original cell.