A cell makes a copy of its DNA before mitosis for a very important reason: to ensure that each daughter cell receives a complete and identical set of chromosomes.

Here's why:

* Mitosis is for growth and repair: Mitosis is the process by which a single cell divides into two identical daughter cells. This is essential for growth, development, and tissue repair.

* Chromosomes carry genetic information: Chromosomes are made up of DNA, which contains the genetic instructions for building and maintaining an organism.

* Each daughter cell needs a full set: If a cell divided without replicating its DNA, each daughter cell would only receive half the genetic information. This would be disastrous, as the cells would be unable to function properly.

In summary: DNA replication ensures that each new cell receives a complete set of genetic instructions, allowing for proper development and function.