Here's why:
* Ribosomes are the protein synthesis factories of the cell. They read the genetic code carried by messenger RNA (mRNA) and use that information to assemble amino acids into proteins. Proteins are the building blocks of many cellular structures and perform a wide variety of functions.
* DNA replication is the process of copying DNA, and it occurs in the nucleus. While this is essential for cell division and therefore reproduction of the cell itself, it's not the direct creation of new molecules within the cell in the way that protein synthesis is.
* Mitochondria are responsible for generating energy (ATP) for the cell, but they don't directly synthesize new molecules.
* Golgi apparatus processes and packages proteins, but it doesn't create them from scratch.
In summary: Ribosomes are the primary sites of protein synthesis, making them directly responsible for the reproduction of new molecules within the cell.
