Here's why:

* Ribosomes are essential for protein synthesis. They read the genetic code carried by messenger RNA (mRNA) and use it to assemble amino acids into proteins.

* Ribosomes are composed of two subunits: a large subunit and a small subunit. Both subunits are made up of ribosomal RNA (rRNA) and proteins.

* The nucleolus is a specialized region within the nucleus. It's the site of rRNA synthesis and the assembly of ribosomal subunits.

So, the nucleolus is responsible for producing the rRNA that forms the backbone of ribosomes, making it crucial for protein synthesis in the cell.