Here's why:

* Ribosomes are essential for protein synthesis. They read the genetic code from messenger RNA (mRNA) and use it to link amino acids together to create proteins.

* The nucleolus is a dense region within the nucleus of eukaryotic cells. It's not membrane-bound, but rather a collection of proteins and RNA molecules.

* The nucleolus is the site of ribosomal RNA (rRNA) synthesis and the assembly of ribosomes.

Let me know if you have any other questions about organelles or cell biology!