Ribosomes are synthesized by the:

Ribosomes are synthesized in the nucleolus, which is a dense, membrane-less structure located within the nucleus of eukaryotic cells. The nucleolus is primarily responsible for the production and assembly of ribosomal RNA (rRNA) and the initial stages of ribosome assembly. It combines rRNA, which is transcribed from ribosomal DNA (rDNA), with ribosomal proteins imported from the cytoplasm to form ribosomal subunits. Once synthesized, these subunits are then transported out of the nucleolus and into the cytoplasm, where they combine to form functional ribosomes that play a crucial role in protein synthesis.

In contrast, the endoplasmic reticulum is involved in the synthesis of proteins and lipids and is not directly responsible for ribosome production. Mitochondria have their own ribosomes but do not synthesize ribosomes for the cell's cytoplasm. The Golgi apparatus is crucial for modifying, packaging, and distributing proteins and lipids synthesized in the endoplasmic reticulum, but it does not produce ribosomes. Therefore, the identification of the nucleolus as the site of ribosome synthesis is key to understanding the cellular mechanisms involved in protein production.