The nucleolus is a dense region within the nucleus responsible for the synthesis and assembly of ribosomal RNA (rRNA) and the formation of ribosomes.
- Option (1) is incorrect: The mitochondria are involved in energy production through cellular respiration, not the synthesis of rRNA.
- Option (2) is correct: The nucleolus is the site of rRNA synthesis, which is then combined with proteins to form ribosomes.
- Option (3) is incorrect: The endoplasmic reticulum is involved in protein synthesis and lipid metabolism, but it does not synthesize rRNA.
- Option (4) is incorrect: The Golgi apparatus is responsible for modifying, sorting, and packaging proteins, not for synthesizing rRNA.
Thus, the nucleolus is responsible for the synthesis of rRNA in eukaryotic cells.