Ribosomal RNA or R-RNA. They are not membrane bound organelles and can be found in prokaryotes as well as eukaryotes.
Actually, ribosomes are made of rRNA and proteins, 60% of rRNA and 40% of proteins. The function of rRNA is mainly bind to sequences of mRNA and catalyse the peptide bond formation.
Ribosomes are not true organelles…they are much more like a RNP complex (RNA + Protein) that has the ability to sinthesyze polypeptide chains (proteins). Every living being needs ribosomes so they can express their genectic material.