Ribosomes

Ribosomes are not organelles. They are not membrane-enclosed, instead they are macromolecules made of both RNA and proteins. If you ever have trouble remembering, just recall that there are ribosomes found in bacteria even though bacteria do not contain organelles. 

Moreover, not all ribosomes are located at the ER in eukaryotes (remember there is no ER in bacteria). Many of the ribosomes are free-floating in the cytoplasm. The ribosomes that are at the ER are only there temporarily. They are not technically part of the