Ribosomes are 30sand 50s
What is meant by that
Prokaryotes have 70S ribosomes, each consisting of a small (30S) and a large (50S) subunit. Their small 30s subunit has a 16S RNA subunit (consisting of 1540 nucleotides) bound to 21 proteins. The large 50s subunit is composed of a 5S RNA subunit (120 nucleotides), a 23S RNA subunit (2900 nucleotides) and 31 proteins.
These subunits are basically different variations(like a classification) of ribosomes that make up the 70 s sub unit. Ribosomes are used to make protiens in the cells body.simply think that if you need to make a 70s ribosome you need 30s sub unit and 50s sub unit joined together.