According to the source “British Society for Cell Biology” (n.d.), “ribosomes help to produce proteins. Ribosomes are found in prokaryotic (bacteria)  and eukaryotic cells Those found in prokaryotes are usually smaller than those found in eukaryotes because bacterial and archaeal cells are about 10 times smaller than eukaryotic cells (Cowan, 2017). Ribosomes in mitochondria and chloroplasts are similar in size to those in bacteria.  There are about 10 billion protein molecules in a mammalian cell and they are produced by ribosomes. A quickly growing mammalian cell can carry approximately 10 million ribosomes., for example, a single cell of E. Coli can hold approximately 20,000 ribosomes, and this explains about 25% of the total cell mass.”