Ribosomes

Ribosomes are small structures found in all living cells. They can be free in the cytoplasm or attached to Endoplasmic Reticulum (E.R), making Rough E.R. They can differ in size and number, according to whether they are found in Bacteria, Archaea or in Eukaryotes. There are a large number of ribosomes in cells. In Eukaryotes, there can be millions in one cell alone. As ribosomes are so small, (it has a diameter of 25-30nm approximately), an Electron Microscope is needed to see it.
Ribosomes are made up of two subunits, one larger than the other. The two subunits join together when attached to mRNA to make a protein in Protein Synthesis.
Ribosomes are also found in Mitochondria and Chloroplasts and carry out Protein Synthesis, specifically for these organelles.