Many ribosomes may associate with a single mRNA to form multiple copies of a polypeptide simultaneously. Such strings of ribosomes are termed as

Polysome is a string of ribosomes associated with a single mRNA. Polysome helps to produce a number of copies of the same polypeptide.

The nucleosome is the unit of eukaryotic DNA that consists of a DNA segment wrapped around a core of eight histone proteins. Nucleosome chain gives a 'beads on a string' appearance under an electron microscope. 

Plastidome refer to all the plastids of a cell which work as a functional unit.

Polyhedral bodies or carboxysomes are present in several groups of autotrophic bacteria that assimilate inorganic carbon via the Calvin cycle, e.g. Cyanobacteria.