Question

define virus, virion and viroid and explain the differences.

Answer 1

Virus: Acellular entity that, although it can live extracellularly, is an absolut parasite, because it's only capable to replicate in the specific living cells lap, but without generating energy or any other metabolic activity. The permanent components of the virus are DNA or RNA (one or two chains) wrapped by a protein cover called capsid.
Virion: Structural unit of the virus; has two essential structures: DNA or RNA and capsid. Sometimes, a peplum and/or glycoprotein spicules can be added to these basic structures.
Viroid: Causal agent of several plant diseases, called viroid because of its similarity with virus, with the DIFFERENCE that virus has capsid, unlike viroid. We're talking about a nucleic acid covered by a membrane from the cell where it replicated. By extension, it was applied to what today we know as 'prions'.