Question

Difference between virus and viroid is:
(a) Absence of protein coat in viroid but present in the virus
(b) Presence of low molecular weight RNA in the virus but absent in viroids
(c) Both (a) and (b)
(d) None of these

Answer 1

Hint: Both the virus and viroids are infectious agents and nonliving until they invade a live host cell. They differ based on the type of their genetic material and the target cells they infect.

Complete answer:
Differences between virus and viroids are:

Features	Virus	Viroid
Nucleic acid	The genetic material is both DNA or RNA. DNA is double-stranded while RNA can be both single-stranded or double-stranded.	Their genetic material is composed of single stranded low molecular weight RNA.
Capsid	A protein coat or capsid is present.	The protein coat or capsid is absent.
Protein	It manufactures proteins and enters the host cell.	Viroid RNA does not code for any proteins.
Host	They infect bacteria, plants and animals.	They infect only plants.

So, the correct answer is ‘Absence of protein coat in viroid but present in the virus.’

Additional Information:
The important features of the virus are:
 - The structure of the virus is varied in terms of size, shape, and chemical composition. These obligate intracellular parasites are smaller than prokaryotic cells ranging in size from 0.02 to 0.3μm.
 - A fully assembled infectious virus is termed as a virion.
 - Every virus contains a protein coat or capsid which functions as a shell to protect the viral genome from nucleases. It also helps in its attachment to specific receptors on the host cell during infection.
 - The individual proteins building the capsid are called capsomeres.
 - The nucleic acid along with the capsid forms nucleocapsid.
 - Some viruses have an additional membranous envelope surrounding the nucleocapsid. They are known as enveloped viruses while those in which such an envelope is absent are termed as naked viruses.

Note: A group of viruses with RNA genome carrying reverse transcriptase is known as retroviruses. They make a DNA copy of their genome upon invading a host cell. E.g. Human Immunodeficiency Virus (HIV) causes AIDS or Acquired Immunodeficiency Syndrome in Humans.
Potato Spindle Tuber Viroid infects the tubers of potatoes, leading to its malformation and stunted growth in potato spindle tuber disease.