The capsid is the protein shell that encloses and protects the viral genetic material.

Viroids are smaller than viruses, consisting only of a short RNA strand without a protein coat.

Both viruses and viroids can contain RNA, but viruses may also have DNA, making the DNA-only statement not a valid difference.

T.O. Diener discovered viroids in 1971 while investigating potato spindle tuber disease.

Mumps, smallpox, and influenza are caused by viruses, whereas potato spindle tuber disease is caused by viroids.

HIV is an RNA virus (retrovirus), whereas adenoviruses, herpesviruses, and papillomaviruses have DNA genomes.

AIDS stands for Acquired Immuno Deficiency Syndrome, caused by HIV, leading to immune system failure.

In lichens, the fungal component is called the mycobiont, forming a symbiotic relationship with the algal phycobiont.

The envelope, a lipid bilayer derived from the host cell, allows some viruses to fuse with host cell membranes for entry.

Lichens are sensitive to air pollution and do not thrive in polluted environments, indicating pollution levels.

Viruses are non-living outside a host, lacking cellular structure and independent metabolic activities.

Animal viruses contain either single/double-stranded RNA or double-stranded DNA, but not both simultaneously.

Bacteriophages are viruses that infect bacteria, typically containing double-stranded DNA.

Most plant viruses have single-stranded RNA, enabling replication in plant cells.

The word 'Virus' derives from Latin, meaning venom or poison, as coined by Martinus Beijerinck.

Most viruses replicate in the cytoplasm, though some DNA viruses use the nucleus for transcription and replication.

Viruses cannot perform any metabolic activities outside a living host, making this statement incorrect.

The viral capsid, a protective sheath, is made of proteins.

W.M. Stanley crystallized tobacco mosaic virus, proving viruses can form crystalline structures.

Viruses are obligate parasites, requiring a host to replicate and perform metabolic activities.