6 public questions tagged with this topic.
Viruses are considered living only when inside a host ll, where they use the host’s machinery to replicate. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
Cell-mediated immunity, mediated by T-cells, is responsible for eliminating intracellular pathogens like viruses.
Ref: NCERT Class 12 Biology Chapter 7: Human Health and Disease Immunity - Innate Immunity - Barriers and Interferons
Diphtheria is caused by the bacterium Corynebacterium diphtheriae, whereas the others are viral diseases.
Ref: NCERT Class 12 Biology Chapter 7: Human Health and Disease Common Diseases - Viral - Common Cold and Other Viral Diseases
Viruses are inert outside their specific host cells. After infecting a living cell, they take over the host-cell machinery to produce new viral particles; therefore, they are obligate parasites.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Bacteria - Structure and Economic Importance
Viral genetic material displays remarkable diversity compared to cellular life that universally uses double-stranded DNA. Viruses package either DNA or RNA in single- or double-stranded form, linear or circular, segmented or monopartite, employing diverse replication strategies. Some dsDNA viruses replicate via host polymerases, RNA viruses require RNA-dependent RNA polymerase, retroviruses reverse transcribe RNA into DNA. Neither DNA alone nor RNA alone describes entire virosphere. Classification systems including Baltimore classification categorize viruses based on genome type and replication intermediate, reflecting that genome can be either nucleic acid.
Ref: Baltimore D., Nobel Lecture 1975: Virus Genome Can Be DNA or RNA, Classification of Viruses
The physical nature of viruses was a mystery until 'W.M. Stanley' in 1935 biochemically manipulated them. The NCERT textbook highlights his discovery that viruses could actually be 'crystallised', and these biological crystals consisted almost entirely of tightly packed proteins. This proved they were inert outside a host, cementing their status as non-cellular obligate parasites lying on the boundary of living and non-living.
Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens
