Answer: Because they show no signs of life outside a living host cell and are non-cellular.
- A Because their size is below the resolution limit of even electron microscopy
- B Because they show no signs of life outside a living host cell and are non-cellular
- C Because their host range is restricted largely to plant cells, excluding animals
- D Because they largely lack any form of nucleic acid genetic material
Correct answer: B. Because they show no signs of life outside a living host cell and are non-cellular
Explanation: Viruses are non-cellular, obligate intracellular parasites. Outside a host cell, they are inert and show no characteristics of life, so Whittaker's five kingdom system, based on cellular organisms, excludes them.
Whittaker's five-kingdom system (1969) groups all cellular life by cell structure and nutrition; viruses, viroids, and lichens fall outside this system entirely since they aren't independently classifiable as one of the five.
Concept context
Whittaker's five kingdom system covering Monera, Protista, Fungi, plus viruses, viroids, and lichens. A foundational NEET chapter on how living organisms are grouped.