Virus is defined as

Virus is defined as

• A. An extremely small particle that consists of an outer shell and genetic material
• B. A living cell that reproduces
• C. A type of bacteria
• D. A molecule that triggers allergies

Answer: (A)

Understanding what defines a virus is the key idea here. A virus is an extremely small particle that consists of an outer shell and genetic material. That structure—a protective protein coat around DNA or RNA—sets it apart from cells. Viruses aren’t living cells themselves; they lack cellular machinery and can’t reproduce on their own. Instead, they must hijack a host cell’s machinery to make new viral particles. The other descriptions refer to a living cell that can reproduce on its own, a bacterium, or a molecule that triggers allergies, none of which accurately define a virus.

Understanding what defines a virus is the key idea here. A virus is an extremely small particle that consists of an outer shell and genetic material. That structure—a protective protein coat around DNA or RNA—sets it apart from cells. Viruses aren’t living cells themselves; they lack cellular machinery and can’t reproduce on their own. Instead, they must hijack a host cell’s machinery to make new viral particles. The other descriptions refer to a living cell that can reproduce on its own, a bacterium, or a molecule that triggers allergies, none of which accurately define a virus.