Which of the following is a basic characteristic of viruses?

• A. They contain ribosomes and generate ATP through their own metabolism.
• B. They are single-celled organisms that reproduce by binary fission.
• C. They are obligate intracellular parasites that require a host cell to replicate.
• D. They can grow on nutrient agar as independent colonies.

Answer: (C)

Verified step by step guidance

1. Understand the nature of viruses: Viruses are unique infectious agents that differ fundamentally from cellular life forms such as bacteria and fungi.
2. Recall that viruses lack cellular structures like ribosomes and do not carry out metabolic processes such as ATP generation on their own.
3. Recognize that viruses cannot reproduce independently; instead, they must infect a host cell and use the host's machinery to replicate.
4. Note that viruses do not grow on nutrient agar or form colonies like bacteria because they are not living cells capable of independent growth.
5. Conclude that the defining characteristic of viruses is that they are obligate intracellular parasites, meaning they require a host cell to replicate.