Why must animal viruses enter host cells to replicate?

• A. Because viruses can only obtain nutrients from inside host cells
• B. Because viruses need to avoid detection by the immune system
• C. Because viruses lack the cellular machinery necessary for independent replication
• D. Because viruses require host cell walls for attachment

Answer: (C)

Verified step by step guidance

1. Understand that viruses are obligate intracellular parasites, meaning they cannot reproduce outside a host cell.
2. Recognize that viruses lack essential cellular components such as ribosomes and enzymes needed for processes like transcription and translation.
3. Know that because of this lack, viruses must enter host cells to use the host's cellular machinery to replicate their genetic material and produce viral proteins.
4. Evaluate the given options by comparing them to the fundamental biology of viruses, focusing on their dependence on host cell machinery rather than nutrient acquisition or immune evasion.
5. Conclude that the correct reason is that viruses lack the cellular machinery necessary for independent replication, which is why they must enter host cells.