Which of the following is a characteristic of a virus?

• A. It requires a host cell for replication
• B. It contains both DNA and RNA in its genome
• C. It can reproduce independently in the environment
• D. It is composed only of proteins without any nucleic acids

Answer: (A)

Verified step by step guidance

1. Step 1: Understand what a virus is — a virus is a microscopic infectious agent that can only replicate inside the living cells of an organism.
2. Step 2: Analyze the options given: viruses do not contain both DNA and RNA simultaneously; they have either DNA or RNA as their genetic material, but not both.
3. Step 3: Recognize that viruses cannot reproduce independently in the environment because they lack the cellular machinery necessary for replication.
4. Step 4: Know that viruses are composed of nucleic acids (DNA or RNA) enclosed in a protein coat called a capsid, so they are not made only of proteins.
5. Step 5: Conclude that the defining characteristic of viruses is their requirement for a host cell to replicate, as they rely entirely on the host's cellular machinery.