Basics of virology — What are bacteriophages?

Introduction / Context:
Bacteriophages, often called phages, are viruses that specifically infect bacteria. They are critical tools in molecular biology and play major ecological roles in controlling bacterial populations and facilitating gene transfer.

Given Data / Assumptions:

• Question seeks the correct definition of “bacteriophage.”
• Options include host immune cells, bacteria themselves, and viruses of bacteria.
• Focus is on classification, not life cycle details.

Concept / Approach:
A virus is an obligate intracellular parasite that replicates only within living cells. Bacteriophages recognize bacterial receptors, inject nucleic acid, and use bacterial machinery to replicate. Lytic phages lyse the host; temperate phages can integrate as prophages (lysogeny).

Step-by-Step Solution:

Verification / Alternative check:
Phage therapy and CRISPR discovery (from anti-phage immunity) underscore that phages target bacteria specifically.

Why Other Options Are Wrong:

• Blood cells that “eat” bacteria are phagocytes (e.g., neutrophils, macrophages), not bacteriophages.
• Bacteriophages are not bacteria; they lack cellular structure and metabolism.
• “None” is incorrect because a precise definition exists.

Common Pitfalls:
Confusing “phage” with “phagocyte” due to similar roots; remember, phages are viruses, phagocytes are immune cells.

Final Answer:
Bacterial viruses (viruses that infect bacteria)