Which structure protects a bacterial cell from ingestion and destruction by white blood cells (phagocytosis)?

• A. Endospore
• B. Capsule
• C. Flagella
• D. Pili

Answer: (B)

A capsule acts as a protective cloak around many bacteria, making them harder targets for white blood cells. It creates a slippery surface and can mask surface molecules that normally trigger immune recognition. This reduces opsonization—where antibodies and complement coat the bacteria to mark them for ingestion—and makes it more difficult for phagocytes to grab and engulf the pathogen. As a result, encapsulated bacteria can persist longer in the host and contribute to disease. Other structures have different roles: endospores are dormant, highly resistant forms; flagella enable movement; pili help with attachment or gene transfer. The capsule is the feature most directly linked to evading phagocytosis.