Which step of phagocytosis involves lysosomes fusing with phagosomes?

• A. Adherence
• B. Ingestion
• C. Digestion
• D. Killing

Answer: (C)

The process of phagocytosis is a crucial part of the immune response, whereby immune cells such as macrophages and neutrophils engulf and destroy pathogens or debris. The correct answer, which relates to the step where lysosomes fuse with phagosomes, is digestion.

During phagocytosis, once a pathogen has been engulfed into a phagosome (a membrane-bound vesicle), the next step involves the fusion of this phagosome with lysosomes. Lysosomes contain various enzymes and antimicrobial substances that break down proteins, lipids, and carbohydrates. This fusion results in the formation of a phagolysosome, where the enzymes from the lysosomes digest the engulfed material, effectively breaking it down into smaller pieces.

This step is vital because it transforms the ingested material into components that can either be co-opted for use by the immune cell or eliminated from the body, thus playing a key role in the immune response to infection and tissue repair. Therefore, the digestion phase is essential for ensuring that the immune cells can effectively neutralize threats posed by pathogens.