White Blood Cells' Immune Functions

Steps:

• Recall white blood cells (leukocytes) defend against infection via phagocytosis, antibody production, and inflammation.
• Evaluate option A: Matches phagocytosis, where cells engulf bacteria.
• Check B: WBCs produce antibodies, not antigens.
• Assess C: Clotting involves platelets and plasma proteins, not WBCs.
• Verify D: Toxin transport relates to blood plasma or liver cells, not WBCs.

Why A is correct:

• Phagocytosis is the process by which white blood cells like neutrophils and macrophages engulf and destroy bacteria, as defined in immune response mechanisms.

Why the others are wrong:

• B: White blood cells produce antibodies to target antigens; antigens are foreign molecules from pathogens.
• C: Conversion of fibrinogen to fibrin is part of blood clotting by coagulation factors and platelets.
• D: White blood cells do not transport toxins; this occurs via bloodstream to liver for detoxification.

Final answer: A