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PCAT Biological Processes – Complement System of the Blood

Which of the following is NOT a function of the complement system of the blood?


A) Aiding the immune response by selectively binding to specific foreign antigens.

B) Increasing opsonization by enhancing the phagocytosis of foreign antigens.

C) Using a chemotaxis effect to attract greater numbers of macrophages and neutrophils to an infection site.

D) Directly lysing cells by rupturing the cell membranes of foreign cells.



The complement system is a group of proteins found in the blood and is a part of the innate immune system, which does not change over a person’s lifetime and does not react to specific antigens, but rather provides broad defenses against many types of foreign cells or substances. As such, it does not selectively bind to specific antigens as (A) says – this is the function of antibodies produced by B cells. Thus (A) is the correct answer.

The remaining choices are all functions of the complement system.

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