Which type of white blood cell defends against microorganisms and makes up about 75% of white blood cells?

• A. Monocytes
• B. Lymphocytes
• C. Granulocytes
• D. Erythrocytes

Answer: (C)

Granulocytes are the white blood cell group that handles the initial defense against invading microorganisms. They contain granules filled with enzymes and antimicrobial substances and are highly mobile, quickly moving to sites of infection to engulf and destroy bacteria and fungi (phagocytosis) and release killing chemicals. This frontline role plus their high numbers in the blood explains why they make up the largest share of white blood cells—about three-quarters in many samples. The other options represent different immune roles or cells that don’t contribute to the bulk, such as monocytes (fewer in number and become macrophages), lymphocytes (adaptive immune responders), and erythrocytes (red blood cells, not part of the immune defense).