In humans, which organ system is responsible for producing white blood cells?

• A. Immune system
• B. Skeletal system
• C. Circulatory system
• D. Lymphatic system

Answer: (A)

White blood cells come from the bone marrow, which is part of the skeletal system. In red bone marrow, hematopoietic stem cells differentiate into the different blood cells, including leukocytes, that circulate to defend the body. While the immune system, lymphatic system, and circulatory system all work with white blood cells, the production site is the bone marrow inside bones. So the skeletal system is responsible for producing white blood cells.