Which organ system involves blood and blood-forming tissues?

• A. Hematologic
• B. Digestive
• C. Immune
• D. Endocrine

Answer: (A)

This question is about which bodily system is defined by blood and the tissues that form blood. The hematologic system covers blood itself and blood-forming tissues like bone marrow, plus organs such as the spleen and liver that participate in blood formation in some contexts. It includes the components of blood—red cells, white cells, platelets, and plasma—and handles the creation and circulation of these cells, oxygen transport, immunity, and clotting.

The other systems are focused on different roles: the digestive system for breaking down and absorbing nutrients, the immune system for defense (though immune cells travel in blood, the system name isn’t about blood formation), and the endocrine system for hormonal signaling.