Bone marrow produces which of the following?

• A. Spongy bone
• B. Blood cells
• C. Calcium and phosphorus
• D. Peritoneum

Answer: (B)

Bone marrow is the site of hematopoiesis, the production of blood cells. Through this process, hematopoietic stem cells differentiate into all blood cell types—red blood cells that carry oxygen, white blood cells that defend against infection, and platelets that help with clotting. This activity is what makes bone marrow the source of blood cells, not of structural bone tissue, minerals stored in the bone matrix, or the lining of the abdominal cavity. In adults, red marrow remains the active site for blood cell production, while yellow marrow mainly stores fat and isn’t a major site of hematopoiesis unless needed.