The tissue in bones that produces red blood cells, platelets, and some white blood cells is called:

• A. Red marrow
• B. Yellow marrow
• C. Bone matrix
• D. Endosteum

Answer: (A)

Red bone marrow is the tissue that carries out hematopoiesis, the production of blood cells. It contains hematopoietic stem cells that mature into red blood cells, platelets, and some white blood cells. In adults, red marrow is located in the cancellous (spongy) bone of the pelvis, sternum, ribs, vertebrae, and the ends of long bones. Yellow marrow, by contrast, stores fat and is not involved in active blood cell production. The bone matrix is the mineralized framework that gives bone its strength, and the endosteum lines the inner bone surfaces and contains cells important for bone growth and repair. Because this tissue’s primary role is forming blood cells, it is red marrow.