Which component is the soft inner part of bone?

• A. Periosteum
• B. Compact bone
• C. Cancellous bone
• D. Bone Marrow

Answer: (D)

The soft inner part of bone is bone marrow. It fills the medullary cavity and is not a mineralized, hard tissue like the surrounding bone. Bone marrow is soft because it contains fat cells and hematopoietic cells, and it serves to make blood cells (red marrow) or store fat (yellow marrow).

The other components are distinct: the periosteum is the tough outer membrane that covers bone; compact bone is the dense, hard outer layer that gives strength; cancellous bone is the spongy, lattice-like interior that is lighter and contains marrow spaces but is itself mineralized. So the term describing the soft inner tissue aligns with bone marrow.