Which of the following protects the bone, assists in fracture repair, and is essential for oppositional growth? WHY? A) Articular cartilage B) Diaphysis C) Endosteum D) Epiphyses E) Periosteum

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Let's go through each of the choices in turn.  Articular cartilage is cartilage that is found on the surface of the ends of bones between bone joints.  The diaphysis is the central shaft section of a bone that surrounds the marrow.  The endosteum is a thin layer of connecting tissue that lines the inner cavity in a bone called the medullary cavity.  The epiphysis is the rounded end of a bone where it forms joints with other bones.  Finally, the periosteum is a fiberous membrane that covers the outer surface of most bones.  This is what offers protection to the bone underneath.  It also contains the blood vessels, so it helps nourish the bone cells with blood supply.  The periosteum also contains osteoblasts, which are cells that produce more bone material.  So when a fracture occurs, the osteoblasts multiply in number and begin laying new bone material to mend the fracture.  So the answer to your question is periosteum.

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