Ossification- Blood vessels deposit calcium and phosphorus in the cartilage, turning it to bone.
Can tell whether someone is growing by the quantity of cartilage present
Osteoporosis can be treated with calcium supplements
Simple structure of the bone: Shaft, cartilage layer, compact bone, and bone marrow (which produces red blood cells)
Internal skeleton has advantages; can easily grow with body, easily attach muscles to it, more flexible than external skeleton.
Broken bone can also affect nearby tissue.