The following are major steps in the process of endochondral ossification. 1. Blood vessels invade the perichondrium. 2. Osteoclasts create a marrow cavity. 3. Chondrocytes enlarge and calcify. 4. Osteoblasts replace calcified cartilage with spongy bone. 5. The perichondrium is converted into a periosteum and the inner layer produces bone The correct order for these events is __ 1,5,3,4,2 2,3,1,5,4 1,3,5,4,2 3,1,4,5,2 3,1,5,4,2

The correct order for these events is $3,1,5,4,2$.<br /><br />Explanation:<br />1. Chondrocytes enlarge and calcify: This is the first step in endochondral ossification, where the cartilage cells enlarge and become calcified.<br />2. Blood vessels invade the perichondrium: After the chondrocytes enlarge and calcify, blood vessels invade the perichondrium, which is the connective tissue surrounding the cartilage.<br />3. The perichondrium is converted into a periosteum and the inner layer produces bone: The perichondrium is converted into a periosteum, which is a membrane that covers the outer surface of the bone. The inner layer of the periosteum then produces bone.<br />4. Osteoblasts replace calcified cartilage with spongy bone: Osteoblasts, which are bone-forming cells, replace the calcified cartilage with spongy bone.<br />5. Osteoclasts create a marrow cavity: Osteoclasts, which are bone-resorbing cells, create a marrow cavity by breaking down bone tissue, allowing for the formation of the medullary cavity.