Final answer:
Appositional growth is the increase in bone diameter through the addition of bony tissue at the surface of bones. Osteoblasts secrete bone matrix, while osteoclasts break down bone to maintain the balance between bone formation and destruction.
Step-by-step explanation:
Appositional growth is the process by which bones increase in diameter by adding bony tissue at the surface of the bones. Osteoblasts, which are cells on the bone surface, secrete bone matrix, while osteoclasts, located on the inner surface of the bone, break down bone. This balance between bone formation and bone destruction allows bones to thicken without becoming too heavy.