Final answer:
Long bones and bony projections increase in length due to the activity at the epiphyseal plate, where chondrocytes divide and mature, resulting in bone lengthening.
Step-by-step explanation:
Long bones and bony projections increase in length because of growth at the epiphyseal plate. The process of bone lengthening involves chondrocytes, cells found in cartilage, which divide on the epiphyseal side of the epiphyseal plate. As these cells mature, they move toward the diaphysis, where they are eventually replaced by ossified tissue. This results in the bone extending further at each end. These cells replace cartilage with bone on the diaphyseal side, leading to the lengthening of the bone. Once a person reaches early adulthood (approximately 18-21 years), the bone ceases to grow as the cartilage is fully replaced by bone, and the epiphyseal plate becomes the epiphyseal line.