Final answer:
The epiphyseal plate closes around age 18-21 due to bone replacing cartilage and the cessation of cartilage cell division. This process results in the fusion of the epiphysis and diaphysis.
Step-by-step explanation:
The closure of the epiphyseal plate around age 18-21 is prompted by the process of bone replacing cartilage and the cessation of cartilage cell division. This process results in the fusion of the epiphysis and diaphysis, creating a structure called the epiphyseal line or remnant.
This closure marks the end of longitudinal bone growth in long bones. It occurs at a later age in males compared to females, with closure typically happening around age 21 in males and age 18 in females.