Final answer:
The areas of increased activity on bone images of adults are the epiphyseal plates. The epiphyseal plate is responsible for lengthwise growth of long bones until adolescence.
Step-by-step explanation:
The areas of increased activity on bone images of adults are the plates.
The epiphyseal plate is the area of growth in a long bone, where cartilage is formed on the epiphyseal side and ossified on the diaphyseal side.
It is responsible for lengthwise growth of long bones until adolescence, when it is replaced by osseous tissue and becomes an epiphyseal line.