Section 1 Introduction - is a time of major transition that bridges the gap between childhood and adulthood. This developmental stage is marked by significant biological changes that can make the teenage years incredibly challenging. As their bodies continue to rapidly mature, many adolescents struggle to make sense of their changing world. The changes that adolescents experience in the biosocial domain include the following: puberty, brain development, physical development, and sexuality. In this section, we will examine the developmental milestones that contribute to children’s bodies transforming into adult bodies that are capable of reproduction.