The document provides an overview of physical and psychological changes that occur during adolescence, including: - Rapid growth and development of primary and secondary sex characteristics due to increases in sex hormones. - Differences in the timing of puberty between boys and girls, with girls starting earlier on average. - Changes in body composition with increases in body fat and muscle. - Brain development continuing into early twenties with improvements in cognitive abilities. - Health risks such as obesity, eating disorders, drug and alcohol use that can arise during this transitional life stage.