The document discusses adolescence and puberty. During adolescence, between ages 11-19, the body undergoes significant physical changes in preparation for reproductive maturity. This period of development is called puberty. Some of the key physical changes discussed include increased height, changed body shape, voice changes, development of secondary sex characteristics like facial hair or breasts, and full development of sex organs. Hormonal changes triggered by the pituitary and other glands facilitate these physical transformations. The document also covers reproductive health, sex determination, menstruation, and risks of drug use and HIV/AIDS.