Boys often start the changes caused by puberty a year or two later than girls. A boy's voice will become deeper, hair grows on his body and face and he will start to produce sperm. Adolescent girls and boys have a strong interest in their own sexual development and become more curious about the opposite sex. Becoming a woman Hormones cause a girl's body to develop into that of a woman. Her hips grow wider to make room for a baby to develop in her womb and to be born through her vagina.
Breasts form that, after pregnancy, produce milk to feed the baby.
Her ovaries release one or more eggs during each menstrual cycle. She grows hair in her armpits and in the pubic region of her body. Becoming a man Hormones cause a boy's body to develop into that of a man. His body becomes muscular and his penis and testes grow larger. His penis, when erect, can enter a woman's vagina to provide sperm from his testes to fertilize an egg.