Final answer:
Menarche is the beginning of menstrual periods in girls, usually occurring around the age of 12 or 13. Menopause, on the other hand, marks the end of menstrual cycles in women, typically around the age of 50.
Step-by-step explanation:
Menarche refers to the first menstrual period that occurs in girls, typically around the age of 12 or 13. Menopause, on the other hand, marks the end of menstrual periods in women, usually around the age of 50. Menopause is characterized by the gradual cessation of menstrual cycles, as the ovaries stop releasing eggs.