Final answer:
Menopause is signaled by a marked drop in sex hormone production, causing ovulation and menstruation to stop.
Step-by-step explanation:
The marked drop in the production of sex hormones in a woman's bloodstream, which causes ovulation and menstruation to stop, is a signal of menopause. During menopause, a woman's ovaries lose their sensitivity to FSH and LH, leading to a decrease in menstrual periods and eventually their cessation. Without the stimulation of FSH and LH, the ovaries do not produce viable eggs, resulting in the inability to have children.