AP BIOLOGY

Detailed explanation-1: -There are two conditions which can lead to menstruation in a 21-year-old woman during ovulation. These are: (i) Blocked oviduct and, (ii) sperms not available for fertilization.

Detailed explanation-2: -Longer cycles are caused by a lack of regular ovulation. During a normal cycle, it is the fall of progesterone that brings upon bleeding. If a follicle does not mature and ovulate, progesterone is never released and the lining of the uterus continues to build in response to estrogen.

Detailed explanation-3: -A period happens because of changes in hormones in the body. Hormones are chemical messengers. The ovaries release the female hormones estrogen and progesterone . These hormones cause the lining of the uterus (or womb) to build up.

Detailed explanation-4: -The egg travels down the fallopian tubes. If pregnancy doesn’t occur, the egg is reabsorbed into the body. Levels of oestrogen and progesterone fall, and the womb lining comes away and leaves the body as a period (the menstrual flow). The time from the release of an egg to the start of a period is around 10 to 16 days.

Detailed explanation-5: -Ovulation happens before the bleeding from a girl’s period has stopped. Ovulation happens within a few days after a girl’s period is over. Sperm can fertilize an egg for 3 days. So if a girl has sex on the last day of her period and ovulates in the next few days, the sperm may still fertilize the egg.