(a) When implantation has occured in uterus of the mother, the inner lining of the uterus thickens and is richly supplied with the blood vessels to provide nourishment to the growing embryo.
(b) If the egg is not fertilised, it lives for about one day. Since, the thickened uterus lining is no more required, it will slowly breakdown and comes out through the vagina as blood and mucous known as menstruation which lasts for about two to eight days.