State the changes that take place in the uterus when :
(i) Implantation of embryo has occurred.
(ii) Female gamete/egg is not fertilized.

Explanation

(i) When implantation of embryo has occurred the uterine wall thickens and is richly supplied with blood to nourish the growing embryo.
(ii) The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucous.
Detailed Answer :
(i) When implantation has occurred in uterus of mother, the inner lining of the uterus thickens and is richly supplied with the blood vessels to provide nourishment to the growing embryo.
(ii) If the egg is not fertilized, it lives for one day. Since, the thickened uterus lining is no more required, it slowly breaks down and comes out of the vagina as blood and mucous known as menstruation which lasts for about two to eight days.