(i) (a) Implantation: Implantation is the process of attachment of the developing embryo or the fertilized egg with the uterine wall.
(b) Placenta: A disc-shaped special tissue develops between the wall of the uterus and the embryo for exchange of nutrients, supply of oxygen and excretion of waste products.
(ii) The average duration of human pregnancy is 280 days or 40 weeks or 9 months.
