CBSE Class 10 Science 2020 · Paper 31/4/3 · Question 28(a)

(a) 1. Fertilisation takes place in the oviduct; the zygote formed divides and reaches the uterus as an embryo. 2. The uterus has prepared itself with a thick lining, richly supplied with blood to nourish the growing embryo, and the embryo gets implanted in it. 3. The embryo gets nutrition from the mother's blood with the help of a special tissue, the placenta: a disc embedded in the uterine wall, with villi on the embryo's side and blood spaces on the mother's side surrounding the villi. 4. Through the placenta, glucose and oxygen pass from the mother's blood to the embryo, and waste substances pass from the embryo to the mother's blood. 5. The child develops inside the mother's body for about nine months. 6. The child is born as a result of rhythmic contractions of the muscles of the uterus. (b) The thick and spongy lining of the uterus is not needed, so it breaks down and comes out through the vagina as blood and mucus. This is menstruation; it lasts about two to eight days and occurs about once a month.