CBSE Class 10 Science 2022 · Paper 31/2/1 · Question 3

(i) The embryo gets its nutrition from the mother’s blood through the placenta, a disc embedded in the uterine wall. The placenta has villi on the embryo’s side surrounded by blood spaces on the mother’s side, giving a large surface area through which glucose and oxygen pass from the mother to the embryo, and the embryo’s waste substances pass into the mother’s blood to be removed. Without the placenta the foetus could not obtain food and oxygen or get rid of its wastes, so it could not develop. (ii) After fertilisation the zygote is implanted in the lining of the uterus. The lining is thick, spongy and richly supplied with blood so that it can receive the embryo and nourish it as it grows; the placenta develops in it. (The uterus prepares this lining every month; if the egg is not fertilised, the lining breaks down and is shed in menstruation.)