Read the given passage and answer the following questions :
The average duration of human pregnancy is about 9 months which is called the gestation period. Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the foetus. This process of delivery of the foetus (childbirth) is called parturition. Parturition is induced by a complex neuroendocrine mechanism. The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex. This triggers release of oxytocin from the maternal pituitary. Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of oxytocin. The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions. This leads to expulsion of the baby out of the uterus through the birth canal – parturition. Soon after the infant is delivered, the placenta is also expelled out of the uterus. The mammary glands of the female undergo differentiation during pregnancy and starts producing milk towards the end of pregnancy by the process called lactation. This helps the mother in feeding the new- born. The milk produced during the initial few days of lactation is called colostrum which contains several antibodies absolutely essential to develop resistance for the new-born babies. Breast-feeding during the initial period of infant growth is recommended by doctors for bringing up a healthy baby.
The placenta is connected to the embryo through:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Umbilical cord
After implantation, finger-like chorionic villi grow from the trophoblast and interlock with the uterine tissue. Together they form the placenta, the structural and functional link between the foetus and the mother. The placenta is joined to the embryo by a cord that carries substances to and from the embryo.
Option (1) Chorionic villi — Incorrect. Chorionic villi are finger-like projections on the trophoblast. With the uterine tissue they form the placenta itself; they are not the link between the placenta and the embryo.
Option (2) Trophoblast — Incorrect. The trophoblast is the outer layer of cells of the blastocyst. It gets attached to the endometrium during implantation, and the chorionic villi later grow from it. It is not a connecting cord.
Option (3) Inner cell mass — Incorrect. The inner cell mass is the group of cells inside the blastocyst that becomes the embryo. It cannot be the structure that joins the embryo to the placenta.
Option (4) Umbilical cord — Correct. The placenta is connected to the embryo through the umbilical cord. It carries oxygen and nutrients to the embryo and takes carbon dioxide and wastes away from it.
NCERT Extract:
Pregnancy and Embryonic Development – “After implantation, finger-like projections appear on the trophoblast called chorionic villi which are surrounded by the uterine tissue and maternal blood. The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal body called placenta (Figure 2.12). The placenta facilitate the supply of oxygen and nutrients to the embryo and also removal of carbon dioxide and excretory/waste materials produced by the embryo. The placenta is connected to the embryo through an umbilical cord which helps in the transport of substances to and from the embryo.”