Read the given passage and answer the following questions:
Spermatogenesis results in the formation of sperms that are transported by the male sex accessory ducts. A normal human sperm is composed of a head, neck, a middle piece and tail. The process of formation of mature female gametes is called oogenesis. The reproductive cycle of female primates is called menstrual cycle. Menstrual cycle starts only after attaining sexual maturation (puberty). During ovulation only one ovum is released per menstrual cycle. The cyclical changes in the ovary and the uterus during menstrual cycle are induced by changes in the levels of pituitary and ovarian hormones. After coitus, sperms are transported to the ampulla, where the sperm fertilises the ovum leading to formation of a diploid zygote. The presence of X or Y chromosome in the sperm determines the sex of the embryo. The zygote undergoes repeated mitotic division to form a blastocyst, which is implanted in the uterus resulting in pregnancy. After nine months of pregnancy, the fully developed foetus is ready for delivery. The process of childbirth is called parturition which is induced by a complex neuroendocrine mechanism involving cortisol, estrogens and oxytocin. Mammary glands differentiate during pregnancy and secrete milk after child-birth. The new-born baby is fed milk by the mother (lactation) during the initial few months of growth.
Which of the following is a function of the placenta?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Supply of oxygen and nutrients to the embryo and removal of carbon dioxide and excretory wastes
After implantation, finger-like chorionic villi grow out from the trophoblast. They and the uterine tissue interlock and together form the placenta, the link between the foetus and the mother’s body. Through the placenta the embryo receives oxygen and nutrients and gets rid of carbon dioxide and excretory wastes.
Option (1) Giving rise to all the tissues and organs of the embryo — Incorrect. All the tissues and organs of the embryo come from the inner cell mass. The placenta supports the embryo but does not form its organs.
Option (2) Supply of oxygen and nutrients to the embryo and removal of carbon dioxide and excretory wastes — Correct. This is the main job of the placenta: food and oxygen pass in, wastes pass out.
Option (3) Secretion of oxytocin, which causes strong uterine contractions during parturition — Incorrect. Oxytocin is released from the maternal pituitary. The fully developed foetus and the placenta only send signals. These cause mild uterine contractions (the foetal ejection reflex), which trigger its release at parturition.
Option (4) Differentiation into the ectoderm, mesoderm and endoderm of the embryo — Incorrect. The inner cell mass differentiates into the ectoderm, mesoderm and endoderm. The placenta comes from the trophoblast and the uterine tissue, not from the germ layers.
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.”