Read the following statements concerning the luteal phase of the menstrual cycle:
(I) During the luteal phase, the remaining parts of the Graafian follicle transform into the corpus luteum. (II) The corpus luteum secretes large amounts of progesterone, which is essential for endometrial maintenance. (III) An intact endometrium is necessary for the implantation of a fertilized ovum. (IV) In the presence of fertilization, the corpus luteum rapidly degenerates, causing menstruation.
Explanation: Statements (I), (II), and (III) are correct. Statement (IV) is incorrect because the corpus luteum degenerates only in the absence of fertilization, leading to menstruation.
Question 22 of 100
📘 CLASS XII
Choose the correct statements regarding fertilisation in humans:
(I) Fertilisation can only occur if the ovum and sperms are transported simultaneously to the ampullary region. (II) During fertilisation, a sperm comes in contact with the corona radiata layer to block polyspermy. (III) The secretions of the acrosome help the sperm enter the cytoplasm of the ovum. (IV) The block to polyspermy ensures that only one sperm can fertilise an ovum.
Explanation: Statements (I), (III), and (IV) are correct. Statement (II) is incorrect because the sperm first interacts with the zona pellucida, which undergoes changes to block polyspermy.
Question 23 of 100
📘 CLASS XII
Read the statements concerning the completion of meiotic division in the female gamete:
(I) Sperm entry into the ovum cytoplasm induces the completion of the second meiotic division. (II) The second meiotic division is an equal division yielding two identical ootids. (III) This division results in the formation of a second polar body and a haploid ovum (ootid). (IV) The haploid nucleus of the sperm and that of the ovum fuse to form a diploid zygote.
Explanation: Statements (I), (III), and (IV) are correct. Statement (II) is incorrect because the second meiotic division is unequal, producing a large ovum and a small second polar body.
Question 24 of 100
📘 CLASS XII
Identify the correct statements regarding early embryonic development and cleavage:
(I) Cleavage division starts as the zygote moves through the isthmus toward the uterus. (II) Blastomeres are the daughter cells formed during these rapid mitotic divisions. (III) An embryo with 8 to 16 blastomeres is called a morula. (IV) The morula immediately implants itself into the uterine wall.
Explanation: Statements (I), (II), and (III) are correct. Statement (IV) is incorrect because the morula develops into a blastocyst, and implantation is carried out by the blastocyst through its trophoblast.
Question 25 of 100
📘 CLASS XII
Which of the following statements regarding the placenta and pregnancy hormones are correct?
(I) Finger-like projections on the trophoblast after implantation are called chorionic villi. (II) The placenta acts as an endocrine tissue, producing hCG, hPL, estrogens, and progestogens. (III) Relaxin is a hormone secreted by the pituitary gland during early pregnancy. (IV) hCG, hPL, and relaxin are produced in women only during pregnancy.
Explanation: Statements (I), (II), and (IV) are correct. Statement (III) is incorrect because relaxin is secreted by the ovary during the later phase of pregnancy, not by the pituitary gland.
Question 26 of 100
📘 CLASS XII
Which of the following statements regarding the hormone relaxin are biologically accurate?
(I) It is synthesized and secreted by the anterior pituitary gland to soften the pubic symphysis during delivery. (II) In human females, it is produced exclusively during the gestational period. (III) Its secretion occurs primarily during the late phase of pregnancy. (IV) It acts synergistically with luteinizing hormone to maintain the corpus luteum in non-pregnant cycles.
Explanation: Statement (I) is incorrect because relaxin is secreted by the ovary, not the anterior pituitary. Statements (II) and (III) are correct. Statement (IV) is incorrect because relaxin is not involved in maintaining the corpus luteum in normal menstrual cycles.
Question 27 of 100
📘 CLASS XII
Examine the following statements regarding fetal developmental milestones during pregnancy:
(I) The formation of the embryo's heart is completed by the end of the second month of gestation. (II) Limbs and digits develop by the end of the second month of pregnancy. (III) By the end of 12 weeks, major organ systems such as the limbs and external genital organs are well-formed. (IV) The first movements of the fetus and appearance of head hair are typically observed during the fifth month.
Explanation: Statement (I) is incorrect because the embryo's heart is formed after one month of pregnancy. Statements (II), (III), and (IV) are correct developmental milestones.
Question 28 of 100
📘 CLASS XII
Concerning the physiological changes during pregnancy, analyze these statements:
(I) Maternal blood levels of estrogens and progestogens increase several-fold to support fetal growth. (II) Cortisol, prolactin, and thyroxine levels remain completely unchanged in maternal blood to prevent systemic toxicity. (III) Increased hormone levels are vital for supporting metabolic changes in the mother. (IV) Maintenance of pregnancy depends heavily on the elevated levels of these maternal hormones.
Explanation: Statement (II) is incorrect because maternal blood levels of cortisol, prolactin, and thyroxine increase several-fold during pregnancy. Statements (I), (III), and (IV) are correct.
Question 29 of 100
📘 CLASS XII
Read the statements below regarding the structural features of the placenta:
(I) The chorionic villi and uterine tissue become interdigitated with each other. (II) They form a structural and functional unit between the developing embryo and the maternal body. (III) The placenta is connected to the embryo through a follicular duct. (IV) The connecting structure helps in transporting substances to and from the developing embryo.
Explanation: Statements (I), (II), and (IV) are correct. Statement (III) is incorrect because the placenta is connected to the embryo through the umbilical cord, not a follicular duct.
Question 30 of 100
📘 CLASS XII
Consider the following events of parturition and identify the correct combination:
(I) Parturition is induced by a complex neuroendocrine mechanism. (II) The signals for child delivery originate exclusively from the maternal pituitary gland. (III) The mild uterine contractions induced by the fetus and placenta are called the fetal ejection reflex. (IV) This reflex triggers the release of prolactin from the maternal pituitary gland.
Explanation: Statements (I) and (III) are correct. Statement (II) is incorrect because the signals originate from the fully developed fetus and placenta. Statement (IV) is incorrect because the fetal ejection reflex stimulates the release of oxytocin, not prolactin.
