NEET AIPMT Biology Chapter Wise Solutions – Human Reproduction
1. In human females, meiosis-II is not completed until
(a) uterine implantation
(d) fertilisation. (AIPMT 2015)
2. Which of the following layers in an antral follicle is acellular?
(b) Zona pellucida
(d) Theca interna (AIPMT 2015)
3. Which of the following events is not associated with ovulation in human female?
(a) Release of secondary oocyte
(b) LH surge
(c) Decrease in estradiol
(d) Full development of Graafian follicle (AIPMT 2015)
4. Ectopic pregnancies are referred to as
(a) implantation of defective embryo in the uterus
(b) pregnancies terminated due to hormonal imbalance
(c) pregnancies with genetic abnormality
(d) implantation of embryo at site other than uterus. (AIPMT 2015)
5. Which of the following cells during gametogenesis is normally diploid ?
(b) Secondary polar body
(c) Primary polar body
(d) Spermatid (AIPMT 2015, Cancelled)
6. Capacitation refers to changes in the
(a) ovum after fertilisation
(b) sperm after fertilisation
(c) sperm before fertilisation
(d) ovum before fertilisation. (AIPMT 2015, Cancelled)
7. Hysterectomy is surgical removal of
(a) vas deferens
(b) mammary glands
(d) prostate gland. (AIPMT 2015, Cancelled)
8. Which of these is not an important component of initiation of parturition in humans?
(a) Release of oxytocin
(b) Release of prolactin
(c) Increase in estrogen and progesterone ratio
(d) Synthesis of prostaglandins (AIPMT2015, Cancelled)
9. The shared terminal duct of the reproductive and urinary system in the human male is
(c) vas deferens
(d) vasa eflerentia. (AIPMT 2014)
10. The main function of mammalian corpus luteum is to produce
(a) estrogen only
(c) human chorionic gonadotropin
(d) relaxin only. (AIPMT 2014)
11. Select the correct option describing gonadotropin activity in a normal pregnant female.
(a) High level of FSH and LH stimulates the thickening of endometrium.
(b) High level of FSH and LH facilitates implantation of the embryo.
(c) High level of hCG stimulates the synthesis of estrogen and progesterone.
(d) High level of hCG stimulates the thickening of endometrium. (AIPMT 2014)
12. What is the correct sequence of sperm formation?
(a) Spermatogonia, spermatozoa, spermatocytes, spermatids
(b) Spermatogonia,spermatocytes, spermatids, spermatozoa
(c) Spermatids, spermatocytes, spermatogonia, spermatozoa
(d) Spermatogonia, spermatocytes, spermatozoa, spermatids (NEET 2013)
13. Which one of the following is not the function of placenta?
(a) F acilitates removal of carbon dioxide and waste material from embryo.
(b) Secretes oxytocin during parturition
(c) Facilitates supply of oxygen and nutrients to embryo.
(d) Secretes oestrogen. (NEET 2013)
14. Menstrual flow occurs due to lack of
(d) FSH. (NEET 2013)
15. The figure shows a section of human ovary. Select the option which gives the correct identification of either A or B with function/characteristic.
(a) B- Corpus luteum – Secretes progesterone
(b) A- Tertiary follicle – Forms Graafian follicle
(c) B- Corpus luteum – Secretes estrogen
(d) A- Primary oocyte – It is in the prophase-I of the meiotic division (Karnataka NEET 2013)
16. In our society women are blamed for producing female children. Choose the correct answer for the sex-determination in humans.
(a) Due to some defect like aspermia in man
(b) Due to the genetic make up of the particular sperm which fertilizes the egg
(c) Due to the genetic make up of the egg
(d) Due to some defect in the women (Karnataka NEET 2013)
17. The foetal ejection reflex in humans triggers the release of
(a) oxytocin from foetal pituitary
(b) human chorionic gonadotropin (hCG) from placenta
(c) human placental lactogen (hPL) from placenta
(d) oxytocin from maternal pituitary. (Karnataka NEET 2013)
18. Which one of the following statements is false in respect of viability of mammalian sperm?
(a) Sperm is viable for only up to 24 hours.
(b) Survival of sperm depends on the pH of the medium and is more active in alkaline medium.
(c) Viability of sperm is determined by its motility.
(d) Sperms must be concentrated in a thick suspension. (Prelims 2012)
19. Signals for parturition originate from
(a) both placenta as well as fully developed foetus
(b) oxytocin released from maternal pituitary
(c) placenta only
(d) fully developed foetus only. (Prelims 2012)
20. In a normal pregnant woman, the amount of total gonadotropin activity was assessed. The result expected was
(a) high level of circulating F SH and LH in the uterus to stimulate implantation of the embryo
(b) high level of circulating hCG to stimulate endometrial thickening
(c) high levels of FSH and LH in uterus to stimulate endometrial thickening
(d) high level of circulating hCG to stimulate estrogen and progesterone synthesis. (Prelims 2012)
21. The Leydig’s cells as found in the human body are the secretory source of
(b) intestinal mucus
(d) androgens(Prelims 2012)
22. Identify the human developmental stage shown below as well as the related right place of its occurrence in a normal pregnant woman, and select the right option for the two, together.
Developmental Site of occurrence stage
(a) Late morula – middle part of Fallopian tube
(b) Blastula – end part of Fallopian tube
(c) Blastocyst – uterine wall
(d) 8-celled morula – starting point of Fallopian tube (Mains 2012)
23. The secretory phase in the human menstrual cycle is also called
(a) luteal phase and lasts for about 6 days
(b) follicular phase and lasts for about 6 days
(c) luteal phase and lasts for about 13 days
(d) follicular phase and lasts for about 13 days. (Mains 2012)
24. If for some reason, the vasa efferentia in the human reproductive system get blocked, the gametes will not be transported from
(a) testes to epididymis
(b) epididymis to vas deferens
(c) ovary to uterus
(d) vagina to uterus (Prelims 2011)
25. The testes in humans are situated outside the abdominal cavity inside a pouch called scrotum. The purpose served is for
(a) maintaining the scrotal temperature lower than the internal body temperature
(b) escaping any possible compression by the visceral organs
(c) providing mere space for the growth of epididymis
(d) providing a secondary sexual feature for exhibiting the male sex. (Prelims 2011)
26. The figure given below depicts a diagrammatic sectional view of the human female reproductive system. Which set of three parts out of I-VI have been correctly identified?
(a) (II) endometrium, (III) infundibulum, (IV) fimbriae
(b) (III) infundibulum, (IV) fimbriae, (V) cervix
(c) (IV) oviducal funnel, (V) uterus, (VI) cervix
(d) (I) perimetrium, (II) myometrium, (III) Fallopian tube (Prelims 2011)
27. What happens during fertilization in humans after many sperms reach close to the ovum?
(a) secretions of acrosome helps one sperm enter cytoplasm of ovum through zona pellucida
(b) all sperms except the one nearest to the ovum lose their tails
(c) cells of corona radiata trap all the sperms except one
(d) only two sperms nearest the ovum penetrate zona pellucida. (Mains 2011)
28. About which day in a normal human menstrual cycle does rapid secretion of LH (popularly called LH surge) normally occurs?
(a) 14th day
(b) 20th day
(c) 5th day
(d) 11th day (Mains 2011)
29. Sertoli cells are found in
(a) ovaries and secrete progesterone
(b) adrenal cortex and secrete adrenaline
(c) seminiferous tubules and provide nutrition to germ cells
(d) pancreas and secrete cholecystokinin. (Prelims 2010)
30. Vasa efferentia are the ductules leading from
(a) testicular lobules to rete testis
(b) rete testis to vas deferens
(c) vas deferens to epididymis
(d) epididymis to urethra. (Prelims 2010)
31. Seminal plasma in human males is rich in
(a) fructose and calcium
(b) glucose and calcium
(c) DNA and testosterone
(d) ribose and potassium. (Prelims 2010)
32. The first movements of the foetus and appearance of hair on its head are usually observed during which month of pregnancy?
(a) fourth month
(b) fifth month
(c) sixth month
(d) third month. (Prelims 2010)
33. The second maturation division of the mammalian ovum occurs
(a) shortly after ovulation before the ovum makes entry into the Fallopian tube
(b) until after the ovum has been penetrated by a sperm
(c) until the nucleus of the sperm has fused with that of the ovum
(d) in the Graafian follicle following the first maturation division. (Prelims 2010)
34. Which one of the following statements about human sperm is correct?
(a) acrosome has a conical pointed structure used for piercing and penetrating the egg, resulting in fertilisation
(b) the sperm lysins in the acrosome dissolve the egg envelope facilitating fertilisation
(c) acrosome serves as a sensory structure leading the sperm towards the ovum
(d) acrosome serves no particular function. (Prelims 2010)
35. Which one of the following statements about morula in humans is correct?
( a) it has almost equal quantity of cytoplasm as an uncleaved zygote but much more DNA
(b) it has far less cytoplasm as well as less DNA than in an uncleaved zygote
(c) it has more or less equal quantity of cytoplasm and DNA as in uncleaved zygote
(d) it has more cytoplasm and more DNA than an uncleaved zygote. (Prelims 2010)
36. The part of Fallopian tube closest to the ovary is
(d) ampulla. (Prelims 2010)
37. Signals from fully developed foetus and placenta ultimately lead to parturition which requires the release of
(a) estrogen from placenta
(b) oxytocin from maternal pituitary
(c) oxytocin from foetal pituitary
(d) relaxin from placenta (Mains 2010)
38. In human female the blastocyst
(a) forms placenta even before implantation
(b) gets implanted into uterus 3 days after ovulation
(c) gets nutrition from uterine endometrial secretion only after implantation
(d) gets implanted in endometrium by the trophoblast cells (Mains 2010)
39. Secretions from which one of the following are rich in fructose, calcium and some enzymes?
(a) male accessory glands
(d) salivary glands (Mains 2010)
40. Seminal plasma in humans is rich in
(a) fructose and calcium but has no enzymes
(b) glucose and certain enzymes but has no calcium
(c) fructose and certain enzymes but poor in calcium
(d) fructose, calcium and certain enzymes. (Prelims 2009)
41. Which one of the following is the correct matching of the events occurring during menstrual cycle?
(a) proliferative phase : rapid regeneration of myometrium and maturation of Graafian follicle
(b) secretory phase : development of corpus luteum and increased secretion of progesterone
(c) menstruation : breakdown of myometrium and ovum not fertilised
(d) ovulation : LH and FSH attain peak level and sharp fall in the secretion of progesterone (Prelims 2009)
42. Given below is a diagrammatic sketch of a portion of human male reproductive system. Select the correct set of the names of the parts labelled At B, C, D
(a) A-vas deferens, B-seminal vesicle, C-prostate, D-bulbourethral gland
(b) A-vas deferens, B-seminal vesicle, C-bulbourethral gland, D-prostate
(c) A-ureter, B-seminal vesicle, C-prostate, D-bulbourethral gland
(d) A-ureter, B-prostate, C-seminal vesicle, D-bulbourethral gland (Prelims 2009)
43. Foetal ejection reflex in human female is induced by
(a) release of oxytocin from pituitary
(b) fully developed foetus and placenta
(c) differentiation of mammary glands
(d) pressure exerted by amniotic fluid. (Prelims 2009)
44. The correct sequence of spermatogenetic stages leading to the formation of sperms in a mature human testis is
(a) spermatogonia – spermatocyte – spermatid – sperms
(b) spermatid – spermatocyte – spermatogonia – sperms
(c) spermatogonia – spermatid – spermatocyte – sperms
(d) spermatocyte – spermatogonia – spermatid – sperms (Prelims 2009)
45. Which one of the following is the most likely root cause why menstruation is not taking place in regularly cycling human female?
(a) maintenance of the hypertrophical endometrial lining
(b) maintenance of high concentration of sex- hormones in the blood stream
(c) retention of well-developed corpus luteum
(d) fertilisation of the ovum (Prelims 2009)
46. A change in the amount of yolk and its distribution in the egg will affect
(a) pattern of cleavage
(b) number of blastomeres produced
(d) formation of zygote. (Prelims 2009)
47. In humans, at the end of the first meiotic division, the male germ cells differentiate into the
(c) primary spermatocytes
(d) secondary spermatocytes. (Prelims 2008)
48. In human adult females oxytocin
(a) stimulates pituitary to secrete vasopressin
(b) causes strong uterine contractions during parturition
(c) is secreted by anterior pituitary
(d) stimulates growth of mammary glands. (Prelims 2008)
49. Which one of the following statements is incorrect about menstruation?
(a) at menopause in the female, there is especially abrupt increase in gonadotropic hormones
(b) the beginning of the cycle of menstruation is called menarche
(c) during normal menstruation about 40 ml blood is lost
(d) the menstrual fluid can easily clot. (Prelims 2008)
50. Which extraembryonic membrane in humans prevents desiccation of the embryo inside the uterus?
(a) yolk sac
(d) allantosis. (Prelims 2008)
51. Which part of ovary in mammals acts as an endocrine gland after ovulation?
(b) germinal epithelium
(c) vitelline membrane
(d) Graafian follicle. (2007)
52. In the human female, menstruation can be deferred by the administration of
(a) combination of FSH and LH
(b) combination of estrogen and progesterone
(c) FSH only
(d) LH only. (2007)
53. Sertoli cells are regulated by the pituitary hormone known as
(d) prolactin. (2006)
54. Withdrawal of which of the following hormones is the immediate cause of menstruation?
(d) FSH-RH (2006)
55. Grey crescent is the area
(a) at the point of entry of sperm into ovum
(b) just opposite to the site of entry of sperm into ovum
(c) at the animal pole
(d) at the vegetal pole. (2005)
56. If mammalian ovum fails to get fertilized, which one of the following is unlikely?
(a) corpus luteum will disintegrate
(b) progesterone secretion rapidly declines
(c) estrogen secretion further increases
(d) primary follicle starts developing. (2005)
57. Ovulation in the human female normally takes place during the menstrual cycle
(a) at the mid secretory phase
(b) just before the end of the secretory phase
(c) at the beginning of the proliferative phase
(d) at the end of the proliferative phase. (2004)
58. Which of the following hormones is not a secretion product of human placenta?
(a) human chorionic gonadotropin
(d) progesterone. (2004)
59. During embryonic development, the establishment of polarity along anterior/posterior, dorsal/ventral or medial/lateral axis is called
(a) organizer phenomena
(b) axis formation
(d) pattern formation. (2003)
60. What is true for cleavage?
(a) size of embryo increases
(b) size of cells decreases
(c) size of cells increases
(d) size of embryo decreases. (2002)
61. Which set is similar?
(a) corpus luteum – Graafian follicles
(b) sebum – sweat
(c) bundle of His – pace maker
(d) vitamin B7 – Niacin. (2001)
62. Blastopore is the pore of
(d) alimentary canal (2000)
63. The middle piece of the sperm contains
(d) nucleus. (1999)
64. After ovulation Graafian follicle regresses into
(a) corpus artesia
(b) corpus callosum
(c) corpus luteum
(d) corpus albicans. (1999)
65. Fertilizin is a chemical substance produced from
(a) polar bodies
(b) middle piece of sperm
(c) mature eggs
(d) acrosome. (1997)
66. In human beings, the eggs are
(d) macrolecithal. (1997)
67. In the fertile human female, approximately on which day of the menstrual cycle does ovulation take place?
(a) day 14
(b) day 18
(d) day 8. (1997)
68. The mammalian corpus luteum produces
(a) luteotrophic hormone
(b) luteinizing hormone
(d) progesterone. (1995)
69. In an egg, the type of cleavage is determined by
(a) the amount and distribution of yolk
(b) the number of egg membranes
(c) the shape and size of the sperm
(d) the size and location of the nucleus. (1995)
70. What is true about cleavage in the fertilized egg in humans?
(a) it starts while the egg is in fallopian tube
(b) it starts when the egg reaches utems
(c) it is meroblastic
(d) it is identical to the normal mitosis. (1994)
71. The extra embryonic membranes of the mammalian embryo are derived from
(b) inner cell mass
(c) formative cells
(d) follicle cells. (1994)
72. In the 28 day human ovarian cycle, the ovulation takes place typically on
(a) day 14 of the cycle
(b) day 28 of the cycle
(c) day 1 of the cycle
(d) day 5 of the cycle. (1994)
73. Coelom derived from blastocoel is known as
(d) enterocoelom. (1994)
74. Extrusion of second polar body from egg nucleus occurs
(a) after entry of sperm before completion of fertilization
(b) after completion of fertilization
(c) before entry of sperm
(d) without any relation of sperm entry. (1993)
75. Termination of gastrulation is indicated by
(a) obliteration of blastocoel
(b) obliteration of archenteron
(c) closure of blastopore
(d) closure of neural tube. (1993)
76. In telolecithal egg the yolk is found
(a) all over the egg
(b) on one side
(c) both the sides
(d) centre. (1993)
77. Acrosome reaction in sperm is triggered by
(b) release of lysin
(c) influx of Na+
(d) release of fertilizin. (1993)
78. Male hormone is produced in the testis by cells of
(d) leydig. (1993)
79. Meroblastic cleavage is a division which is
(d) spiral. (1992)
80. Eye lens is formed from
(d) ectoderm and mesoderm. (1992)
81. Blastopore is
(a) opening of neural tube
(b) opening of gastrocoel
(c) future anterior end of embryo
(d) found in blastula. (1992)
82. Fertilizins are emitted by
(a) immature eggs
(b) mature eggs
(d) polar bodies. (1991)
83. During cleavage, what is true about cells?
(a) nucleocytoplasmic ratio remains unchanged
(b) size does not increase
(c) there is less consumption of oxygen
(d) the division is like meiosis. (1991)
84. Freshly released human egg has
(a) one Y-chromosome
(b) one X-chromosome
(c) two X-chromosome
(d) one X-chromosome and one Y-chromosome (1991)
85. Location and secretion of Leydig’s cells are
(d) pancreas-glucagon. (1991)
86. Middle piece of mammalian sperm possesses
(a) mitochondria and centriole
(b) mitochondria only
(c) centriole only
(d) nucleus and mitochondria. (1991)
87. Gonads develop from embryonic
(d) both mesoderm and endoderm. (1990)
88. How many sperms are formed from a secondary spermatocyte?
(d) 1. (1990)
89. Cells become variable in morphology and function in different regions of the embryo. The process is
(d) rearrangement. (1989)
90. Human eggs are
(d) macrolecithal. (1989)
91. Egg is liberated from ovary in
(a) secondary oocyte stage
(b) primary oocyte stage
(c) oogonial stage
(d) mature ovum stage. (1989)
1. (d) :
In human beings, ovum is released from the ovary in the secondary oocyte stage. The maturation of secondary oocyte is completed in the mother’s oviduct (Fallopian tube) usually after the sperm has entered the secondary oocyte for fertilisation. Entry of the sperm restarts the cell cycle breaking down MPF J (M-phase promoting factor) and turning on APC i (Anaphase promoting complex). Completion of meiosis II converts the secondary oocyte into a fertilised ovum (egg) or zygote (and also a second polar body).
In human females, ovulation is the release of secondary oocyte from the ovary at about 14th day of the menstrual cycle. Both LFI and FSFI attain a peak level during this period. Rapid secretion of LH induces rupturing of fully developed Graafian follicle and thereby release of ovum. LH surge is actually responsible for ovulation.
Ectopic pregnancy is a complication of pregnancy in which implantation of embryo takes place at site other than uterus. Signs and symptoms include abdominal pain and vaginal bleeding. Most ectopic pregnancies (90%) occur in the Fallopian tube, which are known as tubal pregnancies.
Spermatogonia are diploid cells which mature into primary spermatocytes (2n) by growth. They then produce two haploid secondary spermatocytes by meiosis I. Each secondary spermatocyte (n) completes the meiosis II and produces two spermatids (n). Each spermatid (n) develops into a spermatozoon or sperm (n) Similarly, in females, oogonia are the diploid cells from which through meiosis, polar bodies (n) and single ovum (n) are produced.
The secretions of the female genital tract remove coating substances deposited on the surface of the sperms particularly those on the acrosome. Thus, the receptor sites on the acrosome are exposed and sperm becomes active to penetrate the egg. This phenomenon of sperm activation in mammals is known as capacitation.
7. (c) :
Hysterectomy is the surgical removal of uterus. It may also involve removal of the cervix,
ovaries, Fallopian tubes and other surrounding structures.
8. (b) :
Process of parturition is induced by both nervous system and hormones secreted by the endocrine glands of the mother. The signals for child birth (parturition) originate from the fully developed foetus and placenta which induce mild uterine contractions called foetal ejection reflex. This causes quick release of oxytocin from the maternal posterior lobe of pituitary gland which induces labour pains. Prostoglandins, progesterone and estrogen also play a role. Prolactin is the hormone which induces lactation and has no role in parturition.
Urethra is the urinary duct which originates from the neck of urinary bladder and opens to the exterior at the tip of penis in males. It is a common pathway for passage of urine and semen.
Corpus luteum secretes steroid hormones progesterone and estrogen, to make utems suitable for implantation (in case fertilisation occurs) and it’s maintenance (mainly endometrium).
11. (c) :
The trophoblastic cells secrete human chorionic gonadotropin hormone which has properties similar to those of lutenizing hormone (LH) of the pituitary gland. It takes over the job of pituitary LH during pregnancy. The hCG maintains the corpus luteum and stimulates it to secrete progesterone. The latter maintains the endometrium of the utems and causes it to grow throughout pregnancy. This also prevents menstruation. Progesterone also causes increased secretion of mucus in the cervix of the utems that forms a protective plug during pregnancy.
Spermatogenesis is the process of formation of haploid spermatozoa (sperms) from diploid spermatogonia inside the testes of the male. At sexual maturity, the undifferentiated primordial germ cells divide several times by mitosis to produce a large number of spermatogonia or sperm mother cells. Each spermatogonium actively grows to a larger primary spermatocyte by obtaining nourishment from the nursing cells. The phenomenon of formation of primary spermatocytes from spermatogonia, is called spermatocytogenesis. Each primary spermatocyte undergoes two successive divisions, called maturation divisions. The first maturation division is reductional or meiotic. Hence, the primary spermatocyte divides into two haploid daughter cells called secondary spermatocytes. Both secondary spermatocytes now undergo second maturation division which is an ordinary mitotic division to form four haploid spermatids, by each primary spermatocyte. The transformation of spermatids into spermatozoa is called spermiogenesis or spermateleosis or differentiation phase.
Parturition is induced by a complex neuroendocrine mechanism. The signals for parturition j 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 lead to expulsion of the baby out of the uterus through the birth canal.
14. (c) :
The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium. Such as endometrium is necessary for implantation of the fertilized ovum and other events of pregnancy. In the absence of fertilization, the corpus luteum degenerates. This causes disintegration of the i endometrium leading to menstruation. The menstrual flow results due to breakdown of endometrial lining of the uterus and its blood vessels which forms liquid that comes out through vagina.
15. (a) :
The zona granulosa and theca cells of Graafian follicle remaining in the ovary after ovulation and some surrounding capillaries and connective tissue evolve into the corpus luteum (a temporary endocrine gland). The corpus luteum produces progesterone and, in the event of fertilization, provides the required progesterone until the placenta is formed. In the absence of fertilization, the life span of the corpus luteum is 14 days. It then degenerates into a corpus albicans, which is mainly a scar tissue.
16. (b) :
Establishment of sex through differential development in an individual at an early stage of life is called sex determination. It is determined at the time of fertilization and is also called as syngametic sex determination.
The female is homomorphic (isomorphic) possessing two similar sex chromosomes, XX and the male is heteromorphic possessing one X chromosome similar to that of female and one shorter and morphologically different Y chromosome. The female is said to be homogametic (produces similar eggs) and the male heterogametic (produces two types of sperms i.e., X or Y). Sex is determined at the time of fertilization by the kind of sperm (X or Y) that fuses with the ovum (X).
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 muscles 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 i.e., parturition.
Sperms remain viable for 48 hours to 72 hours.
The act of expelling the full term young one from the mother’s uterus at the end of gestation period is called parturition. Parturition is induced by signals from both the fully developed foetus and the placenta. It induces mild uterine contractions called foetal ejection reflex.
20. (d) :
During pregnancy, placenta aljso acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (hCG), human placental estrogen, progesterone, etc. The hCG stimulates and maintains the corpus luteum to secrete progesterone.
Interstitial cells or Leydig cells are the cells interspersed between the seminiferous tubules of the testis. They secrete androgens in response to stimulation by luteinizing hormone from the anterior pituitary gland.
After fertilization, zygote undergoes rapid mitotic divisions, called cleavage, which is characterized by absence of growth of daughter cells. This leads to the conversion of single celled zygote into a multicellular structure called blastocyst or blastula. Implantation or embedding of zygote into endometrium of uterus occurs in blastocyst stage. The various stages in the journey of a fertilized egg from fertilization in the Fallopian tube to the implantation site in the uterus is illustrated in the given figure.
Blastocyst comes in contact with the endometrium in the region of embryonal knob or embryonic disc. It adheres to the same. -The surface cells of trophoblast secrete lytic enzymes which cause corrosion of endometrial lining. They also give rise to finger-like outgrowths called chorionic villi. Chorionic villi and uterine tissue become interdigitated. Villi not only help in fixation but also absorption of nourishment.
After ovulation which occurs in the middle of menstrual cycle, empty Graafian follicle continues growth under the influence of LH. The follicular cells are converted into lutein cells by deposition of yellowish lipid inclusions. The phenomenon is called luteinization. The ruptured Graafian follicle is now called corpus luteum. It secretes hormones, mainly progesterone and small quantity of estrogen. Both LH and progesterone help in further growth and thickening of endometrium. The major change is that the endometrial glands become secretory. The uterine wall becomes ready for nourishing and anchoring blastocyst if fertilization takes place. Hence, this phase of menstrual cycle is called luteal or secretory phase. The phase lasts for about 13 days i.e., 15-28 days of 28 days menstrual cycle.
24. (a) :
The male sex accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens. The seminiferous tubules of the testis open into the vasa efferentia through rete testis. The vasa efferentia leave the testis and open into epididymis located along the posterior surface of each testis So if vasa efferentia gets blocked, the gametes will not be transported from testes to epididymis.
The testes are situated outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes (2-2.5°C lower than the normal internal body temperature) necessary for spermatogenesis.
26. (b) :
The oviducts (Fallopian tubes), uterus and vagina constitute the female accessory ducts. Each Fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the utems, the part closer to the ovary is the funnel-shaped infundibulum. The edges of the infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum after ovulation. The uterus is single and it is also called womb, open into vagina through a narrow cervix. So, III is infundibulum, IV is fimbriae and V is cervix.
27. (a) :
The process of fusion of a sperm with an ovum is called fertilization. During fertilization, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms. Thus, it ensures that only one sperm can fertilize an ovum. The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. In contact with the surface of egg covering, the acrosome releases its contained hydrolytic enzymes, also called sperm lysins. It is known as acrosomal reaction. Acrosome reaction results in dissolving of corona cells and degeneration of zona pellucida which helps in sperm penetration.
Both LH and FSH attain a peak^level in the middle of menstrual cycle (about 14th day). Rapid secretion of LH leading to its maximum level during the mid-cycle called LH surge induces rupture of Graafian follicle and thereby the release of ovum (ovulation).
29. (c) :
Sertoli cells (named after Italian histologist Enrico Sertoli) are found in the walls of the seminiferous tubules of the testis. Compared with the germ cells they appear large and pale. They anchor and probably
nourish the developing germ cells, especially the spermatids, which become partly embedded within them.
30. (b) :
The seminiferous tubules are closed at one end but on the other side they join to a network the rete testis from where fine ciliated ductules, the vasa efferentia arise. Cilia help in conducting sperms. The rete testis is a network of tubules conducting sperm from the seminiferous tubules of the testis to the vasa efferentia.
31. (a) :
Semen or seminal fluid or seminal plasma is the fluid ejaculated from the penis at sexual climax. Each ejaculate may contain 300 – 500 million spermatozoa suspended in a fluid secreted by the prostate gland and seminal vesicles with a small contribution from Cowper’s glands. It is rich in fructose, calcium and certain enzymes. It provides a fluid medium for transport of sperms, nourishes and activates sperms, lubricates the reproductive tract of female and neutralizes the acidity of the vagina of female to protect the sperms.
32. (b) :
In human beings, after one month of pregnancy, the embryo’s heart is formed. By the end of the second month of pregnancy, the foetus develops limbs and digits. By the end of 12 weeks (first trimester), most of the major organ systems are formed. The first movements of the foetus and appearance of hair on the head are usually observed during the fifth month. By the end of 24 weeks (second trimester), the body is covered with fine hair, eye-lids separate, and eyelashes are formed. By the end of nine months of pregnancy, the foetus is fully developed and is ready for delivery.
33. (b) :
Oogenesis starts with division of oogonia (gamete mother cells) giving rise to primary oocyte which enters into prophase-I of the meiotic divison and get temporarily arrested at this stage. These primary oocyte gets surrounded by primary, secondary and tertiary follicles respectively. The tertiary follicle grow in size and completes its first meiotic divison to give rise to haploid secondary oocyte. This secondary oocyte forms a new membrane called zona pellucida surrounding it. During fertilisation the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. This induces the completion of the meiotic division (2nd divison) of the secondary oocyte. The second meiotic division is also unequal and results in the formation of a second polar body and a haploid ovum (ootid).
34. (b) :
Acrosome is the cap-like structure on the front end of a spermatozoon. It breaks down just before fertilisation (the acrosome reaction), releasing a number of hydrolytic enzymes, also called sperm lysins that assist penetration between the follicle cells that still surround the ovum, thus facilitating fertilisation. Failure of the acrosome reaction is a cause of male infertility.
35. (a) :
A morula is an embryo at an early stage of embryonic development, consisting of cells (called blastomeres) in a solid ball contained within the zona pellucida. The morula is produced by embryonic cleavage, the rapid division of the zygote. The increase in number of cells doesn’t change the size of the original mass. The divisions are rapid because there is no net growth of the embryo-the cell cycle alternates between DNA replication and mitosis. In the absence of growth, the cell number in the embryo increases while the cell size decreases. Thus, it has almost equal quantity of cytoplasm as an uncleaved zygote but much more DNA.
Each Fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus, the part closer to the ovary is the funnel-shaped infundibulum. The edges of the infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum after ovulation. The infundibulum leads to a wider part of the oviduct called ampulla. The last part of the oviduct, isthmus has a narrow lumen and it joins the uterus.
37. (b) :
Refer answer 17.
Implantation in endometrial uterine wall takes place at blastocyst stage of embryonic development. Before implantation, the blastomeres of early blastocyst get arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called inner cell mass. It is the trophoblast layer through which blastocyst gets attached to the endometrium and the inner cell mass gets differentiated as the embryo.
The male accessory glands include paired seminal vesicles, a prostate and paired bulbourethral glands. Secretions of these glands constitute the seminal plasma which is rich in fructose, calcium and certain enzymes. The secretions of bulbourethral glands also helps in the lubrication of the penis.
Refer answer 39.
41. (b) :
Secretory phase is also called as luteal phase. The luteinising hormone or LH is secreted by the anterior lobe of pituitary gland. LH causes ovulation. LH stimulates cells of ovarian follicles to develop corpus luteum. Corpus luteum secretes large amount of progesterone.
43. (b) :
Refer answer 19.
Refer answer 12
High concentration of sex steroids (oestrogen) exerts negative feedback on anterior pituitary, decreasing LH secretion and release thus, lowering LH level in blood. Due to insufficient LH level no ovulation occurs which causes irregular menstruation.
Cleavage is a series of cell divisions by which a single fertilized egg cell is transformed into a multicellular body, the blastula. Characteristically no growth occurs during cleavage, the shape of the embryo is unchanged except for the formation of central cavity (the blastocoel), and the ratio of nuclear material (DNA) to cytoplasm increases. The mode of cleavage is determined by the amount of yolk and its distribution. On this basis cleavage may be holoblastic and meroblastic.
During embryonic development the primordial germ cells migrate to the testis where they become spermatogonia. At puberty the spermatogonia proliferate rapidly by mitosis. Some undergo growth phase to become primary spermatocytes that further undergo through meiotic division I to become secondary spermatocytes. After completion of meiotic division II the secondary spermatocytes produce spermatids which differentiate to form spermatozoa.
48. (b) :
In human adult female oxytocin is a hormone released by the pituitary gland (neurohypophysis), that causes contraction of the uterus during labour and stimulates milk flow from the breasts by causing contraction of muscle fibres in the milk ducts.
49. (d) :
Menstruation is a process which involves discharge of blood (45 – 100ml), serous fluid, cell debris and mucosal fragments from cast off endometrial lining due to reduce titre of both estrogen and progesterone hormone. Blood clotting doesn’t occur due to presence of fibrinolysin.
Amnion is a type of extraembryonic membrane formed by the amniogenic cells inside and
splanchnopleuric extraembryonic mesoderm outside. Amnion surrounds the embryo creating the amniotic cavity that is filled with amniotic fluid. The amniotic fluid serves as a shock absorber for the foetus, regulates foetal body temperature and prevents desiccation.
51. (d) :
The Graafian follicle is fluid-filled capsule that surrounds and protects the developing egg cell inside the ovary during the menstrual cycle. Graafian follicle represents the final stage of follicular development before ovulation. Shortly before ovulation the follicle swells and develops a stigma. At ovulation, the stigma ruptures, releasing the secondary oocyte and corona radiata into the peritoneal cavity to be taken up by the oviduct. The zona granulosa and theca cells remaining in the ovary after ovulation and some surrounding capillaries and connective tissue evolve into the corpus luteum (a temporary endocrine gland) i.e after the egg cell has been released, the follicle remains and is known as a corpus luteum. The corpus luteum produces progesterone and, in the event of fertilization, provides the required progesterone until the placenta is formed. The corpus luteum also produces some estrogen.
52. (b) :
Menstruation is the term given to the periodic discharge of blood, tissue, fluid and mucus from the reproductive organs of sexually matured females. The flow usually lasts from 3-6 days each month and is caused by a sudden reduction in the hormones estrogen and progesterone.
Two sex hormones play a role in the control of the menstrual cycle: estradiol and progesterone.
(i) Estrogen peaks twice, during follicular growth and during the luteal phase.
(ii) Progesterone remains virtually absent prior to ovulation, but becomes critical in the luteal phase and during pregnancy. Many tests for ovulation check for the presence of progesterone.
After ovulation the coipus luteum — whigh develops from the burst follicle and remains in the ovary — secretes both estradiol and progesterone. Only if pregnancy occurs do hormones appear in order to suspend the menstrual cycle, while production of estradiol and progesterone continues.
53. (b) :
Sertoli cells are present in the germinal epithelium of the seminiferous tubules. These cells nourish the developing sperms. These cells differentiate spermatogonia into sperms. They are under the influence of FSH released by anterior pituitary gland.
54. (a) :
The menstmal cycle consists of three phases; proliferative phase, secretory phase and menstrual phase. During menstrual phase the production of LH is considerably reduced. The withdrawal of this hormone causes degeneration of the corpus luteum and, therefore, progesterone production is reduced. The endometrium degenerates and breaks down. Thus menstruation begins.
55. (b) :
Grey crescent is the area just opposite to the site of entry of sperm into ovum. It marks the future dorsal side of the embryo.
If the mammalian ovum fails to fertilize choices, (a) and (b) are obvious. Since corpus luteum declines so progesterone also decreases rapidly (progesterone ! is essential for maintenance of pregnancy). Also estrogen continues to cause growth of the endometrium which ultimately becomes thick enough to break down and cause menstruation. Hence choice (c) is incorrect as estrogen secretion does not decrease further. Primary follicles continue developing irrespective of ovulatory condition.
57. (d) :
Ovulation (the release of secondary oocyte from the graafian follicle) takes place at the end of proliferative phase of menstrual cycle. During this phase, the follicle stimulating hormone (FSH) secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete oestrogen. Oestrogen stimulates the proliferation of the endometrium of the uterine wall. The endometrium becomes thicker by rapid cell multiplication and this is accompanied by an increase of uterine glands and blood vessels. This phase ends when the ovarian follicle ruptures and ovulation occurs and at the same time the production of oestrogen stops.
58. (b) :
The outer surface of the chorion in humans develops a number of finger like projections, known as chorionic villi, which grow into the tissue of the uterus. These villi, penetrate the tissues of the uterine wall in which they are embedded, make up the organ known as the placenta, by means of which the developing embryo obtains nutrients and oxygen and gets rid of carbon dioxide and metabolic wastes. Placenta also secretes hormones such as oestrogens, progesterone and human chorionic gonadotropin (HCG). Prolactin is secreted by anterior pituitary gland which stimulates
mammary gland development during pregnancy and lactation after child birth.
59. (a) :
During embryonic development, the establishment of polarity along anterior/posterior, dorsal/ventral or medial/lateral axis is called organizer phenomenon. The organizer is the part of an embryo consisting of undifferentiated cells that follow a specific course of development by identifying the polarity of particular region.
During cleavage, the zygote divides repeatedly to convert the large cytoplasmic mass into a large number of small blastomeres. It involves cell division without growth in size because cells continue to be retained within the zona pellucida. However, cell size decreases during cleavage.
61. (a) :
A mature ovarian follicle is called Graafian follicle. It contains follicular cells, an antmm, and an oocyte. After ovulation, the empty graafian follicle shows deposition of leutin and forms corpus luteum that ultimately degenerates.
Archenteron is known as the primitive gut that forms during gastrulation in the developing blastula. It develops into the digestive tract of an animal. The open end of the archenteron is called blastopore.
The sperm consists of head, neck, middle piece and tail. The middle piece of human sperm contains the mitochondria coiled around the axial filament called mitochondrial spiral. They provide energy for the movement of the sperm.
64. (c) :
After ovulation many of the follicular cells remain in the collapsed Graafian follicle on the surface of the ovary. The antrum (cavity) of the collapsed follicle fills with a partially clotted fluid. The follicular cells enlarge and fill with a yellow pigment, lutein. Such a follicle is called a corpus luteum – literally, yellow body.
Egg (ovum) secretes a chemical named fertilizin (composed of glycoprotein = monosaccharides + amino acids). Sperm has on its surface a protein substance called antifertilizin (composed of acidic amino acids). The fertilizin of an egg interacts with the antifertilizin of a sperm of the same species. This interaction makes the sperms stick to the egg surface. The adhesion of sperm to the egg of the same species through chemical recognition is known as agglutination.
66. (b) :
In human beings, the eggs are alecithal i.e. they do not contain yolk. Mesolecithal eggs contain moderate amount of yolk e.g., frog. Microlecithal eggs contain a little amount of yolk e.g., Amphioxus. Macrolecithal eggs contain large amount of yolk e.g. birds.
67. (a) :
Ovulation is the releasing of egg by ruptured graafian follicle. The wall of graafian follicle is ruptured by sudden increase in the level of luteinising hormone. The length of menstruation cycle is 28 days (average) from the start of one menstruation period to the start of the next. At about 14th day of the cycle, the distended follicle ruptures and the ovum is extruded into the fallopian tube.
Progesterone is secreted by the corpus luteum of the ovary. It stimulates further development of the uterine epithelium and mammary glands. It is also required for the formation of the placenta and for the maintenance of pregnancy. Luteotrophic hormone and luteinizing hormone are secreted by the anterior lobe of pituitary gland. Estrogen is secreted by the cells of the graafian follicles.
69. (a) :
The amount of yolk and how it is distributed determines the type of cleavage. On this basis cleavage is of two types:
(a) Holoblastic – where the segmentation line passes through the entire egg. It occurs in alecithal (without yolk), microlecithal (with very little amount of yolk) and mesolecithal (little amount of yolk) egg.
(b) Meroblastic – where segmentation line does not pass through the egg and remained confined to a part of the egg. It occurs in megalecithal (large amount of yolk) egg.
Cleavage is a series of rapid mitotic divisions of the zygote which convert the single celled zygote into a multicellular structure called blastula (blastocyst).
About thirty hours after fertilization, the newly formed zygote divides into two cells, the blastomeres, in the upper portion of the Fallopian tube. This is the first cleavage. The next division occurs within forty hours after fertilization. The third division occurs about three days after fertilization. During these early cleavages, the young embryo is slowly moving down the fallopian tube towards the uterus. At the end of fourth day, the embryo reaches the uterus. It has thirty two cells.
71. (a) :
Trophoblast is the layer of cells encircling the blastocoel and the inner cell mass. The latter gives rise to the embryo. The cells of the trophoblast form the placenta and foetal membrane.
72. (a) :
Refer answer 67.
73. (a) :
Roundworms have a body cavity called pseudocoelom consisting of a fluid-filled space between the body wall and digestive tract. Pseudocoelom is derived from the blastocoel of the embryo rather than from a secondary cavity within the embryonic mesoderm (which results in a true body cavity or coelom). The internal organs of pseudocoelomate animals are actually found free within the fluid-filled body cavity as there is no layer of mesodermal epithelium lining the cavity and surrounding the organs.
74. (a) :
The entry of sperm stimulates the secondary oocyte to resume and complete the suspended meiosis II. This produces a haploid mature ovum and a second polar body. The second polar body immediately degenerates and sperm tail as well.
75. (a) :
Gastrulation is the process through which the presumptive areas of organ specific rudiments present on the surface of blastula move to their specific positions where these occur in the adult’. Gastrulation results in setting apart of the three primary germinal layers i.e., the ectoderm, mesoderm and endoderm from single layer of cells, the blastoderm, and in the formation of primordial gut or archenteron. Example in Amphioxus, blastula is ball¬like with a large blastocoel surrounded by a single layer of columnar cells. At the onset of gastrulation, the blastoderm at the vegetal pole becomes flat. It gradually bends inwards till the embryo assumes the appearance of a double-walled cup. The cavity formed by invagination is called archenteron or primitive gut. Its opening is called blastopore and the embryo at this stage is gastrula.
As a result of invagination, the presumptive endoderm, mesoderm and notochord are shifted from the surface to the interior of the embryo. The blastocoel is gradually obliterated till the two layers come in contact. By the completion of gastrulation, the lateral horns of mesodermal crescent converge and come to lie on either side of the presumptive notochord.
76. (b) :
Eggs with abundant yolk concentrated in one hemisphere of the egg are termed telolecithal. This occurs in many invertebrates and in all vertebrates lower than marsupial mammals.
77. (c) :
The activated spermatozoan on reaching the egg plasma membrane, undeigoes a number of changes in its acrosomal region. All these changes are collectively described under acrosome reaction. Acrosome reaction is calcium-dependent involving massive uptake of calcium and sodium with an efflux of hydrogen generating high pH and osmotic pressure, producing negative surface charge, and partial or total release of the acrosomal enzymes. Calcium influx may activate phospholipase resulting in accumulation of unsaturated fatty acids and fusiogenic lysophos-pholipids contributing to acrosome reaction.
79. (b) :
Depending mostly on the amount of yolk in the egg, the cleavage can be holoblastic (total or entire cleavage) or meroblastic (partial cleavage). In the presence of a large amount of yolk in the fertilized egg cell, the cell can undergo partial or meroblastic cleavage. Two major types of meroblastic cleavages are discoidal e.g. birds and superficial e.g. arthropods.
Ectoderm, mesoderm and endoderm are the three germ layers that give rise to the specific tissues, organs and organ-systems. Ectoderm gives rise to conjunctiva, cornea, lens of eye, muscles of iris, vitreous humour, retina, lacrimal gland along with other parts of the body.
Blastopore is the opening by which the cavity of the gastrula (gastrocoel), communicates with the exterior. It is formed as a result of invagination of endoderm during embryonic development. During maturation of some animals it evolves into the anus or the mouth; in others it is covered over and contributes to the canal joining the primitive gut with the cavity of the neural tube.
82. (b) :
Mature egg (ovum) secretes a chemical named fertilizin (composed of glycoprotein = monosaccharides + amino acids). Sperm has on its surface a protein substance called antifertilizin (composed of acidic amino acids). The fertilizin of an egg interacts with the antifertilizin of a sperm of the same species. This interaction makes the sperms stick to the egg surface.
83. (b) :
The term cleavage refers to a series of rapid mitotic divisions of the zygote following fertilization, forming a many-celled blastula. Interphase in cleavage divisions is short and does not involve growth so that the resulting blastomeres become smaller in size as their number increases. Thus, the size of the cells (blastomeres) does not increase during cleavage.
84. (b) :
The egg released is haploid (has only one X-chromosome and 22 autosomes) as it is formed due to meiotic division of diploid primary oocyte having XX chromosome and 44 autosomes.
85. (c) :
In between the seminiferous tubules in the connective tissue of testes, there are present small groups of rounded interstitial or Leydig’s cells which secrete androgens (e.g., testosterone), i.e, male sex hormones.
The middle piece of human sperm contains the mitochondria coiled around the axial filament called mitochondrial spiral. They provide energy for the movement of the sperm. At the end of the middle piece there is a ring centriole (annulus) with unknown functions.
Ectoderm, mesoderm and endoderm are the three germ layers that give rise to specific tissues, organs and organ systems. Gonads, muscles, dermis, kidneys etc. develop from mesoderm. Ectoderm produces epidermis, glands, nervous system etc. Pancreas, lining of urinary bladder etc develop from endoderm.
Refer answer 12.
89. (a) :
Differentiation are the changes from simple to more complex forms undergone by developing tissues and organs so that they become specialized for particular functions. Differentiation occurs during embryonic development and regeneration.
Eggs are of 4 types regarding the amount of yolk present in them:
(i) Alecithal egg : Almost free of yolk e.g. man.
(ii) Microlecithal egg : Very small amount of yolk e.g. Branchiostoma.
(iii) Mesolecithal egg : Moderate amount of yolk e.g., Frog’s egg
(iv) Macrolecithal egg : Large amount of yolk e.g. reptiles, birds and egg-laying mammals^.
91. (a) :
In humans, ovum is released from the ovary in the secondary oocyte stage. The wall of the ovary gets ruptured to release the oocyte. In humans ovulation occurs about 14 days before the onset of the next menstruation. Ovulation is induced by LH.