47 Questions with Answers and Explanations on “Reproduction & Embryonic Development” for Biology Students.
1. Cells become variable in morphology and function in different regions of the embryo. The process is
(a) differentiation
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(b) metamorphosis
(c) organisation
(d) rearrangement
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Answer and Explanation:
1. (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.
2. Human eggs are
(a) alecithal
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(b) microlecithal
(c) mesolecithal
(d) macrolecithal
Answer and Explanation:
2. (a): 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 eg. Frog’s egg
(iv) Macrolecithal egg: Large amount of yolk eg, reptiles, birds and egg-laying mammals.
3. Egg is liberated from ovary in
(a) secondary oocyte stage
(b) primary oocyte stage
(c) oogonial stage
(d) mature ovum stage.
Answer and Explanation:
3. (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.
4. Gonads develop from embryonic
(a) ectoderm
(b) endoderm
(c) mesoderm
(d) both mesoderm and endoderm.
Answer and Explanation:
4. (c): 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.
5. How many sperms are formed from a secondary spermatocyte?
(a) 4
(b) 8
(c) 2
(d) 1.
Answer and Explanation:
5. (c): At sexual maturity, the undifferentiated primordial germ cells divide several times by mitosis to produce a large number of spermatogonia. Each spermatogonium actively grows to a larger primary spermatocyte. 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.
Thus each secondary spermatocyte gives rise to two spermatids that undergo transformation to form two sperms. Overall, both secondary spermatocytes give rise to four sperms.
6. Fertilizins are emitted by
(a) immature eggs
(b) mature eggs
(c) sperms
(d) polar bodies.
Answer and Explanation:
6. (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.
7. 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.
Answer and Explanation:
7. (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.
8. 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
Answer and Explanation:
8. (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.
9. Location and secretion of Leydig’s cells are
(a) liver-cholesterol
(b) ovary-estrogen
(c) testis-testosterone
(d) pancreas-glucagon.
Answer and Explanation:
9. (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.
10. Middle piece of mammalian sperm possesses
(a) mitochondria and centriole
(b) mitochondria only
(c) centriole only
(d) nucleus and mitochondria.
Answer and Explanation:
10. (a): 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.
11. Meroblastic cleavage is a division which is
(a) horizontal
(b) partial/parietal
(c) total
(d) spiral.
Answer and Explanation:
11. (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.
12. Eye lens is formed from
(a) ectoderm
(b) mesoderm
(c) endoderm
(d) ectoderm and mesoderm.
Answer and Explanation:
12. (a): 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.
13. Blastopore is
(a) opening of neural tube
(b) opening of gastrocoel
(c) future anterior end of embryo
(d) found in blastula.
Answer and Explanation:
13. (b): 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.
14. 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.
Answer and Explanation:
14. (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 I sperm tail as well.
15. Termination of gastrulation is indicated by
(a) obliteration of blastocoel
(b) obliteration of archenteron
(c) closure of blastopore
(d) closure of neural tube.
Answer and Explanation:
15. (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 a part 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.
16. In telolecithal egg the yolk is found
(a) all over the egg
(b) on one side
(c) both the sides
(d) centre.
Answer and Explanation:
16. (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.
17. Acrosome reaction in sperm is triggered by
(a) capacitation
(b) release of lysin
(c) influx of Na+
(d) release of fertilizin.
Answer and Explanation:
17 (c): The activated spermatozoan on reaching the egg plasma membrane undergoes 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 lysophospholipids contributing to acrosome reaction.
18. Amount of yolk and its distribution are changed in the egg. Which one is affected?
(a) pattern of cleavage
(b) formation of zygote
(c) number of blastomeres
(d) fertilization.
Answer and Explanation:
18. (a): Based on the amount and pattern of distribution of yolk in the zygote, cleavage is of two types: holoblastic and meroblastic. Holoblastic cleavage divides the zygote and blastomeres completely into daughter cells. In meroblastic cleavage the divisions are confined to the animal pole or peripheral region of egg. The yolk remains undivided.
19. Male hormone is produced in the testis by cells of
(a) Sertoli
(b) epithelial
(c) spermatocytes
(d) leydig.
Answer and Explanation:
19. (d): Refer answer 9.
20. 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 uterus
(c) it is meroblastic
(d) it is identical to the normal mitosis.
Answer and Explanation:
20. (a): 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.
21. The extra embryonic membranes of the mammalian embryo are derived from
(a) trophoblast
(b) inner cell mass
(c) formative cells
(d) follicle cells.
Answer and Explanation:
21. (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.
22. 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.
Answer and Explanation:
22. (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.
23. Coelom derived from blastocoel is known as
(a) pseudocoelom
(b) schizocoel
(c) haemocoel
(d) enterocoelom.
Answer and Explanation:
23. (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.
24. Which of the following statements is correct with reference to a test tube baby?
(a) fertilization of the egg is effected outside the body; the fertilized egg is then placed in the womb of the mother where the gestation is completed
(b) fertilization of the egg is effected in the female genital tract. It is then taken out and grown in a large test tube
(c) a prematurely born baby is reared in an incubator
(d) fertilization of the egg and growth of the embryo are affected in a large test tube.
Answer and Explanation:
24. (a): By in vitro fertilization, the ovum is fertilized with sperm outside the body of a woman, providing the ovum with the same environmental conditions as it would have got inside the uterus. The zygote is grown inside a culture and when embryo is formed, it is then implanted into uterus where it develops into foetus and then into a child. This is called test tube baby.
25. The mammalian corpus luteum produces
(a) luteotrophic hormone
(b) luteinizing hormone
(c) estrogen
(d) progesterone.
Answer and Explanation:
25. (d): 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.
26. 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.
Answer and Explanation:
26. (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.
27. The test tube baby means
(a) fertilization and development both in uterus
(b) fertilization in vitro and then transplantation in uterus
(c) a baby grown in test tube
(d) fertilized and developed embryo in test tube.
Answer and Explanation:
27. (b): Refer answer 24.
28. Foetal sex can be determined by examining cells from the amniotic fluid by looking for
(a) chiasmata
(b) kinetochore
(c) barr bodies
(d) autosomes.
Answer and Explanation:
28. (c): Barr body is a structure consisting of a condensed X chromosome that is found in nondividing nuclei of female mammals. Amniotic fluid contains foetal skin cells, that are stained to determine the presence of sex chromatin (barr body). The presence of barr body indicates that the developing foetus is female with two X-chromosome.
29. Fertilizin is a chemical substance produced from
(a) polar bodies
(b) middle piece of sperm
(c) mature eggs
(d) acrosome.
Answer and Explanation:
29. (c): 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 fertilizing 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.
30. In human beings, the eggs are
(a) mesolecitlial
(b) alecithal
(c) microlecithal
(d) macrolecithal
Answer and Explanation:
30. (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.
31. In the fertile human female, approximately on which day of the menstrual cycle does ovulation take place?
(a) day 14
(b) day 18
(c) day 1
(d) day 8.
Answer and Explanation:
31. (a): Refer answer 22.
32. The middle piece of the sperm contains
(a) proteins
(b) mitochondria
(c) centriole
(d) nucleus.
Answer and Explanation:
32. (b): 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.
33. After ovulation Graafian follicle regresses into
(a) corpus artesia
(b) corpus callosum
(c) corpus luteum
(d) corpus albicans.
Answer and Explanation:
33. (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.
34. Blastopore is the pore of
(a) archenteron
(b) blastocoel
(c) coelom
(d) alimentary canal
Answer and Explanation:
34. (a): 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.
35. Which set is similar?
(a) corpus luteum – graafian follicles
(b) sebum – sweat
(c) bundle of His – pace maker
(d) vitamin B7 – Niacin.
Answer and Explanation:
35. (a): A mature ovarian follicle is called Graafian follicle. It contains follicular cells, an antrum, and an oocyte. After ovulation, the empty graffian follicle shows deposition of leutin and forms corpus luteum that ultimately degenerates.
36. 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.
Answer and Explanation:
36. (b): During cleavage, the zygote divides repeatedly to convert the large cytoplasmic mas- into a Iarge 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.
37. Test tube baby means a baby born when
(a) it is developed in a test tube
(b) it is developed through tissue culture method
(c) the ovum is fertilized externally and thereafter implanted in the uterus
(d) it develops from a non-fertilized uterus
Answer and Explanation:
37. (c): By in vitro fertilization, the ovum is fertilized with sperm outside the body of a woman, providing the ovum with the same environmental conditions as it would have got inside the uterus. The zygote is grown inside a culture and when embryo is formed, it is then implanted into uterus where it develops into foetus and then into a child. This is called test tube baby.
Methodology involves the following steps:
• Removal of unfertilised ovum from reproductive tract of a female.
Ovum is kept under aseptic conditions.
• Fusion of sperm and ovum in a culture medium, outside the female body to form the zygote.
• Zygote is stimulated to develop in vitro upto 32-celled stage.
• Developing embryo is implanted on the endometrium of the uterus at 32-celled stage. So the pregnancy in the woman starts and further the development of the child continues in the womb till it is born.
38. During embryonic development, the establishment of polarity along anterior/posterior, dorsal/ventral or medial/lateral axis is called
(a) organizer phenomena
(b) axis formation
(c) anamorphosis
(d) pattern formation
Answer and Explanation:
38. (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.
39. 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.
Answer and Explanation:
39. (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.
40. Which of the following hormones is not a secretion product of human placenta?
(a) human chorionic gonadotropin
(b) prolactin
(c) estrogen
(d) progesterone.
Answer and Explanation:
40. (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.
41. In oogamy, fertilization involves
(a) a small non-motile female gamete and a large motile male gamete
(b) a large non-motile female gamete and a small motile male gamete
(c) a large non-motile female gamete and a small non-motile male gamete
(d) a large motile female gamete and a small non- motile male gemete.
Answer and Explanation:
41. (b): Oogamy is the sexual reproduction involving the formation and subsequent fusion of a large, usually stationary, female gamete and a small motile male gamete. The female gamete may contain nourishment for the development of the embryo, which is often retained and protected by the parent organism.
42. 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.
Answer and Explanation:
42. (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.
43. 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.
Answer and Explanation:
43. (c): 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 doesnot decrease further. Primary follicles continue developing irrespective of ovulatory condition.
44. Sertoli cells are regulated by the pituitary hormone known as
(a) LH
(b) FSH
(c) GH
(d) prolactin
Answer and Explanation:
44. (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.
45. Withdrawal of which of the following hormones is the immediate cause of menstruation?
(a) progesterone
(b) estrogen
(c) FSH
(d) FSH-RH
Answer and Explanation:
45. (a): The menstrual 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.
46. Which part of ovary in mammals acts as an endocrine gland after ovulation?
(a) stroma
(b) germinal epithelium
(c) vitelline membrane
(d) Graafian follicle.
Answer and Explanation:
46. (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 ovul ation. Shortly before ovulation the follicle swells and develops a stigma. At ovulation, the stigma ruptures, releaising 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.
47. 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.
Answer and Explanation:
47. (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. Estrogen peaks twice, during follicular growth and during the luteal phase.
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 corpus luteum — which 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.
