Gametogenesis Questions in English

(B) In the process of oogenesis,the oogonia (germ mother cells) multiply by mitosis and differentiate into primary oocytes. When these primary oocytes enter meiosis-$I$ (prophase-$I$) and get arrested at that stage,they are referred to as primary oocytes. Therefore,the correct answer is $B$.

(C) In the human female,the process of oogenesis starts during embryonic development. By birth,millions of primary follicles are present in the ovaries. However,a large number of these follicles degenerate during the period from birth to puberty. At the stage of puberty,only about $60,000$ to $80,000$ primary follicles remain in each ovary.

(C) The development of the ovarian follicle involves several stages.
$1$. The primary follicle is surrounded by a few layers of granulosa cells.
$2$. The secondary follicle is characterized by more layers of granulosa cells and a new theca layer.
$3$. The tertiary follicle is identified by the presence of a fluid-filled cavity called the antrum.
$4$. Therefore,the antrum is a characteristic feature of the tertiary follicle.

(C) In the human female,the process of oogenesis begins during embryonic development.
Primary oocytes are arrested in the prophase-$I$ stage of meiosis-$I$.
As the follicle matures,the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division (meiosis-$I$).
This division is unequal and results in the formation of a large haploid secondary oocyte and a tiny first polar body.
Therefore,the transformation of the primary oocyte into a secondary oocyte occurs within the tertiary follicle.

(B) The ploidy of the cells involved in oogenesis is as follows:
$1$. Oogonia: $2n$ (Diploid,formed by mitosis).
$2$. Primary Oocyte: $2n$ (Diploid,arrested in Prophase-$I$).
$3$. Secondary Oocyte: $n$ (Haploid,formed after Meiosis-$I$).
$4$. First Polar Body: $n$ (Haploid,formed after Meiosis-$I$).
$5$. Ovum: $n$ (Haploid,formed after Meiosis-$II$).
$6$. Second Polar Body: $n$ (Haploid,formed after Meiosis-$II$).
Therefore,the sequence is: Ovum $(n)$,Secondary Oocyte $(n)$,First Polar Body $(n)$,Second Polar Body $(n)$,Primary Oocyte $(2n)$,Oogonia $(2n)$.

(B) The $Zona$ $pellucida$ is a thick,non-cellular glycoprotein layer that surrounds the plasma membrane of the oocyte.
During the process of oogenesis,the primary oocyte grows and is surrounded by follicular cells to form the primary follicle.
As the follicle develops into a secondary and then a tertiary follicle,the $Zona$ $pellucida$ is secreted by the oocyte itself.
Specifically,this layer is formed around the oocyte while it is in the stage of the secondary oocyte,as it matures within the tertiary follicle before ovulation.

(A) The process of ovulation is primarily triggered by a surge in the levels of Luteinizing Hormone $(LH)$,known as the $LH$ surge.
This surge occurs in the middle of the menstrual cycle (around the $14^{th}$ day in a $28$-day cycle).
$LH$ acts on the mature Graafian follicle to induce the rupture of the follicle and the release of the secondary oocyte.
Therefore,$LH$ is the hormone responsible for ovulation.

(D) In the process of oogenesis,the oogonia undergo mitosis to form primary oocytes $(P)$.
The primary oocytes then undergo meiosis $I$ to form a secondary oocyte and a first polar body $(Q)$.
Therefore,$P$ represents the primary oocyte and $Q$ represents the secondary oocyte.

(D) After ovulation,the secondary oocyte is released from the Graafian follicle.
The remaining parts of the Graafian follicle undergo structural changes to form a temporary endocrine gland known as the $Corpus \ luteum$.
This gland secretes large amounts of progesterone,which is essential for the maintenance of the endometrium.

(B) The secondary oocyte remains arrested in the metaphase-$II$ stage of meiosis-$II$. The completion of meiosis-$II$ occurs only when a sperm enters the secondary oocyte during the process of fertilization. This division results in the formation of a haploid ovum (ootid) and a second polar body. Therefore,the maturation of the secondary oocyte is completed only after fertilization.

(A) $1$. The ovum is a female gamete produced by meiosis,so it is haploid $(n)$.
$2$. The sperm is a male gamete produced by meiosis,so it is haploid $(n)$.
$3$. The zygote is formed by the fusion of the haploid ovum $(n)$ and the haploid sperm $(n)$ during fertilization,resulting in a diploid $(2n)$ cell.
$4$. Therefore,the ploidy sequence is $n, n, 2n$.

(A) The structure of the human ovum consists of several layers surrounding the oocyte.
Starting from the innermost layer to the outermost layer,the arrangement is as follows:
$1$. Plasma membrane (Oolemma): The innermost boundary of the ovum.
$2$. Zona pellucida: $A$ thick,transparent,non-cellular glycoprotein layer surrounding the plasma membrane.
$3$. Corona radiata: The outermost layer consisting of follicular cells that are attached to the zona pellucida.
Therefore,the correct sequence from inside to outside is: Plasma membrane $\rightarrow$ Zona pellucida $\rightarrow$ Corona radiata.

(C) In humans,each somatic cell contains $46$ chromosomes,which consist of $44$ autosomes and $2$ sex chromosomes. During gametogenesis (meiosis),the chromosome number is halved. Therefore,both sperm and ovum are haploid $(n = 23)$. Each gamete contains $22$ autosomes and $1$ sex chromosome. Thus,they contain both autosomes and sex chromosomes.

(C) Germ cells (gametes) are haploid cells produced through meiosis. In humans,a somatic cell contains $46$ chromosomes,consisting of $44$ autosomes and $2$ sex chromosomes. During gametogenesis,these cells undergo meiosis,resulting in gametes that contain half the number of chromosomes. Therefore,a germ cell contains $22$ autosomes and $1$ sex chromosome. Thus,germ cells contain both autosomes and sex chromosomes.

(C) In the process of spermatogenesis,one primary spermatocyte undergoes meiosis-$I$ to form two secondary spermatocytes.
Each secondary spermatocyte then undergoes meiosis-$II$ to form two spermatids.
Thus,one secondary spermatocyte produces two spermatozoa.
To form $400\,million$ spermatozoa,the number of secondary spermatocytes required is calculated as:
$\text{Number of secondary spermatocytes} = \frac{\text{Total spermatozoa}}{2} = \frac{400\,million}{2} = 200\,million$.

(D) The correct answer is option $(D)$.
According to the hormonal control of spermatogenesis:
$(A)$ represents $FSH$ (Follicle Stimulating Hormone),which acts on Sertoli cells.
$(B)$ represents Leydig cells,which are stimulated by $LH$ to secrete androgens.
$(C)$ represents Sertoli cells,which are stimulated by $FSH$ to secrete factors that help in the process of spermiogenesis.
$(D)$ represents Spermiogenesis,which is the process of transformation of spermatids into spermatozoa.

(A) The structure of a human sperm consists of a head,neck,middle piece,and tail.
$1$. The head contains the haploid nucleus,which carries the genetic material $(A-IV)$.
$2$. The middle piece contains numerous mitochondria,which produce energy for the movement of the tail $(B-III)$.
$3$. The acrosome is a cap-like structure present on the head,which contains enzymes (hyaluronidase) that help in the fertilization of the ovum $(C-I)$.
$4$. The tail facilitates the motility of the sperm $(D-II)$.
Therefore,the correct matching is $A-IV, B-III, C-I, D-II$.

(B) After ovulation,the ruptured Graafian follicle transforms into a temporary endocrine structure known as the $Corpus \ luteum$.
This structure secretes large amounts of $progesterone$,which is essential for the maintenance of the endometrium for potential implantation of the embryo.
If fertilization does not occur,the $Corpus \ luteum$ degenerates into a scar-like tissue called $Corpus \ albicans$.

(D) The sperm consists of a head,neck,middle piece,and tail.
The middle piece contains numerous mitochondria,which are known as the powerhouse of the cell.
These mitochondria produce $ATP$ (Adenosine Triphosphate) through aerobic respiration.
This $ATP$ provides the necessary energy for the movement of the tail,which facilitates the motility of the sperm to reach the ovum for fertilization.

(D) To determine the ploidy of the given structures:
$1$. Spermatid: Haploid $(n)$
$2$. Secondary oocyte: Haploid $(n)$
$3$. Primary spermatocyte: Diploid $(2n)$
$4$. Ovum: Haploid $(n)$
$5$. Sperm: Haploid $(n)$
$6$. Oogonia: Diploid $(2n)$
$7$. Spermatogonia: Diploid $(2n)$
$8$. Polar body: Haploid $(n)$
The haploid structures are: Spermatid,secondary oocyte,ovum,sperm,and polar body.
Counting these,we get a total of $5$ haploid structures.

(B) Statement-$I$ is correct because during the development of the ovary,primary oocytes get surrounded by layers of granulosa cells and are termed as primary follicles.
Statement-$II$ is incorrect because at puberty,the number of primary follicles remaining in each ovary is $60,000-80,000$. The statement incorrectly mentions 'secondary follicles' instead of 'primary follicles'.
Therefore,Statement-$I$ is correct and Statement-$II$ is incorrect.

(D) During fetal development,millions of oogonia are formed within each fetal ovary. No more oogonia are formed or added after birth.
These oogonia start division and enter into prophase-$I$ of the meiotic division and get temporarily arrested at that stage,called primary oocytes.
Each primary oocyte gets surrounded by a layer of granulosa cells and is called the primary follicle.
$A$ large number of these follicles degenerate during the phase from birth to puberty.
Therefore,at puberty,only $60,000 - 80,000$ primary follicles are left in each ovary.

(B) During fetal development,millions of oogonia are formed within each fetal ovary. No more oogonia are formed or added after birth. These oogonia start division and enter into prophase-$I$ of the meiotic division and get temporarily arrested at that stage,called primary oocytes. Each primary oocyte then gets surrounded by layers of granulosa cells and is called the primary follicle. $A$ large number of these follicles degenerate during the phase from birth to puberty. Therefore,at puberty,only $60,000-80,000$ primary follicles are left in each ovary.

(A) $1$. $Spermatogenesis$ is the process of formation of sperms from spermatogonia.
$2$. $Spermiogenesis$ is the transformation of spermatids into spermatozoa.
$3$. After $spermiogenesis$,the sperm heads become embedded in the $Sertoli$ cells to derive nutrition.
$4$. Finally,the release of sperms from the seminiferous tubules is known as $spermiation$.

(A) The growing ovarian follicles are responsible for the production and secretion of the hormone $Estrogen$.
$Estrogen$ is a steroid hormone that plays a crucial role in the development and maintenance of female secondary sexual characteristics and the regulation of the menstrual cycle.
$Progesterone$ is primarily secreted by the $Corpus$ $Luteum$ after ovulation.
$Androgens$ and $Testosterone$ are primarily male sex hormones,although they are present in small amounts in females.

(D) The 'Antrum' is a fluid-filled cavity that characterizes the development of the ovarian follicle.
During the process of folliculogenesis,the primary follicle develops into a secondary follicle and then into a tertiary follicle.
The tertiary follicle is distinguished by the presence of a fluid-filled cavity called the 'Antrum'.
This cavity is formed by the accumulation of follicular fluid secreted by the granulosa cells.
Therefore,the correct option is $D$.

(D) In gametogenesis,diploid cells contain two sets of chromosomes $(2n)$.
$A$. The second polar body is haploid $(n)$ as it is formed after the completion of meiosis $II$.
$B$. The first polar body is haploid $(n)$ as it is formed after the completion of meiosis $I$.
$C$. Spermatids are haploid $(n)$ cells formed after the completion of meiosis $II$ in spermatogenesis.
$D$. Oogonia are the primary germ cells in the ovary that undergo mitosis to multiply and are diploid $(2n)$.
Therefore,the correct option is $D$.

(C) In the process of oogenesis and ovarian cycle,the development of follicles follows a specific sequence:
$1$. Primordial follicles develop into primary follicles.
$2$. Primary follicles develop into secondary follicles.
$3$. Secondary follicles develop into tertiary follicles,characterized by a fluid-filled cavity called the antrum.
$4$. The tertiary follicle further matures into the Graafian follicle (mature follicle).
$5$. Upon ovulation,the secondary oocyte is released,and the remaining parts of the Graafian follicle transform into a temporary endocrine structure called the corpus luteum.
Therefore,in a standard diagrammatic representation,$C$ typically represents the mature (Graafian) follicle,and $E$ represents the corpus luteum formed after ovulation.

(D) The $Zona$ $pellucida$ is a thick, transparent, and acellular glycoprotein layer that surrounds the plasma membrane of the oocyte.
It is secreted by the oocyte itself and plays a crucial role in sperm binding and the prevention of polyspermy.
In contrast, the $Theca$ $Interna$, $Granulosa$, and $Corona$ $radiata$ are all cellular layers composed of follicular cells.

(C) The transformation of non-motile spermatids into mature,motile spermatozoa (sperm) is known as $Spermiogenesis$.
$Spermatogenesis$ is the entire process of formation of sperm from spermatogonia.
$Oogenesis$ is the process of formation of a mature female gamete.
$Insemination$ is the process of transfer of sperm into the female genital tract.

(B) In human spermatogenesis,the process involves several stages:
$1$. Spermatogonia are diploid $(2n = 46)$ cells.
$2$. Primary spermatocytes are also diploid $(2n = 46)$.
$3$. After the first meiotic division (meiosis-$I$),the primary spermatocyte divides to form two haploid $(n = 23)$ secondary spermatocytes.
$4$. Sertoli cells and Leydig cells are somatic cells of the testis and are diploid $(2n = 46)$.
Therefore,the secondary spermatocyte is the only cell among the options that contains $23$ chromosomes.

(D) $Statement-I$ is incorrect because the gonadotropin releasing hormone $(GnRH)$ is secreted by the hypothalamus, not the pituitary gland.
$Statement-II$ is correct because $GnRH$ acts on the anterior pituitary gland to stimulate the secretion of gonadotropins, specifically follicle stimulating hormone $(FSH)$ and luteinizing hormone $(LH)$, which subsequently induce gametogenesis.
Therefore, $Statement-I$ is incorrect and $Statement-II$ is correct.

(C) In the structure of a sperm cell,the 'Nebenkern' refers to the mitochondrial sheath,which is formed by the aggregation of mitochondria in the middle piece of the sperm. Therefore,'$X$' = Mitochondria.
The acrosome is a cap-like structure present at the anterior part of the sperm head. It is derived from the Golgi apparatus during the process of spermiogenesis. Therefore,'$Y$' = Golgi body.
Thus,the correct analogy is Nebenkern: Mitochondria :: Acrosome: Golgi body.

(C) During fetal development,millions of oogonia are formed in each ovary.
By birth,these oogonia transform into primary oocytes and are surrounded by layers of granulosa cells to form primordial follicles.
Most of these follicles undergo degeneration during childhood.
As a result,at the time of puberty,only about $60,000$ to $80,000$ primary follicles remain in each ovary,which is often approximated as $40,000$ to $60,000$ in standard textbooks.

(C) In human females,the process of oogenesis involves the development of the ovum. The primary oocyte completes its first meiotic division to form a secondary oocyte and a first polar body. The secondary oocyte then begins the second meiotic division but gets arrested at the metaphase-$II$ stage. This division is only completed when a sperm enters the secondary oocyte during fertilization. Therefore,the final completion of oogenesis occurs upon the entry of sperm into the ooplasm.

(A) Spermatogenesis occurs in three distinct phases: the multiplication phase,the growth phase,and the maturation phase.
$1$. Multiplication phase: Spermatogonia $(2n)$ undergo repeated mitotic divisions to increase their number.
$2$. Growth phase: Spermatogonia accumulate nutrients and increase in size to become primary spermatocytes $(2n)$.
$3$. Maturation phase: Primary spermatocytes undergo meiosis to form secondary spermatocytes $(n)$ and subsequently spermatids $(n)$.
Therefore,the growth phase results in the formation of primary spermatocytes.

(C) The correct matching is as follows:
$1$. $A$. Head contains $Q$. Acrosome, which $Z$. secretes penetrating enzymes (hyaluronidase) to facilitate fertilization.
$2$. $B$. Neck contains $P$. Centrioles, which $X$. help in the formation of the synkaryon spindle during the first cleavage of the zygote.
$3$. $C$. Middle piece contains $R$. Nebenkern (mitochondria), which $Y$. provides energy for sperm movement.
$4$. $D$. Tail contains $S$. Axial filament, which $W$. facilitates whiplash movement in the female reproductive tract.
Therefore, the correct sequence is $A-Q-Z, B-P-X, C-R-Y, D-S-W$.

(B) In the process of oogenesis,the oogonia $(2n)$ undergo mitosis to form primary oocytes $(2n)$.
The primary oocyte then undergoes meiosis $I$ (a reductional division) to form a large secondary oocyte $(n)$ and a small first polar body $(n)$.
In the provided diagram,'$A$' represents the cell that undergoes meiosis $I$ to produce the secondary oocyte and the first polar body.
Therefore,'$A$' is the primary oocyte,which is diploid $(2n)$.

(D) The provided diagram represents the structure of a human ovum (unfertilized egg).
$1$. The outermost layer consists of follicular cells,which form the 'corona radiata'. In the diagram,'$X$' points to these cells.
$2$. The layer immediately surrounding the plasma membrane of the ovum is the 'zona pellucida'. In the diagram,'$Y$' points to this thick,transparent layer.
$3$. Therefore,'$X$' represents the corona radiata and '$Y$' represents the zona pellucida.

(A) In human females,the process of oogenesis is initiated during the embryonic development stage.
Millions of gamete mother cells (oogonia) are formed within each fetal ovary.
No more oogonia are formed or added after birth.
Therefore,the formation of oogonia is completed during the embryonic stage.

(B) The rapid secretion of $LH$ leading to its maximum level during the mid-cycle is called the $LH$ surge.
This $LH$ surge induces the rupture of the Graafian follicle and thereby the release of the ovum (secondary oocyte) from the ovary.
This process is known as ovulation.
Therefore,a sudden rise in the level of $LH$ stimulates ovulation.

(A) In the human female reproductive cycle,ovulation typically occurs around the $14^{th}$ day of a $28$-day menstrual cycle.
During this process,the Graafian follicle ruptures to release the female gamete.
At the time of ovulation,the female gamete is arrested in the metaphase stage of Meiosis-$II$ and is technically referred to as a secondary oocyte.
The secondary oocyte completes Meiosis-$II$ only upon the entry of a sperm during fertilization.

(C) During spermatogenesis, the $Primary$ spermatocyte undergoes the first meiotic division (meiosis-$I$), which is a reductional division.
This process results in the formation of two haploid cells known as $Secondary$ spermatocytes.
These cells contain only $n$ number of chromosomes compared to the diploid $(2n)$ $Primary$ spermatocyte.

(C) Oogenesis is the process of formation of a mature female gamete.
In humans,the secondary oocyte completes the second meiotic division only after the entry of a sperm.
This division is unequal and results in the formation of a large haploid ovum (ootid) and a tiny second polar body.
The formation of the second polar body marks the completion or termination of the process of oogenesis.

(A) In the human ovary,the development of follicles is stimulated by $FSH$ (Follicle Stimulating Hormone).
As the follicles mature,the follicular cells (specifically the granulosa cells) produce and secrete the hormone estrogen.
$Sertoli$ cells are found in the testes,not the ovary.
$Corona$ $radiata$ cells are protective layers surrounding the oocyte,and the primary oocyte is the germ cell itself,not the endocrine tissue producing estrogen.
Therefore,the correct answer is follicular cells.

(D) The primordial germ cells (PGCs) are the precursors of gametes. In humans, these cells originate from the endoderm of the $yolk sac$ during early embryonic development. From the $yolk sac$, these cells migrate to the developing gonads (ovaries or testes) to differentiate into $oogonia$ or $spermatogonia$, respectively.

(A) The sperm tail consists of an axial filament,which is a microtubular structure. This axial filament arises from the distal centriole of the sperm cell. The proximal centriole is located near the nucleus and is involved in the first cleavage of the zygote after fertilization,while the distal centriole gives rise to the flagellum or tail of the sperm.

(B) Spermiogenesis is the process of transformation of spermatids into spermatozoa (sperm).
During this process,the following changes occur:
$1$. The nucleus condenses and becomes smaller.
$2$. The Golgi apparatus forms the acrosome.
$3$. Mitochondria arrange themselves to form the mitochondrial sheath (middle piece).
$4$. The cytoplasm is reduced.
However,the formation of proximal and distal centrioles occurs during the earlier stages of spermatogenesis (specifically during the division of spermatogonia or spermatocytes),not during the transformation of spermatids into spermatozoa.
Therefore,the correct answer is $B$.

(D) During the process of oogenesis,the primary oocyte undergoes meiosis-$I$ to form a large haploid secondary oocyte and a small first polar body.
This secondary oocyte then proceeds to meiosis-$II$,but it gets arrested at the metaphase-$II$ stage.
Ovulation is the process in which the Graafian follicle ruptures to release this secondary oocyte into the fallopian tube.
Therefore,the correct answer is the secondary oocyte.

(B) $FSH$ stands for Follicle Stimulating Hormone.
It is secreted by the anterior pituitary gland.
In females,$FSH$ stimulates the growth and development of ovarian follicles (Graafian follicles).
It also stimulates the secretion of estrogens by the ovarian follicles.
Therefore,the growth of the Graafian follicle is initiated by $FSH$.