Gametogenesis Questions in English

(B) Germ cells (primary germ cells or spermatogonia/oogonia) are the precursor cells that undergo meiosis to produce gametes. These cells are diploid in nature,meaning they contain two sets of chromosomes,represented as $2n$.

(B) The process of transformation of spermatids into mature spermatozoa is known as $Spermiogenesis$.
After $Spermiogenesis$,sperm heads become embedded in the $Sertoli$ cells and are finally released from the seminiferous tubules by the process called $Spermiation$.
$Spermatogenesis$ is the overall process of formation of sperm from spermatogonia.

(A) The process of spermatogenesis occurs within the seminiferous tubules of the testes.
$1$. The process begins with spermatogonia (diploid germ cells) located at the inner side of the seminiferous tubule.
$2$. These undergo mitosis to increase in number and differentiate into primary spermatocytes.
$3$. Primary spermatocytes undergo meiosis $I$ to form two haploid secondary spermatocytes.
$4$. Secondary spermatocytes undergo meiosis $II$ to form four haploid spermatids.
$5$. Finally,spermatids undergo spermiogenesis to transform into mature spermatozoa (sperm).

(B) During spermatogenesis,the primary spermatocyte $(2n = 46)$ undergoes the first meiotic division (meiosis-$I$) to form two haploid secondary spermatocytes $(n = 23)$.
Since meiosis-$I$ is a reductional division,the chromosome number is halved from the diploid state $(46)$ to the haploid state $(23)$.
Therefore,a secondary spermatocyte contains $23$ chromosomes.

(B) In the process of spermatogenesis,each primary spermatocyte undergoes meiosis-$I$ to form two secondary spermatocytes.
Each secondary spermatocyte then undergoes meiosis-$II$ to produce two spermatids.
Therefore,one secondary spermatocyte produces $2$ spermatids.
Given that there are $200$ secondary spermatocytes,the total number of spermatids produced will be $200 \times 2 = 400$.

(C) The cells responsible for the nourishment of sperm are known as $Sertoli$ cells.
$FSH$ (Follicle Stimulating Hormone) acts on the $Sertoli$ cells and stimulates the secretion of some factors which help in the process of spermiogenesis.
$LH$ acts on the $Leydig$ cells to stimulate the synthesis and secretion of androgens.
Therefore,the correct hormone that acts on the cells responsible for sperm nourishment is $FSH$.

(B) The process of spermiogenesis is regulated by hormones secreted by the anterior pituitary gland.
$1$. The hypothalamus releases Gonadotropin-Releasing Hormone $(GnRH)$.
$2$. $GnRH$ stimulates the anterior pituitary to secrete Luteinizing Hormone $(LH)$ and Follicle-Stimulating Hormone $(FSH)$.
$3$. $LH$ acts on the Leydig cells to stimulate the synthesis and secretion of androgens (testosterone).
$4$. $FSH$ acts on the Sertoli cells and stimulates the secretion of some factors which help in the process of spermiogenesis.

(A) The acrosome is a cap-like structure present at the anterior end of the sperm head.
It is derived from the Golgi apparatus and is filled with hydrolytic enzymes,collectively known as sperm lysins (e.g.,hyaluronidase).
These enzymes are essential for penetrating the egg's protective layers (zona pellucida) during fertilization.

(D) According to the $NCERT$ textbook,for normal fertility,at least $60 \%$ of all sperms must have normal shape and size,and at least $40 \%$ of them must show vigorous motility. Therefore,the correct option is $D$.

(D) The process of oogenesis in females is initiated during the embryonic development stage.
During fetal development,a couple of million gamete mother cells (oogonia) are formed within each fetal ovary.
No more oogonia are formed or added after birth.
These cells start division and enter into prophase-$I$ of the meiotic division and get temporarily arrested at that stage,called primary oocytes.

(C) During oogenesis,the primary oocytes enter the $Prophase-I$ stage of meiosis-$I$ and become temporarily arrested at this stage. This specific arrested stage is known as the 'Dictyate' stage. These primary oocytes are present in the ovary at the time of birth and remain arrested in this stage until the onset of puberty.

(A) During fetal development,millions of oogonia are formed within each fetal ovary. No more oogonia are formed or added after birth.
Each oogonium starts division and enters into prophase-$I$ of the meiotic division and gets 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) In the process of oogenesis,the oogonia undergo mitosis to form primary oocytes. These primary oocytes are arrested at the prophase-$I$ stage of meiosis-$I$. $A$ primary oocyte surrounded by a layer of granulosa cells is called a primary follicle. As the follicle develops into a secondary follicle,it still contains the primary oocyte. The primary oocyte only completes meiosis-$I$ to become a secondary oocyte after the follicle matures into a tertiary follicle and is triggered by the luteinizing hormone $(LH)$ surge.

(D) In the human female reproductive system,the process of oogenesis involves the development of ovarian follicles.
As the follicle matures,it progresses through various stages: primary,secondary,and tertiary follicles.
The mature,fully developed follicle that is ready for ovulation is known as the $Graafian$ follicle.
Therefore,the correct option is $D$.

(B) Ovulation is the process in the human female reproductive cycle where a mature follicle ruptures to release the egg.
During oogenesis,the primary oocyte completes its first meiotic division within the Graafian follicle to form a large haploid secondary oocyte and a tiny first polar body.
The secondary oocyte is the stage that is released from the ovary during ovulation.
It remains arrested in the metaphase stage of meiosis-$II$ until fertilization occurs.

(D) The secondary oocyte released into the fallopian tube is surrounded by two primary layers:
$1$. Inner layer: This is called the $Zona \text{ } pellucida$,which is composed of glycoproteins.
$2$. Outer layer: This is called the $Corona \text{ } radiata$,which is composed of follicular cells.
Therefore,the correct answer is both $A$ and $C$.

(B) The process of oogenesis begins during embryonic development.
Primary oocytes are formed from oogonia through mitosis.
Since oogonia are diploid $(2n)$,the primary oocytes formed from them are also diploid $(2n)$.
Therefore,the ploidy of a primary oocyte is diploid.

(D) In females,oogenesis begins during embryonic development.
Primary oocytes are formed and arrested at the prophase-$I$ stage of meiosis-$I$.
These primary oocytes remain in this arrested state until puberty.
At puberty,the primary oocyte completes meiosis-$I$ to form a large haploid secondary oocyte and a tiny first polar body.
Therefore,the secondary oocyte is formed during puberty.

(B) The process of oogenesis involves the formation of a mature female gamete.
During the first meiotic division (meiosis $I$),the primary oocyte ($46$ chromosomes) undergoes unequal division to form a large secondary oocyte and a small first polar body.
Since meiosis $I$ is a reductional division,the chromosome number is halved.
Therefore,the secondary oocyte contains $23$ chromosomes (haploid state).

(D) 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 maintaining the endometrium for potential implantation of the embryo.

(C) In the human female reproductive system,the process of oogenesis results in the formation of a secondary oocyte. During ovulation,the secondary oocyte is released from the Graafian follicle. If fertilization does not occur,this secondary oocyte (arrested in metaphase $II$) is shed along with the uterine lining during menstruation.

(C) During the process of spermatogenesis,spermatids are transformed into spermatozoa (sperm) by a process called spermiogenesis.
After spermiogenesis,the sperm heads become embedded in the Sertoli cells to receive nourishment before being released into the seminiferous tubules by a process called spermiation.
Therefore,during the differentiation and maturation phase,spermatids and developing spermatozoa are closely associated with Sertoli cells.

(B) Spermatogenesis is the process of formation of spermatozoa from spermatogonia. It consists of three main phases:
$1$. Multiplication phase: Spermatogonia divide by mitosis to increase in number.
$2$. Growth phase: Spermatogonia grow in size by accumulating nutrients to form primary spermatocytes. This is the longest phase of spermatogenesis.
$3$. Maturation phase: Primary spermatocytes undergo meiosis to form secondary spermatocytes and then spermatids.
Spermiogenesis is the transformation of spermatids into spermatozoa,which is a separate process following the maturation phase.

(D) mature sperm consists of four main parts: the head,neck,middle piece,and tail.
$1$. The head contains an elongated haploid nucleus and an anterior cap-like structure called the acrosome.
$2$. The neck contains two centrioles: the proximal centriole and the distal centriole.
$3$. The middle piece contains numerous mitochondria which provide energy for sperm motility.
$4$. The tail facilitates the movement of the sperm.
Therefore,a mature sperm contains a nucleus,acrosome,a pair of centrioles,and a tail.

(A) Spermiogenesis is the process of transformation of spermatids into spermatozoa.
During this process,the Golgi apparatus of the spermatid modifies and condenses to form the acrosome,which is a cap-like structure covering the anterior part of the sperm head.
The acrosome contains hydrolytic enzymes that help in the penetration of the egg during fertilization.

(C) Spermatogenesis is the process of formation of spermatozoa from spermatogonia in the testes.
Vitamin $A$ is essential for the maintenance of the germinal epithelium of the seminiferous tubules.
Vitamin $E$ (tocopherol) is known as the anti-sterility vitamin and is crucial for the normal functioning of the reproductive system and the process of spermatogenesis.
Deficiency of these vitamins can lead to impaired sperm production and infertility.
Therefore,both Vitamin $A$ and Vitamin $E$ are essential for spermatogenesis.

(B) In human females, the process of oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells $(oogonia)$ are formed within each fetal ovary.
No more $oogonia$ are formed or added after birth.
These cells start division and enter into $prophase-I$ of the meiotic division and get temporarily arrested at that stage, called $primary$ $oocytes$.
Therefore, at the time of birth, the ovaries contain a large number of $primary$ $oocytes$.

(C) In human gametogenesis,the ploidy of cells changes during meiosis.
$1$. $Oogonia$ $(2n)$ are diploid cells that undergo mitosis to form primary oocytes $(2n)$.
$2$. $Primary$ $oocytes$ $(2n)$ undergo meiosis $I$ to form a secondary oocyte $(n)$ and a first polar body $(n)$.
$3$. $Primary$ $spermatocytes$ $(2n)$ undergo meiosis $I$ to form secondary spermatocytes $(n)$.
Therefore,the secondary oocyte is a haploid $(n)$ structure.

(B) Yolk is the nutrient-bearing portion of an egg cell. Its primary function is to provide nourishment for the developing embryo. It consists mainly of proteins,lipids,and vitamins stored in the cytoplasm of the egg cell.

(D) The female secondary sex hormone, primarily $Estrogen$, is secreted by the $Theca \, interna$ layer of the Graafian follicle.
$Theca \, interna$ is the inner vascularized layer of the theca folliculi that contains endocrine cells responsible for the synthesis of steroid hormones.
$Zona \, pellucida$ is a glycoprotein layer surrounding the oocyte.
$Corona \, radiata$ consists of follicular cells surrounding the zona pellucida.
$Theca \, externa$ is the outer fibrous layer of the follicle.

(B) In the process of oogenesis,the primary oocyte undergoes meiosis $I$ to form a secondary oocyte and a first polar body.
This secondary oocyte is the stage that is released from the ovary during ovulation.
The secondary oocyte remains arrested in metaphase $II$ until fertilization occurs.
Therefore,the correct form released is the secondary oocyte.

(A) Somatic cells are diploid $(2n)$ in nature. Given that the number of chromosomes in a somatic cell is $42$,it implies $2n = 42$.
The cuboidal epithelial cells (Sertoli cells or germinal epithelium) lining the seminiferous tubules are also somatic cells,which are diploid $(2n)$.
Therefore,the number of chromosomes in these cells will remain $42$.

(B) Spermatogenesis is regulated by the hormones secreted by the hypothalamus and the anterior pituitary gland.
$1$. The hypothalamus secretes Gonadotropin-Releasing Hormone $(GnRH)$.
$2$. $GnRH$ stimulates the anterior pituitary to secrete two gonadotropins: Luteinizing Hormone $(LH)$ and Follicle-Stimulating Hormone $(FSH)$.
$3$. $LH$ acts on the Leydig cells and stimulates the synthesis and secretion of androgens (mainly testosterone).
$4$. $FSH$ acts on the Sertoli cells and stimulates the secretion of some factors which help in the process of spermiogenesis.
Therefore,$FSH$ and $LH$ are the primary regulators of spermatogenesis.

(B) $1$. In oogenesis,one secondary oocyte undergoes meiosis-$II$ to produce one ovum and one polar body. Therefore,$10$ secondary oocytes will produce $10$ ova.
$2$. In spermatogenesis,one secondary spermatocyte undergoes meiosis-$II$ to produce two spermatids,which then differentiate into two spermatozoa. Therefore,to produce $40$ spermatozoa,the number of secondary spermatocytes required is $40 / 2 = 20$.

(D) $Inhibin$ is a glycoprotein hormone produced by the $Sertoli$ cells in the testes of males.
Its primary function is to provide negative feedback to the anterior pituitary gland to inhibit the secretion of $FSH$ ($Follicle$ $Stimulating$ $Hormone$).
This mechanism helps in the regulation of spermatogenesis.

(C) In humans,the secondary oocyte remains arrested at the $Metaphase-II$ stage of meiosis. The completion of meiosis-$II$ is triggered only when a sperm enters the secondary oocyte. Upon the entry of the sperm,the secondary oocyte completes its second meiotic division,resulting in the formation of a large haploid ovum (ootid) and a second polar body. Therefore,the extrusion of the second polar body occurs after the entry of the sperm but before the fusion of the male and female pronuclei (completion of fertilization).

(D) After ovulation,the secondary oocyte (ovum) is released from the Graafian follicle.
It is surrounded by an inner non-cellular layer called the $Zona \ pellucida$.
Outside the $Zona \ pellucida$,there is a layer of follicular cells known as the $Corona \ radiata$.
Therefore,the ovum is surrounded by both $Zona \ pellucida$ and $Corona \ radiata$.

(C) Spermiogenesis is the process of transformation of spermatids into mature spermatozoa (sperms).
During this process,the non-motile,spherical spermatids undergo structural changes to become motile,elongated spermatozoa.
Spermatids are haploid cells formed after the second meiotic division of secondary spermatocytes.
Therefore,the correct cell type that undergoes spermiogenesis is the spermatid.

(D) The sperm consists of a head,neck,middle piece,and tail. The middle piece contains numerous mitochondria,which are arranged in a spiral pattern (often called the Nebenkern). These mitochondria produce energy in the form of $ATP$ required for the movement of the tail,which facilitates sperm motility.

(B) Spermiation is the process by which mature spermatozoa are released from the Sertoli cells into the lumen of the seminiferous tubules.
After the process of spermiogenesis,where spermatids transform into spermatozoa,the heads of the spermatozoa become embedded in the Sertoli cells.
Spermiation marks the final step of spermatogenesis before the sperm move into the epididymis for maturation and storage.

(A) In a normal healthy male,the total sperm count per ejaculation is about $200$ to $300$ million sperm.
Since the average volume of semen per ejaculation is about $2$ to $5 \ ml$,the concentration of sperm in $1 \ ml$ of semen typically ranges from $20$ to $120$ million.
Therefore,the correct range for $1 \ ml$ of semen is $20$ to $120$ million.

(D) The process of transformation of spermatids into mature spermatozoa is known as $Spermiogenesis$.
During this stage,several structural changes occur in the spermatid,including the formation of the acrosome from the Golgi complex,the condensation of the nucleus,and the development of the flagellum.
Therefore,the acrosome is formed during the $Spermiogenesis$ phase.

(C) Primordial Germ Cells (PGCs) are the precursor cells that give rise to gametes (sperm or ova) through the process of gametogenesis.
These cells are diploid in nature,meaning they contain two sets of chromosomes,one inherited from each parent.
Therefore,the ploidy of Primordial Germ Cells is $2n$.

(D) In the ovarian follicle,the $LH$ (Luteinizing Hormone) receptors are specifically located on the cells of the theca interna.
Upon stimulation by $LH$,these cells produce androgens,which are then converted into estrogens by the granulosa cells under the influence of $FSH$ (Follicle Stimulating Hormone).
Therefore,the correct option is $D$.

(D) The options $A$,$B$,and $C$ ($Primary \ spermatocyte$,$Primary \ oocyte$,and $Spermatogonia$) are all diploid $(2n)$ cells involved in the process of gametogenesis.
In contrast,the $First \ polar \ body$ (option $D$) is a haploid $(n)$ cell formed during the process of oogenesis after the completion of meiosis-$I$.

(A) The germinal epithelium of the seminiferous tubules contains cells called $Spermatogonia$ (singular: $Spermatogonium$).
These cells undergo mitotic divisions to increase in number and then differentiate into $Spermatocytes$,which eventually develop into $Spermatozoa$ through the process of spermatogenesis.
Therefore,the cells of the germinal epithelium that give rise to spermatozoa are known as $Spermatogonia$.

(D) Spermatogenesis involves the formation of spermatozoa from spermatogonia.
It consists of two main phases: spermatocytogenesis (meiotic divisions) and spermiogenesis.
Spermiogenesis is the final stage of spermatogenesis where non-motile spermatids are transformed into mature,motile spermatozoa.
During this process,the Golgi apparatus of the spermatid gives rise to the acrosome,which is a cap-like structure containing enzymes essential for fertilization.

(A) In the development of an ovarian follicle, the follicle is surrounded by layers of cells known as theca cells.
These are organized into two layers:
$1$. $Theca \text{ } externa$: This is the outer fibrous layer of the follicle.
$2$. $Theca \text{ } interna$: This is the inner vascularized layer.
Therefore, the fibrous layer is the $Theca \text{ } externa$.

(C) Gametogenesis involves the formation of haploid gametes from diploid germ cells. The process consists of three phases: multiplication,growth,and maturation. The reduction division,also known as $Meiosis-I$,occurs during the first maturation division. During this stage,the diploid primary germ cell (e.g.,primary spermatocyte or primary oocyte) undergoes meiosis to produce two haploid secondary germ cells,thereby reducing the chromosome number by half.

(A) The provided diagram represents a cross-section of a seminiferous tubule.
In this diagram:
- Label $a$ points to the $Spermatogonia$ (immature germ cells located at the periphery of the tubule).
- Label $b$ points to the $Primary \text{ } spermatocytes$.
- Label $c$ points to the $Spermatozoa$ (mature sperm cells near the lumen).
- Label $d$ points to the $Sertoli \text{ } cells$ (supporting cells).
Therefore, label $a$ represents $Spermatogonia$.