Gametogenesis Questions in English

(A) In the process of spermatogenesis,a single primary spermatocyte undergoes meiosis $I$ to form two secondary spermatocytes.
Each secondary spermatocyte then undergoes meiosis $II$ to form two spermatids.
Thus,one primary spermatocyte results in the formation of four spermatids.
These four spermatids eventually differentiate into four functional spermatozoa (sperm cells).

(B) In the process of oogenesis,one primary oocyte undergoes meiosis to produce only one functional ovum and two or three polar bodies.
Since the question states that $10$ primary oocytes are involved,each primary oocyte will yield exactly one ovum.
Therefore,$10$ primary oocytes will produce $10 \times 1 = 10$ ova.
Thus,the correct answer is $10$.

(B) The acrosome is a cap-like structure present on the anterior portion of the sperm head. It is derived from the Golgi apparatus. The acrosome and its covering membrane are collectively referred to as the $Galea \text{ capitis}$.

(D) sperm differs from an ovum in several ways:
$1$. Motility: Sperm are motile due to the presence of a tail,whereas ova are non-motile.
$2$. Food storage: Sperm do not store food,while the ovum contains a significant amount of cytoplasm and yolk (in many species) to support early development.
$3$. Number: Sperm are produced in very large numbers,whereas usually only one ovum is released per menstrual cycle in humans.
Therefore,all the given options are correct.

(B) $Sertoli$ cells,also known as nurse cells,are located within the seminiferous tubules of the testes.
Their primary function is to provide structural and nutritional support to the developing germ cells (spermatids) during the process of spermatogenesis.
They also form the blood-testis barrier and secrete factors that regulate spermatogenesis.

(C) The process of formation and deposition of yolk in the developing oocyte is known as $Vitellogenesis$.
$Lipogenesis$ refers to the synthesis of fatty acids and triglycerides.
$Glycogenesis$ is the process of glycogen synthesis from glucose.
$Oogenesis$ is the overall process of formation of a mature female gamete (ovum).

(B) In non-primate mammals,the reproductive cycle is known as the estrous cycle.
Ovulation,the release of the secondary oocyte from the ovary,typically occurs during the estrus phase (also known as the 'heat' period).
This is the period when the female is sexually receptive to the male,facilitating fertilization.

(B) The acrosome is a cap-like structure present on the anterior part of the sperm head. It is derived from the Golgi apparatus during the process of spermiogenesis. The acrosome contains hydrolytic enzymes that help in the penetration of the ovum during fertilization.

(A) After the release of the secondary oocyte during ovulation,the remaining parts of the Graafian follicle undergo luteinization.
This process involves the transformation of the ruptured follicle into a temporary endocrine gland known as the $Corpus \ luteum$.
This structure secretes large amounts of progesterone,which is essential for the maintenance of the endometrium during pregnancy.

(A) Vitamin $A$ is essential for the maintenance of epithelial tissues and is involved in the process of spermatogenesis. Vitamin $E$ (tocopherol) is known as the anti-sterility vitamin because it is crucial for the normal functioning of the reproductive system and the production of healthy gametes (sperm and ova). Therefore,$Vit. \,A$ and $E$ are considered essential for gametogenesis.

(B) The functional maturation of sperm,which includes the acquisition of motility and the ability to fertilize an egg,occurs in the $Epididymis$.
After being produced in the $Seminiferous$ $tubules$ of the $Testes$,immature sperm move to the $Epididymis$.
In the $Epididymis$,they undergo physiological changes that allow them to become motile and capable of fertilization.

(D) The Graafian follicle is a mature,fluid-filled follicle in the ovary of mammals within which an oocyte develops before ovulation. It is a characteristic structure of the mammalian female reproductive system.

(D) In $Centrolecithal$ eggs,the yolk is concentrated in the center of the egg,and the cytoplasm is restricted to a thin peripheral layer surrounding the yolk. This type of egg is commonly found in insects (e.g.,$Drosophila$).

(A) During the development of the ovarian follicle, the surrounding stromal cells differentiate into two layers known as theca layers.
The $Theca \text{ } externa$ is the outer, fibrous layer of the follicle, which provides structural support.
The $Theca \text{ } interna$ is the inner, vascularized layer that produces hormones.
Therefore, the correct answer is $Theca \text{ } externa$.

(B) After ovulation,the Graafian follicle ruptures to release the secondary oocyte. The remaining follicular tissue collapses and fills with blood,forming a temporary structure known as the $Corpus \ haemorrhagicum$. Subsequently,this structure undergoes luteinization to become the $Corpus \ luteum$,which secretes progesterone. If fertilization does not occur,it eventually degenerates into the $Corpus \ albicans$. $Corpus \ callosum$ is a structure in the brain,not the ovary.

(C) During spermatogenesis,a diploid primary spermatocyte undergoes meiosis $I$ to form two haploid secondary spermatocytes.
Each secondary spermatocyte then undergoes meiosis $II$ to form two haploid spermatids.
Thus,one primary spermatocyte results in the formation of four spermatids,which subsequently differentiate into four functional spermatozoa.

(A) Hyaluronidase is a hydrolytic enzyme found in the acrosome of the sperm.
It is commonly referred to as 'sperm lysin'.
During fertilization,the acrosome releases this enzyme to digest the hyaluronic acid present in the corona radiata of the ovum,thereby facilitating the entry of the sperm into the ovum.

(B) Secondary sexual characteristics are the physical features that distinguish the two sexes of a species but are not directly part of the reproductive system. These characteristics first appear during $Puberty$ due to the surge in sex hormones (testosterone in males and estrogen/progesterone in females). During this phase, the body undergoes significant developmental changes such as the growth of facial hair in males, breast development in females, and voice changes.

(A) During oogenesis,the primary oocyte undergoes the first meiotic division $(Meiosis-I)$ to form two unequal haploid cells. The larger cell is the secondary oocyte,and the smaller cell is the first polar body. The second meiotic division $(Meiosis-II)$ occurs only if fertilization takes place,resulting in the formation of the second polar body.

(A) Spermiogenesis is the process of transformation of non-motile spermatids into mature,motile spermatozoa (sperm).
$1$. Spermatogonia $(2n)$ undergo mitosis to form primary spermatocytes.
$2$. Primary spermatocytes $(2n)$ undergo meiosis-$I$ to form secondary spermatocytes $(n)$.
$3$. Secondary spermatocytes $(n)$ undergo meiosis-$II$ to form spermatids $(n)$.
$4$. Spermatids $(n)$ undergo spermiogenesis to differentiate into spermatozoa $(n)$.
Therefore,the correct option is $A$.

(D) In the process of spermatogenesis,the $Spermatogonia$ $(2n)$ undergo mitotic divisions to form $Primary$ $spermatocytes$ $(2n)$.
These $Primary$ $spermatocytes$ then undergo the first meiotic division $(Meiosis-I)$,which is a reductional division.
As a result of $Meiosis-I$,each $Primary$ $spermatocyte$ gives rise to two equal haploid cells called $Secondary$ $spermatocytes$ $(n)$.
Therefore,after the completion of the first meiotic division,the cells formed are $Secondary$ $spermatocytes$.

(B) The seminiferous tubules are the structural and functional units of the testes.
Inside these tubules,there are two main types of cells: male germ cells (spermatogonia) and Sertoli cells.
Sertoli cells are also known as 'nurse cells' or 'sustentacular cells'.
Their primary function is to provide nutrition and support to the developing germ cells (spermatids) during the process of spermatogenesis.

(D) The stored food in an animal ovum is known as yolk.
It provides the necessary nutrients for the development of the embryo.
In human eggs,the amount of yolk is very small,which is referred to as alecithal or microlecithal.

(D) The $Corpus$ $luteum$ is a temporary endocrine structure in female mammals that is involved in the production of relatively high levels of progesterone and moderate levels of estradiol and inhibin $A$. It is formed from the ruptured follicle after ovulation within the $Ovary$.

(A) Spermatogenesis involves the transformation of spermatids into mature spermatozoa.
This process is known as $Spermiogenesis$.
During this stage,the spermatids undergo significant morphological changes,including the condensation of the nucleus,the formation of the acrosome,the development of the flagellum,and the reduction of cytoplasm,resulting in a mature sperm structure.

(B) The formation of a polar body is a characteristic feature of oogenesis,which is the process of egg formation in females.
During oogenesis,the primary oocyte undergoes meiosis $I$ to produce a large secondary oocyte and a small first polar body.
Subsequently,the secondary oocyte undergoes meiosis $II$ to produce a large ovum (ootid) and a second polar body.
Therefore,polar bodies are formed during the process of oocyte formation.

(C) The $Antrum$ is a fluid-filled cavity that characterizes the mature ovarian follicle,known as the $Graafian$ $follicle$.
During the process of oogenesis,as the primary follicle develops into a secondary and then a tertiary follicle,a fluid-filled space called the $Antrum$ appears.
This cavity is filled with follicular fluid and is a hallmark feature of the $Graafian$ $follicle$ before ovulation occurs.

(A) In mammals,the testes are located outside the abdominal cavity within a pouch called the scrotum.
This is because the process of spermatogenesis (the formation of sperm) requires a temperature that is $2-2.5^{\circ}C$ lower than the normal internal body temperature.
The scrotum provides this cooler environment,which is essential for the viability and proper development of sperm.

(A) Ovulation is the process of releasing a secondary oocyte from the Graafian follicle.
This process is triggered by a rapid surge in the levels of Luteinizing Hormone $(LH)$,commonly known as the $LH$ surge.
This surge occurs mid-cycle,typically around the $14^{th}$ day of a $28$-day menstrual cycle.
Therefore,$LH$ is the primary hormone responsible for inducing ovulation.

(D) Microlecithal eggs are eggs that contain a very small amount of yolk.
In mammals,specifically the infraclass $Eutheria$ (placental mammals),the eggs are microlecithal and alecithal because the developing embryo receives nutrition directly from the mother through the placenta.
Therefore,the correct answer is $Eutheria$.

(B) Spermatogenesis is the process of formation of sperms in the testes.
It is primarily regulated by hormones secreted by the anterior pituitary gland.
$FSH$ (Follicle Stimulating Hormone) acts on the Sertoli cells and stimulates the secretion of some factors which help in the process of spermiogenesis.
$LH$ (Luteinizing Hormone) acts on the Leydig cells and stimulates the synthesis and secretion of androgens,which in turn stimulate the process of spermatogenesis.
Therefore,$FSH$ is directly involved in the regulation and support of spermatogenesis.

(C) After ovulation,the ruptured Graafian follicle transforms into a temporary endocrine structure known as the $Corpus \ luteum$.
This gland secretes large amounts of $Progesterone$,which is essential for maintaining the endometrium of the uterus for implantation of the fertilized ovum.
If fertilization does not occur,the $Corpus \ luteum$ degenerates into a scar tissue called $Corpus \ albicans$.

(C) The $FSH$ (Follicle Stimulating Hormone) is secreted by the anterior pituitary gland.
It acts on the Sertoli cells present in the seminiferous tubules of the testes.
$FSH$ stimulates the Sertoli cells to secrete factors that help in the process of spermiogenesis (the transformation of spermatids into spermatozoa).
Therefore,the correct option is $C$.

(D) Estrogen is primarily secreted by the growing ovarian follicles,specifically the cells of the Graafian follicle.
While the corpus luteum primarily secretes progesterone,the developing Graafian follicle is the main source of estrogen during the follicular phase of the menstrual cycle.

(B) In mammals,the process of ovulation is regulated by the gonadotropic hormones secreted by the anterior pituitary gland.
$FSH$ (Follicle Stimulating Hormone) promotes the growth and maturation of the ovarian follicles.
$LH$ (Luteinizing Hormone) triggers the rupture of the mature Graafian follicle,leading to the release of the secondary oocyte,which is known as ovulation.
Therefore,the correct combination of hormones responsible for this process is $FSH$ and $LH$.

(A) The secretion of estrogen from the ovarian follicles is primarily stimulated by the Follicle Stimulating Hormone $(FSH)$.
$FSH$ acts on the granulosa cells of the ovarian follicles to promote their growth and the production of estrogen.
While $LH$ is responsible for ovulation and the formation of the corpus luteum (which secretes progesterone),$FSH$ is the primary regulator of estrogen synthesis during the follicular phase.

(A) Ovulation is the process of releasing a secondary oocyte from the Graafian follicle in the ovary.
This process is triggered by a rapid surge in the levels of Luteinizing Hormone $(LH)$,commonly known as the '$LH$ surge',which occurs approximately $24-36$ hours before ovulation.
While $FSH$ stimulates the growth of ovarian follicles,$LH$ is specifically responsible for the rupture of the mature Graafian follicle and the subsequent release of the ovum.

(A) Spermatogenesis is regulated by the hormones secreted by the anterior pituitary gland.
$FSH$ (Follicle Stimulating Hormone) acts on the Sertoli cells and stimulates the secretion of some factors which help in the process of spermiogenesis.
$LH$ (Luteinizing Hormone) acts on the Leydig cells and stimulates the synthesis and secretion of androgens,which in turn stimulate the process of spermatogenesis.
Since $FSH$ is directly involved in the maturation and support of the process,it is the primary regulator of spermatogenesis.

(D) The corpus luteum is formed from the remains of the Graafian follicle after ovulation.
It is primarily regulated and maintained by the Luteinizing Hormone $(LH)$ secreted by the anterior pituitary gland.
$LH$ stimulates the corpus luteum to secrete progesterone,which is essential for maintaining the endometrium during pregnancy.

(C) In spermatogenesis, one primary spermatocyte undergoes meiosis to produce $4$ functional spermatozoa.
To find the number of spermatogonia (primary spermatocytes) required to produce $52$ spermatozoa, we divide the total number of spermatozoa by $4$.
Number of spermatogonia = $\frac{52}{4} = 13$.
Therefore, $13$ spermatogonia are required to produce $52$ spermatozoa.

(D) Inhibin is a peptide hormone produced by the granulosa cells of the ovarian follicles in females and by the Sertoli cells (nurse cells) in the testes of males.
Its primary physiological function is to provide negative feedback to the anterior pituitary gland.
Specifically,inhibin selectively inhibits the secretion of $FSH$ (Follicle Stimulating Hormone) without significantly affecting the secretion of $LH$ (Luteinizing Hormone).
Therefore,the statement that it is produced by granulosa cells in the ovary and inhibits the secretion of $FSH$ is correct.

(D) The correct answer is $D$. In human females,the secondary oocyte is released from the ovary during ovulation. The process of meiosis-$II$ remains arrested at the metaphase-$II$ stage. The completion of meiosis-$II$ occurs only when a sperm enters the secondary oocyte during the process of fertilisation. The entry of the sperm triggers the degradation of $MPF$ ($M$-phase promoting factor) and activates the $APC$ ($Anaphase$ promoting complex),allowing the cell to complete the second meiotic division,resulting in the formation of a mature ovum and a second polar body.

(B) The $Zona \ pellucida$ is a thick,transparent,and acellular glycoprotein layer that surrounds the plasma membrane of an oocyte.
It is secreted by both the oocyte and the surrounding follicular cells.
Other layers like the $Granulosa$ cells and $Theca \ interna$ are composed of living cells,while the $Stroma$ refers to the connective tissue framework of the ovary.

(C) The correct answer is $C$.
Ovulation in human females involves the release of the secondary oocyte from the Graafian follicle,typically occurring around the $14^{th}$ day of the menstrual cycle.
This process is triggered by a rapid surge in Luteinizing Hormone $(LH)$ and Follicle Stimulating Hormone $(FSH)$,known as the $LH$ surge.
Before ovulation,the levels of estradiol (estrogen) reach their peak to stimulate the $LH$ surge; therefore,a decrease in estradiol is not associated with the event of ovulation itself,as the surge is dependent on high estrogen levels.

(A) : Spermatogonia are diploid cells $(2n)$ which mature into primary spermatocytes $(2n)$ through growth. They then produce two haploid secondary spermatocytes $(n)$ by meiosis $I$. Each secondary spermatocyte $(n)$ completes meiosis $II$ and produces two spermatids $(n)$. Each spermatid $(n)$ develops into a spermatozoan or sperm $(n)$. Similarly,in females,oogonia are the diploid cells $(2n)$ from which,through meiosis,haploid polar bodies $(n)$ and a single ovum $(n)$ are produced.

(C) : The sperms in the female genital tract are made capable of fertilising the egg by secretions of the female genital tract.
These secretions 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 the sperm becomes active to penetrate the egg.
This phenomenon of sperm activation in mammals is known as capacitation.

(B) The $corpus$ $luteum$ is a temporary endocrine structure formed from the ruptured follicle after ovulation.
Its primary function is to secrete large amounts of $progesterone$, which is essential for maintaining the $endometrium$ of the uterus for potential pregnancy.
It also secretes some amount of $estrogen$.
Therefore, $progesterone$ is the principal hormone produced by the $corpus$ $luteum$.

(B) The correct sequence is $B$.
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,resulting in two haploid daughter cells called secondary spermatocytes.
Both secondary spermatocytes undergo a second maturation division (mitotic) to form four haploid spermatids.
The final transformation of spermatids into functional spermatozoa is called spermiogenesis.

(A) The correct answer is $A$.
Statement $A$ is false because mammalian sperm typically remain viable in the female reproductive tract for $48$ to $72$ hours,not just $24$ hours.
Statement $B$ is true as sperm motility and survival are enhanced in an alkaline environment,which helps them navigate the acidic environment of the vagina.
Statement $C$ is true because motility is a primary indicator of sperm health and viability.
Statement $D$ is true as a high concentration of sperm is necessary to ensure successful fertilization.

(B) The correct answer is $B$. Oogenesis begins with the division of oogonia (gamete mother cells),which give rise to primary oocytes. These primary oocytes enter prophase $I$ of meiosis and are temporarily arrested at this stage. As the follicle matures,the primary oocyte completes its first meiotic division to form a haploid secondary oocyte and a first polar body. The secondary oocyte then begins the second meiotic division but arrests at metaphase $II$. This second meiotic division is only completed after the sperm penetrates the secondary oocyte during fertilization. This process results in the formation of a second polar body and a mature haploid ovum (ootid).