Gametogenesis Questions in English

(A) The human sperm was first observed and described by Antonie van Leeuwenhoek in $1677$. He used his self-designed microscope to observe the semen sample and identified the motile cells,which he called 'animalcules'. Therefore,the correct answer is Leeuwenhoek.

(A) Ovulation is the process in the menstrual cycle where a mature ovarian follicle (Graafian follicle) ruptures and releases the secondary oocyte into the fallopian tube. This typically occurs around the $14^{th}$ day of a $28$-day menstrual cycle.

(B) The head of a mature mammalian sperm consists of a haploid nucleus and an acrosome.
The acrosome is a cap-like structure derived from the Golgi apparatus that contains hydrolytic enzymes essential for penetrating the egg during fertilization.
The nucleus contains the condensed genetic material.
Other parts like the centrioles are located in the neck,while the mitochondria are found in the middle piece of the sperm.

(D) Haploid cells contain a single set of chromosomes $(n)$.
$A$. Zygote is formed by the fusion of male and female gametes,making it diploid $(2n)$.
$B$. Amoeba is a unicellular organism that is diploid $(2n)$ in its vegetative state.
$C$. $A$ queen honeybee is a female organism and is diploid $(2n)$.
$D$. Ovum is a female gamete produced through meiosis,which results in a haploid $(n)$ chromosome number.

(C) The process of degeneration and resorption of ovarian follicles and oocytes that do not reach the stage of ovulation is known as follicular atresia. This is a continuous process occurring throughout a female's reproductive life.

(C) The Graafian follicle is the mature ovarian follicle that develops during the menstrual cycle.
It contains a single secondary oocyte (ovum) suspended in the follicular fluid,which is released during ovulation.

(A) In most mammals,ovulation occurs spontaneously due to hormonal changes (the $LH$ surge). However,in certain mammals like rabbits,cats,and camels,ovulation is induced by the act of coitus. This is known as induced ovulation. Therefore,for these specific animals,coitus is required for the reflex action of ovulation.

(C) Capacitation is the physiological maturation process that sperm must undergo in order to be able to penetrate and fertilize an egg.
This process occurs within the female reproductive tract,specifically in the vagina and the uterus,where secretions from the female reproductive tract remove cholesterol and glycoproteins from the sperm's plasma membrane,thereby increasing its motility and membrane fluidity.
Therefore,among the given options,the vagina is the correct site where this process begins.

(B) Oligospermia is a medical condition characterized by a low sperm count in the semen.
In this condition,the concentration of spermatozoa is below the normal threshold,which can lead to male infertility.
Therefore,the correct option is $B$.

(C) During the process of spermiogenesis,the spermatid undergoes significant morphological changes to transform into a functional sperm. One of the key changes is the reduction of cytoplasm. In a mature sperm,the cytoplasm is almost entirely shed,leaving only a very thin layer around the nucleus in the head region. Therefore,it is present in very scarce amounts.

(B) In vertebrates,the process of gametogenesis (spermatogenesis in males and oogenesis in females) is primarily regulated by the gonadotropins secreted by the anterior pituitary gland.
$FSH$ (Follicle Stimulating Hormone) plays a crucial role in stimulating the development of ovarian follicles in females and the production of sperm in males by acting on the Sertoli cells.
$LH$ (Luteinizing Hormone) also works alongside $FSH$ to regulate reproductive functions.
Therefore,$FSH$ is the correct hormone among the given options that directly influences gametogenesis.

(B) Human females are homogametic,meaning they possess two $X$-chromosomes $(44 + XX)$.
During oogenesis,meiosis occurs to produce haploid gametes (ova).
Each mature human ovum contains $22$ autosomes and one $X$-chromosome $(22 + X)$.
Therefore,the correct answer is one $X$-chromosome.

(A) Spermiogenesis is the process of transformation of spermatids into spermatozoa. This process is primarily regulated by $FSH$ (Follicle Stimulating Hormone). $FSH$ acts on the Sertoli cells and stimulates the secretion of some factors which help in the process of spermiogenesis. Therefore,the correct option is $A$.

(D) The germinal epithelium of the seminiferous tubules contains primordial germ cells known as $Spermatogonia$ $(2n)$.
These cells undergo mitosis to increase their number and then differentiate into $Primary$ $spermatocytes$ $(2n)$.
$Primary$ $spermatocytes$ undergo meiosis $I$ to form $Secondary$ $spermatocytes$ $(n)$.
$Secondary$ $spermatocytes$ undergo meiosis $II$ to form $Spermatids$ $(n)$.
Finally,$Spermatids$ undergo a process called $Spermiogenesis$ to transform into $Spermatozoa$ $(n)$.
Therefore,the cells that directly transform into spermatozoa are $Spermatids$.

(C) Gametogenesis involves the formation of haploid gametes from diploid germ cells.
Reduction division, also known as $Meiosis-I$, is the process where the chromosome number is reduced to half.
In both spermatogenesis and oogenesis, this reduction occurs during the $first$ $maturation$ $division$ ($Meiosis-I$).
Therefore, the correct option is $C$.

(A) Capacitation is the physiological maturation process that spermatozoa undergo within the female reproductive tract.
During this process,the glycoprotein coat and seminal plasma proteins are removed from the surface of the sperm's acrosome.
This change increases the fluidity of the sperm membrane and enhances the motility of the sperm,which is essential for the sperm to penetrate the zona pellucida of the ovum.
Therefore,the correct answer is $A$.

(C) The germinal epithelium is a layer of specialized cells that lines the gonads (testes and ovaries).
In both the testes (specifically the seminiferous tubules) and the ovaries,these cells are cuboidal in shape and are responsible for the production of gametes (sperm and ova,respectively) through the process of gametogenesis.
Therefore,the germinal epithelium is present in both.

(A) The process of releasing a mature ovum (secondary oocyte) from the Graafian follicle of the ovary is known as $Ovulation$.
$Parturition$ refers to the process of childbirth.
$Implantation$ is the attachment of the blastocyst to the uterine wall.
$Fertilization$ is the fusion of the male and female gametes.

(C) In human females,the process of oogenesis begins during embryonic development.
Primary oocytes are formed and arrested at the prophase-$I$ stage of meiosis-$I$.
Upon reaching puberty,these follicles mature periodically.
The primary oocyte within the tertiary follicle grows and completes its first meiotic division,resulting in the formation of a large haploid secondary oocyte and a tiny first polar body.
The secondary oocyte then proceeds to meiosis-$II$ but gets arrested at the metaphase-$II$ stage.
This secondary oocyte is the form that is released from the ovary during ovulation.

(D) After ovulation,the secondary oocyte is released from the Graafian follicle.
This oocyte is surrounded by a non-cellular layer called the $Zona$ $pellucida$,which is secreted by the oocyte itself.
Outside the $Zona$ $pellucida$,there are several layers of follicular cells known as the $Corona$ $radiata$.
Therefore,the mammalian egg is covered by both the $Zona$ $pellucida$ and the $Corona$ $radiata$ immediately after ovulation.
Thus,the correct option is $D$.

(C) The mammalian sperm is composed of four parts: head,neck,middle piece,and tail.
The middle piece contains numerous mitochondria arranged in a spiral pattern (also known as the mitochondrial spiral or Nebenkern).
These mitochondria provide the energy in the form of $ATP$ required for the motility of the sperm tail.

(C) After ovulation,the ruptured Graafian follicle transforms into a temporary endocrine structure known as the $Corpus \ luteum$.
This structure is responsible for the secretion of large amounts of $Progesterone$,which is essential for the maintenance of the endometrium for implantation of the fertilized ovum and other events of pregnancy.
Therefore,the correct option is $C$.

(D) The head of a mammalian sperm is typically $hook-shaped$ or $oval$ in many species, including humans. It contains a haploid nucleus and is capped by the acrosome, which is essential for penetrating the egg during fertilization.

(B) Spermatogenesis is the process of formation of sperms from immature germ cells in males. This process occurs within the $Seminiferous \text{ } tubules$ of the testes. The germinal epithelium lining the seminiferous tubules contains spermatogonia, which undergo meiosis to produce spermatozoa.

(A) In humans,the secondary oocyte remains arrested at the metaphase-$II$ stage of meiosis-$II$. The process of meiosis-$II$ is completed only when a sperm enters the secondary oocyte. Upon the entry of the sperm,the secondary oocyte undergoes the second meiotic division,which is unequal and results in the formation of a large haploid ovum (ootid) and a tiny 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).

(C) 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 implantation of the fertilized ovum.
If fertilization does not occur,the $Corpus \ luteum$ degenerates into a scar tissue called $Corpus \ albicans$.

(C) The primary egg membrane is secreted by the oocyte itself. In mammals, the $Zona \text{ } pellucida$ is a thick, transparent, non-cellular glycoprotein layer surrounding the plasma membrane of the oocyte. It is considered the primary egg membrane because it is secreted by the oocyte. The $Corona \text{ } radiata$ is a secondary layer formed by follicular cells, and the $Chorion$ is an extra-embryonic membrane.

(C) In mammals,the testes are located outside the abdominal cavity within a pouch called the scrotum.
The scrotum maintains the temperature of the testes $2-2.5^{\circ}C$ lower than the normal internal body temperature.
This lower temperature is essential for spermatogenesis (the production and maturation of sperm),as higher temperatures can inhibit the process and damage sperm viability.

(B) The middle piece of the sperm contains mitochondria arranged in a spiral manner,which provides energy for sperm motility. This mitochondrial spiral is known as the $Nebenkern$ (or $Nebenkern$ body). The cytoplasmic layer surrounding the mitochondria in the middle piece is specifically referred to as the $Manchette$.

(C) In human females,the process of oogenesis is initiated during the embryonic development stage when millions of oogonia (gamete mother cells) 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 meiosis 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.
Therefore,the maximum number of primary follicles is present in the ovaries at the time of birth,as they undergo atresia (degeneration) throughout childhood and puberty.

(B) In the process of gametogenesis,the first meiotic division $(Meiosis-I)$ is a reductional division.
In males,the primary spermatocyte undergoes $Meiosis-I$ to form two haploid secondary spermatocytes.
In females,the primary oocyte completes $Meiosis-I$ within the tertiary follicle to form a large haploid secondary oocyte and a small first polar body.
Therefore,the secondary spermatocyte and secondary oocyte are the products of the first meiotic division.

(C) In the human female,the process of oogenesis begins during embryonic development.
Primary oocytes are arrested at the prophase-$I$ stage of meiosis-$I$.
Under the influence of the $LH$ surge,the primary oocyte within the Graafian follicle completes meiosis-$I$ to form a large haploid secondary oocyte and a tiny first polar body.
Therefore,the secondary oocyte is released from the ovary (ovulation) after the completion of meiosis-$I$.

(D) The sperm head contains a cap-like structure called the acrosome.
The acrosome is filled with enzymes that help in the fertilization of the ovum.
These enzymes are collectively known as sperm lysins.
Hyaluronidase is a key lytic enzyme present in the acrosome,which helps the sperm to penetrate the layers of the ovum (specifically the corona radiata) by digesting the hyaluronic acid present in the intercellular matrix.
Therefore,the correct option is $D$.

(D) $Graafian$ follicle is the mature ovarian follicle that contains a secondary oocyte.
Inside the $Graafian$ follicle,the secondary oocyte is surrounded by the zona pellucida and layers of follicular cells.
Upon ovulation,the secondary oocyte is released from the $Graafian$ follicle.
Therefore,the correct answer is $D$.

(D) 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 produce $400$ spermatozoa,the number of secondary spermatocytes required is $400 / 2 = 200$.

(B) The $Acrosome$ is a cap-like structure present on the anterior portion of the sperm head. It contains hydrolytic enzymes (such as hyaluronidase) that help in dissolving the egg membrane (zona pellucida), thereby facilitating the entry of the sperm into the egg during fertilization.

(B) During the process of spermiogenesis,the spermatid undergoes significant morphological changes to transform into a functional sperm.
One of the key transformations involves the Golgi apparatus.
The Golgi complex of the spermatid modifies and condenses to form the acrosomal cap,which sits over the anterior portion of the nucleus.
This acrosome contains hydrolytic enzymes that are essential for penetrating the egg during fertilization.

(B) Spermatogenesis consists of three main phases: the multiplication phase,the growth phase,and the maturation phase.
$1$. The multiplication phase involves the rapid mitotic division of spermatogonia.
$2$. The growth phase involves the accumulation of nutrients and increase in size of the spermatogonia to form primary spermatocytes.
$3$. The maturation phase involves meiosis (meiosis-$I$ and meiosis-$II$) to form spermatids.
Among these,the growth phase is the longest phase because the spermatogonia must synthesize significant amounts of cytoplasm,proteins,and organelles to prepare for the subsequent meiotic divisions.

(C) microlecithal egg is an egg that contains a very small amount of yolk (stored food).
In humans,the ovum is alecithal or microlecithal because the embryo receives nutrition directly from the mother through the placenta.
Frog eggs are mesolecithal,insect eggs are centrolecithal,and most fish eggs are telolecithal or macrolecithal.

(B) In the human female,the process of oogenesis initiates during the embryonic development stage.
Millions of gamete mother cells (oogonia) are formed within each fetal ovary.
These oogonia 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 only primary oocytes.

(C) The sperm consists of a head,neck,middle piece,and tail. The middle piece contains numerous mitochondria,which produce energy for the movement of the tail that facilitates sperm motility.

(C) Homolecithal or isolecithal eggs are those in which the yolk is very small in amount and is uniformly distributed throughout the cytoplasm.
These types of eggs are characteristic of organisms that have little need for a large yolk supply during early development,often because the embryo develops quickly or receives nourishment from the mother.
Examples include Amphioxus (cephalochordates),Tunicates (urochordates),and Eutherian mammals (which have microlecithal eggs that are essentially isolecithal).

(A) Human eggs are classified as $Alecithal$ (or sometimes $Microlecithal$ in older texts) because they contain a very negligible or almost no amount of yolk.
Since the human embryo receives nutrition directly from the mother through the placenta,there is no need for a large amount of stored yolk in the egg.

(D) In the mammalian testis,sperm are produced in large numbers to ensure fertilization. They remain inactive (immotile) within the testis and the epididymis until they are ejaculated and undergo capacitation in the female reproductive tract. Oviductal peristalsis is a mechanism in the female reproductive tract that helps in the transport of sperm and the ovum,not an adaptation of the testis. Therefore,the most appropriate answer regarding adaptations within the testis is that they are produced in large numbers and remain inactive until ejaculation. Since both $A$ and $B$ are correct,the best choice is $D$.

(C) The process of spermatogenesis involves the following stages:
$1$. $Spermatogonia$ $(2n)$: These are the immature germ cells that undergo mitosis.
$2$. $Primary$ $Spermatocytes$ $(2n)$: Formed from spermatogonia,these undergo meiosis $I$.
$3$. $Secondary$ $Spermatocytes$ $(n)$: Formed after meiosis $I$,these undergo meiosis $II$.
$4$. $Spermatids$ $(n)$: These are the haploid cells formed after meiosis $II$.
$5$. $Spermatozoa$ $(n)$: These are the mature,motile sperm cells formed through the process of spermiogenesis.
Therefore,the correct sequence is $Spermatogonia \rightarrow Spermatocyte \rightarrow Spermatid \rightarrow Spermatozoa$.

(D) The process of spermatogenesis occurs in the following sequence:
$1$. $Spermatogonia$ (diploid germ cells) undergo mitosis.
$2$. These differentiate into $Primary Spermatocytes$ (diploid).
$3$. $Primary Spermatocytes$ undergo meiosis-$I$ to form $Secondary Spermatocytes$ (haploid).
$4$. $Secondary Spermatocytes$ undergo meiosis-$II$ to form $Spermatids$ (haploid).
$5$. $Spermatids$ transform into $Spermatozoa$ $(Sperm)$ through the process of spermiogenesis.
Therefore, the correct sequence is: $Spermatogonia \rightarrow Primary Spermatocyte \rightarrow Secondary Spermatocyte \rightarrow Spermatid \rightarrow Sperm$.

(C) The middle piece of the sperm contains numerous mitochondria.
These mitochondria produce energy in the form of $ATP$ for the movement of the sperm tail,which facilitates sperm motility.
Due to this energy production,the middle piece is often referred to as the powerhouse of the sperm.

(A) The $Antrum$ is a characteristic fluid-filled cavity found in the secondary and tertiary ovarian follicles during the process of oogenesis.
As the primary follicle develops into a secondary and then a tertiary follicle,the follicular cells proliferate and secrete a fluid into the central space,which is known as the $Antrum$.

(C) After ovulation,the ruptured Graafian follicle transforms into a temporary endocrine structure known as the corpus luteum. This process is triggered by the surge of Luteinizing Hormone $(LH)$. The corpus luteum secretes large amounts of progesterone,which is essential for the maintenance of the endometrium.

(A) The term 'alecithal' is derived from the Greek word 'a' (meaning without) and 'lecithos' (meaning yolk).
Therefore,an alecithal egg is one that contains no yolk or a negligible amount of yolk.
Examples include the eggs of placental mammals,including humans.