Gametogenesis Questions in English

(D) During the process of ovulation,the Graafian follicle ruptures to release the female gamete. At this stage,the oocyte is arrested in the metaphase of meiosis-$II$ and is known as the secondary oocyte. The secondary oocyte is surrounded by the zona pellucida and corona radiata. Therefore,the correct answer is $D$.

(B) The $Zona$ $pellucida$ is a glycoprotein layer surrounding the plasma membrane of an oocyte. It first appears during the development of the $Secondary$ $follicle$ stage, where it begins to form around the primary oocyte. By the time the follicle reaches the $Tertiary$ $follicle$ stage, the $Zona$ $pellucida$ is clearly defined and well-developed.

(B) The correct answer is $B$.
$FSH$ (Follicle Stimulating Hormone) is secreted by the anterior pituitary gland.
It acts on the Sertoli cells present in the seminiferous tubules of the testes.
Upon stimulation by $FSH$,Sertoli cells secrete various factors,including Androgen Binding Protein $(ABP)$,which concentrate testosterone locally and facilitate the process of spermiogenesis (the transformation of spermatids into spermatozoa).

(A) For normal fertility,it is essential that at least $60\%$ of all sperms must have normal shape and size,and at least $40\%$ of them must show vigorous motility. This is a standard physiological requirement for successful fertilization in humans.

(B) In the process of spermatogenesis,the $2n$ (diploid) spermatogonia undergo mitosis to form primary spermatocytes,which are also $2n$ (diploid).
These primary spermatocytes then undergo meiosis $I$ to form secondary spermatocytes,which are $n$ (haploid).
Secondary spermatocytes undergo meiosis $II$ to form spermatids ($n$,haploid),which eventually differentiate into spermatozoa ($n$,haploid).
Therefore,only the primary spermatocytes are diploid $(2n)$.

(B) The process of ovulation is triggered by a rapid surge in the secretion of Luteinizing Hormone $(LH)$ from the anterior pituitary gland. This phenomenon is known as the $LH$ surge. This surge occurs towards the middle of the menstrual cycle (around the $14^{th}$ day) and induces the rupture of the Graafian follicle,leading to the release of the secondary oocyte (ovum). Therefore,the correct option is $B$.

(A) After the process of spermiogenesis,the transformation of spermatids into spermatozoa occurs.
Following this,the sperm heads become embedded in the $Sertoli$ cells to receive nourishment.
Finally,they are released from the seminiferous tubules by the process called spermiation.

(B) Sertoli cells (also known as nurse cells) are specialized cells found within the seminiferous tubules of the testes. Their primary function is to provide structural and metabolic support,as well as nourishment,to the developing germ cells (spermatogonia) during the process of spermatogenesis.

(A) The correct answer is $A$.
In the absence of an acrosome,the sperm cannot penetrate the egg.
The acrosome is a cap-like structure present at the tip of the sperm head.
It contains hydrolytic enzymes,such as hyaluronidase and acrosin,which are essential for digesting the protective layers of the ovum (zona pellucida and corona radiata).
Without these enzymes,the sperm is unable to penetrate the egg,and fertilization cannot occur.

(B) The correct match is $1-s, 2-p, 3-q, 4-r$.
$1$. Head $(s)$: The sperm head contains an elongated haploid nucleus.
$2$. Acrosome $(p)$: The anterior portion of the head is covered by a cap-like structure called the acrosome,which is filled with enzymes that help in the fertilization of the ovum.
$3$. Middle piece $(q)$: The middle piece possesses numerous mitochondria,which produce energy for the movement of the tail.
$4$. Tail $(r)$: The tail facilitates sperm motility,which is essential for fertilization.

(B) During spermatogenesis,one primary spermatocyte undergoes meiosis to produce $4$ functional spermatozoa.
Therefore,$2$ primary spermatocytes will produce $2 \times 4 = 8$ spermatozoa.
During oogenesis,one primary oocyte undergoes meiosis to produce only $1$ functional ovum (and $2-3$ polar bodies which degenerate).
Therefore,$2$ primary oocytes will produce $2 \times 1 = 2$ ova.
The ratio of spermatozoa to ova produced is $8:2$,which simplifies to $4:1$.

(B) The correct answer is $(B)$.
$A$ represents the acrosome,which contains enzymes that help in the penetration of the sperm into the ovum.
$B$ represents the middle piece,which contains numerous mitochondria arranged in a spiral. These mitochondria provide the energy $(ATP)$ required for the movement of the sperm.
$C$ represents the tail,which facilitates the movement of the sperm through the female reproductive tract.

(A) The process of Oogenesis begins with the multiplication of Oogonia $(p)$ in the fetal ovary.
These Oogonia undergo differentiation to form Primary oocytes $(q)$.
The Primary oocyte completes the first meiotic division to form a large Secondary oocyte $(r)$ and a small first polar body.
The Secondary oocyte then undergoes the second meiotic division to form a large Ovum $(s)$ and a second polar body.
Therefore,the correct sequence is $p$ - Oogonia,$q$ - Primary oocyte,$r$ - Secondary oocyte,$s$ - Ovum.

(B) In the process of spermatogenesis,the sequence of cell development is as follows:
$1$. $P$ represents the Primary spermatocyte,which undergoes Meiosis $I$ to form two haploid cells.
$2$. $Q$ represents the Secondary spermatocyte,which is the product of Meiosis $I$ and undergoes Meiosis $II$.
$3$. $R$ represents the Spermatids,which are the haploid cells formed after Meiosis $II$.
$4$. $S$ represents the Spermatozoa (sperm),which are formed from spermatids through the process of spermiogenesis.
Therefore,the correct sequence is $P$ - Primary spermatocyte,$Q$ - Secondary spermatocyte,$R$ - Spermatids,$S$ - Spermatozoa.

(A) The correct answer is $A$ (spermiogenesis).
$1$. The process of transformation of non-motile spermatids into mature,motile spermatozoa is known as spermiogenesis.
$2$. This process represents the final stage of spermatogenesis,where the spermatids undergo structural changes to become functional sperm cells.
$3$. During this phase,the spermatid loses most of its cytoplasm,develops an acrosome,and forms a tail for motility.

(C) The correct answer is $C$.
During fetal development,millions of oogonia are formed in each fetal ovary.
However,no more oogonia are formed or added after birth.
Many of these primary follicles degenerate during the phase from birth to puberty.
As a result,at the time of puberty,only about $60,000-80,000$ primary follicles are left in each ovary.

(C) The correct option is $C$.
$FSH$ (Follicle Stimulating Hormone) acts on the Sertoli cells of the testes.
It stimulates the secretion of some factors which help in the process of spermiogenesis,which is the transformation of spermatids into spermatozoa.

(A) In a primary spermatocyte,the diploid number of chromosomes is $2n = 16$.
During the first meiotic division $(Meiosis-I)$,the homologous chromosomes separate,resulting in the formation of two secondary spermatocytes.
Each secondary spermatocyte receives $n = 8$ chromosomes.
Since each chromosome consists of $2$ sister chromatids,the total number of chromatids in each secondary spermatocyte is $8 \times 2 = 16$.

(C) primary oocyte in the Graafian follicle.
Vitellogenesis is the process of yolk formation and deposition.
It occurs in the primary oocyte within the Graafian follicle during oogenesis in the ovary.
This stage involves the accumulation of yolk,which includes proteins,fats,phospholipids,carbohydrates,and glycogen,all of which are essential for the development of the embryo.

(D) In the process of spermatogenesis,the germinal epithelial cells $(2n)$ undergo mitosis to form spermatogonia $(2n)$.
These spermatogonia grow into primary spermatocytes $(2n)$.
Primary spermatocytes undergo the first meiotic division (meiosis-$I$) to form two secondary spermatocytes $(n)$.
Since secondary spermatocytes are formed after the first meiotic division,they are haploid $(n)$ cells.
Therefore,the correct option is $D$.

(D) In the process of gametogenesis,a single primary spermatocyte (male germ cell) undergoes meiosis to produce $4$ functional sperms.
Conversely,a single primary oocyte (female germ cell) undergoes meiosis to produce only $1$ functional ovum and $3$ non-functional polar bodies.
Therefore,the ratio of ova produced to sperms produced from one germ cell each is $1:4$.

(C) The correct answer is $C$.
Sertoli cells are specialized cells found within the seminiferous tubules of the testes.
Their primary function is to provide nourishment,structural support,and protection to the developing germ cells (spermatids) during the process of spermatogenesis.

(A) The correct answer is $A$.
$1$. The testes are the primary male reproductive organs responsible for the production of sperms and the secretion of male sex hormones.
$2$. The scrotum is a pouch of skin that holds the testes outside the abdominal cavity.
$3$. This external position is crucial because it maintains the temperature of the testes at $2-2.5^{\circ}C$ lower than the normal internal body temperature.
$4$. This lower temperature is essential for the process of normal spermatogenesis,as higher temperatures can inhibit sperm production.

(A) Based on the biological structure of an ovum (oocyte):
$1$. The outermost layer of follicular cells is the $Corona \text{ } radiata$ (labeled $Y$ in the diagram).
$2$. The thick,transparent glycoprotein layer surrounding the oocyte membrane is the $Zona \text{ } pellucida$ (labeled $X$ in the diagram).
$3$. The space between the $Zona \text{ } pellucida$ and the oocyte membrane is the $Perivitelline \text{ } space$ (labeled $Z$ in the diagram).
Therefore,the correct identification is $X$ - $Zona \text{ } pellucida$,$Y$ - $Corona \text{ } radiata$,$Z$ - $Perivitelline \text{ } space$.

(D) The structures surrounding the ovum from the outside to the inside are as follows:
$1$. Corona radiata (outermost layer consisting of follicular cells).
$2$. Zona pellucida (a glycoprotein layer).
$3$. Perivitelline space (the space between the zona pellucida and the plasma membrane).
$4$. Plasma membrane of the ovum (innermost boundary).
Therefore,the correct sequence from outer to inner is $C, A, B, D$.

(B) is incorrect because spermatogonia initially undergo mitotic divisions to increase their population.
$B$ is incorrect because primary spermatocytes undergo meiosis $I$ to form secondary spermatocytes.
$C$ is correct because secondary spermatocytes undergo meiosis $II$ to produce haploid spermatids.
$D$ is incorrect because the transformation of spermatids into spermatozoa is a process of structural remodeling called spermiogenesis,not mitosis.
$E$ is correct because the process of transformation of spermatids into spermatozoa is known as spermiogenesis.
Therefore,the correct statements are $C$ and $E$.