The Pistil, Megasporangium (ovule) and Embryo sac Questions in English

(C) In gymnosperms,the megaspore mother cell undergoes meiosis to form four megaspores.
These four megaspores are typically arranged in a $Linear$ row,known as a $Linear$ tetrad.
Out of these four,usually only one functional megaspore develops into the female gametophyte,while the others degenerate.

(A) In $Cycas$ (a gymnosperm),the megasporophyll is a leaf-like structure that bears ovules. In angiosperms,the female reproductive organ is the carpel (or pistil),which also bears ovules. Therefore,the megasporophyll of $Cycas$ is homologous to the carpel of angiosperms.

(C) The pistil (or carpel) consists of three parts: the stigma,the style,and the ovary.
$(c)$ The stigma is the terminal receptive portion of the pistil that serves as a landing platform for pollen grains during the process of pollination.

(A) The Gynoecium (pistil) consists of three parts: the stigma, the style, and the ovary.
$1$. The $Stigma$ is the terminal receptive portion of the carpel that serves as a landing platform for pollen grains.
$2$. The $Style$ is the elongated, slender part beneath the stigma.
$3$. The $Ovary$ is the enlarged basal part containing the ovules.
Therefore, the part that receives the pollen is the $Stigma$.

(D) The silken threads or 'hair' found on a cob of corn are elongated $styles$ that extend from the ovary to the exterior of the husk to receive pollen. The terminal portion of these threads acts as the $stigma$. Therefore, they are collectively referred to as $stigmas$ and $styles$.

(A) In most flowering plants,one megaspore mother cell $(MMC)$ undergoes meiosis to form four haploid megaspores.
Out of these four,three megaspores degenerate,and only one functional megaspore develops into the female gametophyte (embryo sac).
This type of development is known as monosporic development.

(A) Antipodal cells are located at the chalazal end of the embryo sac.
In many angiosperms,these cells enlarge and develop haustorial functions to absorb nutrients from the surrounding nucellus to nourish the developing embryo.
Therefore,the correct answer is $A$.

(A) In a $Hemitropous$ ovule, the body of the ovule is placed transversely at a right angle $(90^{\circ})$ to the stalk (funiculus).
This orientation makes the ovule appear horizontal.
Therefore, the correct answer is $Hemitropous$.

(D) In tetrasporic embryo sac development,all four megaspore nuclei,which are formed after meiosis of the megaspore mother cell,participate in the formation of the female gametophyte (embryo sac). Unlike monosporic or bisporic types where only one or two nuclei contribute,in the tetrasporic type,all four haploid nuclei derived from the megaspore mother cell are involved in the development of the mature embryo sac.

(D) In the process of embryo sac development,the megaspore mother cell undergoes meiosis to produce four haploid megaspores.
Three of these degenerate,and the remaining functional megaspore undergoes three successive mitotic divisions to form an eight-nucleate embryo sac.
The synergids are part of the egg apparatus located at the micropylar end of the embryo sac.
Since they are formed from the mitotic division of a haploid megaspore,they are haploid $(n)$.

(A) The root cells are diploid $(2n)$ in nature. Given that the number of chromosomes in root cells is $14$,we have $2n = 14$,which implies $n = 7$.
Synergid cells are part of the embryo sac and are haploid $(n)$ in nature,as they are formed through meiotic division.
Therefore,the number of chromosomes in the synergid cells will be $n = 7$.

(C) The $Drusa$ type of embryo sac is a type of tetrasporic embryo sac development.
In this type,all four megaspore nuclei participate in the formation of the embryo sac.
It results in a mature embryo sac that is $15$-celled and $16$-nucleate.
This is observed in the genus $Drusa$ (family $Apiaceae$).

(B) In the $Plumbagella$ type of embryo sac development,the megaspore nuclei do not fuse to form a triploid nucleus at the chalazal end.
In this type,the embryo sac is tetrasporic,but the arrangement and fusion of nuclei differ from other types like $Fritillaria$ or $Adoxa$.
Specifically,in $Plumbagella$ type,the mature embryo sac is $4$-nucleate,and the fusion of nuclei to form a triploid structure at the chalazal end does not occur as it does in the $Fritillaria$ type.

(A) During the development of the embryo sac,the megaspore mother cell $(MMC)$ undergoes meiosis to produce four haploid megaspores.
These four megaspores are arranged in a linear tetrad.
Out of these four megaspores,three degenerate,and only one functional megaspore develops into the embryo sac (monosporic development).
Therefore,the formation of a linear tetrad is a characteristic feature of the development of the embryo sac.

(C) The endosperm mother cell $(EMC)$ in angiosperms is formed by the fusion of two polar nuclei and one male gamete,making it a triploid $(3n)$ structure.
Given that the $EMC$ has $24$ chromosomes,we have $3n = 24$,which implies $n = 8$.
The Megaspore Mother Cell $(MMC)$ is a diploid $(2n)$ structure.
Therefore,the number of chromosomes in the $MMC$ is $2n = 2 \times 8 = 16$.

(C) The ovule is attached to the placenta by means of a stalk called the $Funicle$.
$Pedicel$ is the stalk of a flower.
$Petiole$ is the stalk of a leaf.
$Hilum$ is the junction point where the body of the ovule fuses with the $Funicle$.

(C) In $Campylotropous$ ovules,the body of the ovule is curved,and the embryo sac becomes horse-shoe shaped due to the curvature of the nucellus. This is a characteristic feature of the family $Leguminosae$ and $Cruciferae$.

(A) In the development of the ovule,a single hypodermal cell in the nucellus differentiates into the archesporial cell.
This cell is typically single-celled and is located just beneath the epidermis at the micropylar end of the nucellus.
Therefore,the archesporium is single-celled and hypodermal in origin.

(C) The embryo sac is the female gametophyte in angiosperms.
It develops from a functional megaspore through the process of megagametogenesis.
Therefore,the correct option is $C$.

(C) In angiosperms,the ovule is typically bitegmic,meaning it has two integuments.
In gymnosperms,the ovule is typically unitegmic,meaning it has only one integument.
Therefore,the correct sequence is two for angiosperms and one for gymnosperms.

(B) In a crassinucellate ovule,the megaspore mother cell is cut off from the epidermis by the primary parietal cell.
This results in a massive or well-developed nucellus.
In contrast,a tenuinucellate ovule has a very small or poorly developed nucellus.

(D) In angiosperms,the megaspore mother cell undergoes meiosis to form a linear tetrad of four haploid megaspores.
Out of these four megaspores,the three megaspores located towards the micropylar end degenerate.
The single megaspore located towards the chalazal end remains functional and develops into the embryo sac (female gametophyte).
Therefore,the functional megaspore is the one farthest from the micropyle,which is the fourth one.

(D) The $Polygonum$ type of embryo sac is the most common type of embryo sac found in angiosperms.
It develops from a single functional megaspore,which is why it is called $Monosporic$.
During its development,the nucleus of the functional megaspore undergoes three successive free nuclear mitotic divisions,resulting in the formation of $8$ nuclei.
Therefore,it is characterized as $Monosporic$ and $eight-nucleate$.

(B) The angiosperm ovule is considered to be an integumented megasporangium.
In evolutionary biology,the development of the ovule involved the protection of the megasporangium (nucellus) by one or two protective layers known as integuments.
Therefore,the structure evolved from a simple megasporangium into an integumented megasporangium to provide better protection and nourishment to the developing embryo sac.

(B) The functional megaspore undergoes $3$ successive free nuclear mitotic divisions to form an $8$-nucleated embryo sac.
First,the nucleus of the functional megaspore divides mitotically to form two nuclei,which move to the opposite poles.
These two nuclei undergo two more successive mitotic divisions,resulting in the formation of $4$-nucleate and later $8$-nucleate stages of the embryo sac.

(D) An anatropous ovule is the most common type of ovule in angiosperms.
In this type, the body of the ovule becomes completely inverted during development, such that the micropyle comes to lie very close to the hilum.
Consequently, the micropyle is positioned side by side with the funicle.

(D) The $Archegonium$,$Oogonium$,and $Antheridium$ are all reproductive structures found in non-flowering plants (like algae,bryophytes,and pteridophytes) that produce gametes. Specifically,$Archegonium$ and $Oogonium$ are female reproductive organs,while $Antheridium$ is a male reproductive organ. In contrast,the $Ovule$ is a structure found in seed-bearing plants (gymnosperms and angiosperms) that develops into a seed after fertilization. Therefore,the $Ovule$ is the odd one out as it represents a more complex structure associated with seed development,whereas the others are simple gametangia.

(C) The $Embryo$ $sac$ (also known as the female gametophyte) is the microscopic structure located within the ovule of a flowering plant.
It typically consists of $7$ cells and $8$ nuclei.
Among these, the two polar nuclei are located in the large central cell of the $Embryo$ $sac$.
Therefore, the correct structure containing polar nuclei is the $Embryo$ $sac$.

(D) The $Synergids$ possess a specialized cellular thickening at the micropylar end called the $Filiform$ $apparatus$.
This structure plays a crucial role in guiding the entry of the pollen tube into the $Synergid$ by secreting chemical substances.

(A) In an orthotropous ovule,the body of the ovule is straight and not curved.
As a result,the micropyle,chalaza,and the funiculus all lie in a single straight vertical line.
This is considered the most primitive type of ovule and is found in members of the families Polygonaceae and Urticaceae.

(A) The ovule in pea $(Pisum \text{ } sativum)$ is $anatropous$.
In an $anatropous$ ovule, the body of the ovule becomes completely inverted during development so that the micropyle and the funicle come to lie very close to each other.
This is the most common type of ovule found in angiosperms, including the family $Fabaceae$ to which the pea belongs.

(C) mature embryo sac of an angiosperm is $7$-celled and $8$-nucleated.
It consists of $3$ antipodal cells,$2$ synergids,$1$ egg cell,and $1$ central cell containing $2$ polar nuclei.
Therefore,the total number of cells is $3 + 2 + 1 + 1 = 7$ cells,while the total number of nuclei is $3 + 2 + 1 + 2 = 8$ nuclei.

(B) typical angiosperm embryo sac is $7$-celled and $8$-nucleate at maturity.
It consists of:
$1$. An egg apparatus containing $1$ egg cell and $2$ synergids.
$2$. Three antipodal cells located at the chalazal end.
$3$. $A$ large central cell containing $2$ polar nuclei (which eventually fuse to form a secondary nucleus).
Therefore,the embryo sac contains the egg,synergids,polar nuclei,and antipodals.

(B) In angiosperms,the female gametophyte is known as the embryo sac.
It typically consists of $7$ cells and $8$ nuclei.
The embryo sac develops from the functional megaspore through three successive mitotic divisions.
Therefore,the embryo sac represents the female gametophyte in flowering plants.

(C) In a $Campylotropous$ ovule,the body of the ovule is curved,but the embryo sac remains relatively straight.
$Capsella$ and $Capparis$ are classic examples of plants that possess $Campylotropous$ ovules.
Therefore,the correct option is $C$.

(B) The process of formation of the embryo sac from the functional megaspore is known as megagametogenesis.
In this process,the nucleus of the functional megaspore undergoes mitotic divisions to form the female gametophyte (embryo sac).

(A) The Polygonum-type embryo sac is the most common type of embryo sac in angiosperms.
It is $7$-celled and $8$-nucleate at maturity.
It consists of $3$ antipodal cells,$2$ synergids,$1$ egg cell (together forming the egg apparatus),and $1$ large central cell containing $2$ polar nuclei (which fuse to form a secondary nucleus).
Thus,the total count is $7$ cells and $8$ nuclei.

(D) In a flowering plant,the diploid chromosome number $(2n)$ is given as $12$.
Therefore,the haploid chromosome number $(n)$ is $12 / 2 = 6$.
$A$. Endosperm is typically triploid $(3n)$,so it would have $3 \times 6 = 18$ chromosomes.
$B$. Leaf cells are somatic cells and are diploid $(2n)$,so they would have $12$ chromosomes.
$C$. Cotyledons are part of the embryo and are diploid $(2n)$,so they would have $12$ chromosomes.
$D$. Synergids are part of the embryo sac and are haploid $(n)$,so they possess $6$ chromosomes.
Thus,the correct option is $D$.

(A) The egg apparatus of an angiosperm is $3$-celled. It consists of one egg cell and two synergids located on either side of the egg cell.
$3$ antipodal cells are present at the chalazal end.
The secondary nucleus (formed by the fusion of two polar nuclei) is present in the center of the embryo sac.

(D) The funicle is the stalk that attaches the ovule to the placenta.
The point of attachment where the funicle joins the main body of the ovule is known as the $Hilum$.
Therefore,the $Hilum$ represents the junction between the ovule and the funicle.

(C) After meiotic division,four haploid megaspores are formed.
Only one megaspore (haploid) remains functional and divides mitotically to form the embryo sac.
The other three megaspores degenerate or disintegrate.

(D) In an anatropous ovule,the body of the ovule becomes completely inverted due to unilateral growth of the funicle.
As a result of this $180^{\circ}$ rotation,the micropyle comes to lie close to the hilum,pointing downwards towards the placenta.
Therefore,the micropyle is directed downwards.

(A) The $Polygonum$ type embryo sac is formed from a single functional megaspore through three rounds of mitosis,resulting in an $8$-nucleate and $7$-celled structure.
Since the megaspore is the product of meiosis,all cells within the mature embryo sac,including the synergids,the egg cell,and the antipodal cells,are haploid $(n)$.
In contrast,the surrounding tissues of the ovule,such as the integuments and nucellus,are diploid $(2n)$.

(A) In the development of an embryo sac,a single megaspore mother cell $(MMC)$ undergoes meiosis to produce four megaspores.
In monosporic development,only one megaspore is functional.
In tetrasporic development,all four megaspore nuclei participate in the formation of the embryo sac.
Since all four nuclei originate from the meiosis of a single $MMC$,only $1$ megaspore mother cell is required for the formation of a tetrasporic embryo sac.

(A) The $Megaspore$ $mother$ $cell$ $(MMC)$ undergoes meiosis to form four megaspores.
Out of these four,usually one megaspore remains functional and develops into the embryo sac (female gametophyte).
Depending on the number of megaspore nuclei participating in the development,the embryo sac formation is classified as monosporic,bisporic,or tetrasporic.
Therefore,the embryo sac originates from the megaspore mother cell.

(C) In a $Hemitropous$ ovule,the body of the ovule is placed transversely at a right angle $(90^{\circ})$ to the funicle.
In $Anatropous$ ovules,the body is inverted.
In $Orthotropous$ ovules,the micropyle,chalaza,and funicle lie in a straight line.
In $Campylotropous$ ovules,the body of the ovule is curved,but the embryo sac is not straight.

(C) In most angiosperms,the mature embryo sac (female gametophyte) is formed through the process of megasporogenesis followed by three successive mitotic divisions of the functional megaspore.
These divisions result in $8$ nuclei.
After the divisions,cell walls are laid down,leading to the organization of the typical female gametophyte.
It consists of $3$ antipodal cells,$2$ synergids,$1$ egg cell,and $1$ large central cell containing $2$ polar nuclei.
Thus,the mature embryo sac is $7$-celled (because the central cell is one cell with two nuclei) and $8$-nucleate.

(A) An ovule where the funiculus lies close to the micropyle due to the rotation of the ovule body by $180^{\circ}$ is called an anatropous ovule.
In a campylotropous ovule, the body of the ovule is curved, and the micropyle is directed towards the funiculus but not as closely as in the anatropous type.
In an atropous (or orthotropous) ovule, the micropyle, chalaza, and funiculus lie in a single straight line.
Therefore, the correct answer is $A$.

(A) The ovule is attached to the placenta by means of a stalk called the $Funicle$.
$Hilum$ is the junction point where the $Funicle$ attaches to the body of the ovule.
$Raphe$ is the ridge formed by the $Funicle$ fused with the ovule body in anatropous ovules.
$Chalaza$ represents the basal part of the ovule opposite to the micropyle.