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

(D) The gynoecium represents the female reproductive part of a flower, consisting of one or more carpels (pistils).
Each carpel is composed of three distinct parts: the stigma, the style, and the ovary.
$1$. The $Stigma$ serves as the landing platform for pollen grains.
$2$. The $Style$ is the elongated, slender part beneath the stigma.
$3$. The $Ovary$ is the basal, swollen part that contains the ovules.
Therefore, the part that receives the pollen is the $Stigma$.

(B) In a mature female gametophyte (embryo sac) of a typical angiosperm, there are $3$ antipodal cells at the chalazal end, $2$ synergids and $1$ egg cell at the micropylar end, and $1$ large central cell containing $2$ polar nuclei.
Although it contains $8$ nuclei, the fusion of the $2$ polar nuclei into a single diploid secondary nucleus results in a total of $7$ cells.
Therefore, the mature embryo sac is $7$-celled and $8$-nucleated.

(A) In a typical $8$-nucleate embryo sac,there are four nuclei at the micropylar end and four nuclei at the chalazal end.
One nucleus from the micropylar quartet and one nucleus from the chalazal quartet migrate to the centre of the embryo sac.
These two nuclei are known as polar nuclei,which eventually fuse to form a single diploid secondary nucleus.

(A) The development of the embryo sac (female gametophyte) follows a specific sequence:
$1$. The archesporial cell differentiates in the nucellus.
$2$. It functions as the megaspore mother cell $(MMC)$.
$3$. The $MMC$ undergoes meiosis to form four haploid megaspores.
$4$. Three megaspores degenerate,and the remaining functional megaspore develops into the embryo sac through mitosis.

(A) The process of megasporogenesis and megagametogenesis follows this sequence:
$1$. Differentiation of megaspore mother cells $(i)$.
$2$. Meiosis of the megaspore mother cell $(ii)$.
$3$. Formation of a linear tetrad $(iii)$.
$4$. Degeneration of $3$ megaspores $(v)$.
$5$. Mitotic division of the functional megaspore $(iv)$.
$6$. Formation of embryo sac $(vi)$.
$7$. Fusion of polar nuclei $(vii)$.
Therefore,the correct sequence is $(i), (ii), (iii), (v), (iv), (vi), (vii)$.

(C) . The $Obturator$ is a specialized tissue structure found near the micropyle of the ovule. It functions by guiding the growth of the pollen tube towards the micropyle,effectively acting as a bridge to facilitate successful fertilization.

(A) The micropyle is a small opening in the integuments of the ovule.
During the process of fertilization,the pollen tube enters the ovule through this micropyle to deliver the male gametes to the embryo sac.
Therefore,it facilitates the entry of the pollen tube into the ovule.

(B) The embryo sac contains different types of cells.
Synergid cells are haploid $(n)$.
Antipodal cells are haploid $(n)$.
The egg cell is haploid $(n)$.
The central cell contains a secondary nucleus which is diploid $(2n)$ before fertilization.
Therefore,the statement that antipodal cells are haploid is correct.

(A) In the embryo sac of angiosperms,two polar nuclei migrate to the center. These two nuclei fuse to form a single diploid $(2n)$ nucleus,which is known as the secondary nucleus or definitive nucleus. Therefore,the secondary nucleus is diploid.

(C) In a haplontic life cycle,the zygote undergoes meiosis to produce four haploid cells (or nuclei). In many organisms exhibiting this cycle (such as certain algae like Chlamydomonas),these four haploid cells develop into new individuals. However,in specific biological contexts involving the formation of spores or gametes where reduction division occurs,if the question refers to the typical meiotic product of a zygote in a haplontic organism,all four cells are usually functional. If the question implies a specific developmental pathway where degeneration occurs (such as in certain megasporogenesis processes),it is important to note that in a standard haplontic life cycle,all four haploid products are typically viable. Given the standard options provided for this specific question type,the answer is $0$. However,if this refers to a scenario where only one survives (like megasporogenesis in angiosperms),the answer would be $3$. Assuming the context of standard textbook questions regarding haplontic cycles,if the question implies the degeneration of nuclei during specific developmental stages,$3$ nuclei degenerate.

(A) In $Thuja$,the ovule is $Orthotropous$ (also known as $Atropous$).
In an $Orthotropous$ ovule,the micropyle,chalaza,and funicle lie in a straight vertical line.
This is considered the most primitive type of ovule and is commonly found in gymnosperms like $Thuja$ and $Cycas$.

(C) In gymnosperms,the megasporangium is the structure that produces megaspores.
In angiosperms,the ovule is the structure that contains the megasporangium (nucellus) and is responsible for the development of the female gametophyte.
Therefore,the megasporangium is equivalent to the ovule in angiosperms.

(B) The pistil or carpel is the female reproductive part of a flower. It consists of three main parts:
$1$. Stigma: The receptive surface for pollen grains.
$2$. Style: The elongated tube that connects the stigma to the ovary.
$3$. Ovary: The enlarged basal part containing ovules.
Among the given options,the style is a part of the pistil. Filament,anther,and connective are parts of the stamen (androecium).

(D) The pistil or carpel, which represents the female reproductive part of a flower, consists of three distinct parts:
$1$. $Stigma$: The receptive surface for pollen grains.
$2$. $Style$: The elongated tube connecting the stigma to the ovary.
$3$. $Ovary$: The enlarged basal part containing the ovules.

(A) In angiosperms,the megasporangium is technically referred to as the ovule.
Inside the ovule,the megaspore mother cell undergoes meiosis to produce megaspores,one of which develops into the embryo sac (female gametophyte).
Therefore,the megasporangium is synonymous with the ovule.

(C) In flowering plants,the nucellus is the central part of the ovule,which is composed of nutritive tissue.
It is protected by one or two protective layers known as integuments (envelopes).
The entire structure,consisting of the nucellus,the integuments,and the funicle,is collectively referred to as the ovule (megasporangium).

(B) In plant biology,the ovule is the structure that gives rise to and contains the female reproductive cells.
Morphologically and developmentally,the ovule is equivalent to the megasporangium,which is the structure where megaspores are produced.
In angiosperms,the ovule is protected by the ovary,while in gymnosperms,it is exposed.
Therefore,the correct answer is $B$ (Megasporangium).

(D) In $Spermatophyta$ (seed-bearing plants, which include Gymnosperms and Angiosperms), the female gametophyte is not free-living.
Instead, it is retained within the megasporangium (ovule) which is part of the sporophyte.
This retention is a critical evolutionary adaptation that protects the developing embryo and ensures successful fertilization within the seed-bearing structures.

(D) In most angiosperms,the embryo sac develops from a single functional megaspore. This is known as monosporic development. The most common type of embryo sac development is the $Polygonum$ type,where the functional megaspore undergoes three successive mitotic divisions to form an $8$-nucleated structure. Therefore,it is called the $Monosporic-Polygonum$ type.

(B) In $Capsella$,the development of the embryo sac is of the $Polygonum$ type.
In this type,the functional megaspore undergoes three successive free nuclear mitotic divisions to form an $8$-nucleate structure.
Since the embryo sac develops from a single functional megaspore,it is known as a $Monosporic$ embryo sac.

(C) In corn (maize),the long,thread-like structures that hang out from the end of the cob are the $styles$ and $stigmas$. These structures are collectively known as 'corn silk'. The $style$ is an elongated part of the carpel that connects the $stigma$ to the $ovary$. In maize,these $styles$ are very long to capture wind-borne pollen grains.

(B) An anatropous ovule is the most common type of ovule found 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 funicle (stalk). Consequently,the micropyle is directed downwards towards the placenta.

(D) The filiform apparatus is a specialized cellular thickening of the synergid cell wall at the micropylar end of the embryo sac. Its primary function is to guide the entry of the pollen tube into the synergid.

(B) In angiosperms,ovules are classified based on the development and amount of nucellus tissue.
$1$. $Crassinucellate$ ovule: In this type,the primary parietal cell is formed,resulting in a massive,multi-layered nucellus.
$2$. $Tenuinucellate$ ovule: In this type,the primary parietal cell is not formed,and the nucellus remains thin,consisting of only a single layer of cells surrounding the embryo sac.
Therefore,an ovule with a single-layered nucellus is called $Tenuinucellate$.

(C) In an $Amphitropous$ ovule,the curvature of the ovule is so pronounced that the embryo sac becomes horse-shoe shaped. Due to this curvature,the funicle and the micropyle come very close to each other. This is a characteristic feature of $Amphitropous$ ovules,commonly found in families like $Alismataceae$ and $Butomaceae$.

(C) In the majority of angiosperms,including the pea plant ($Pisum$ $sativum$),the ovule 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. The micropyle faces the placenta.

(B) In the genus $Papaver$ (poppy),the ovule is of the $Anatropous$ type. 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.

(B) The term 'resupinate' in the context of ovules refers to the inversion of the ovule during development. An $anatropous$ ovule is one that has undergone a $180^{\circ}$ rotation, causing the micropyle to face the funicle. This is the most common type of ovule found in angiosperms. Therefore, the resupinate type of ovule is $anatropous$.

(C) In the process of megasporogenesis,one megaspore mother cell $(MMC)$ undergoes meiosis to produce $4$ megaspores.
Out of these $4$ megaspores,usually only $1$ remains functional,while the other $3$ degenerate.
Therefore,$1$ meiotic division produces $1$ functional megaspore.
To produce $100$ functional megaspores,$100$ meiotic divisions are required.

(B) In the ovule of angiosperms like $Capsella$, the $Nucellus$ is a mass of diploid cells $(2n)$ that surrounds the embryo sac.
Other structures mentioned, such as the $Synergids$ $(n)$ and $Antipodal$ $cells$ $(n)$, are haploid components of the embryo sac.
The $Pollen$ $tube$ is a structure formed during the process of fertilization and is not a part of the ovule itself.

(B) In angiosperms,ovules are classified based on the amount and development of the nucellus.
$1$. Crassinucellate ovules are those in which the megaspore mother cell is formed from a hypodermal archesporial cell that divides to form a primary parietal cell and a primary sporogenous cell.
$2$. This results in a massive or well-developed nucellus because the parietal tissue is formed.
$3$. In contrast,tenuinucellate ovules have a very small or poorly developed nucellus where the archesporial cell functions directly as the megaspore mother cell.

(A) The pistil (or carpel) consists of three main parts: the stigma, the style, and the ovary.
$1$. The $Stigma$ serves as a landing platform for pollen grains.
$2$. The $Style$ is the elongated slender part beneath the stigma.
$3$. The $Ovary$ is the basal bulged part of the pistil that contains the ovules.
Therefore, the correct answer is $Stigma$.

(C) The nucellus is the central part of the ovule in flowering plants. It consists of a mass of parenchymatous tissue enclosed within the integuments. It provides nutrition to the developing embryo sac.

(A) The $Polygonum$ type of embryo sac is the most common type of embryo sac in angiosperms,which is $7$-celled and $8$-nucleate.
In this development,a single megaspore mother cell undergoes meiosis to produce four haploid megaspores.
Three megaspores degenerate,and the remaining functional megaspore undergoes three successive mitotic divisions to form the embryo sac.
Since these divisions are mitotic,all the resulting cells (antipodal cells,synergids,egg cell,and the central cell with two polar nuclei) are haploid $(n)$,except for the central cell which contains two haploid polar nuclei (often fusing to form a diploid secondary nucleus).
Therefore,all the individual cells within the mature $Polygonum$ type embryo sac are haploid.

(A) An ovule that is arranged transversely at right angles to its stalk (funiculus) is known as an $Amphitropous$ ovule. In this type,the embryo sac becomes curved like a horseshoe. Note: In some classifications,$Amphitropous$ is specifically used for transverse orientation,while $Campylotropous$ refers to a curved ovule where the micropyle is directed towards the funiculus.

(A) In a typical angiosperm,the mature embryo sac (also known as the female gametophyte) is $7$-celled and $8$-nucleated.
It consists of:
$1$. Three antipodal cells at the chalazal end.
$2$. One central cell containing two polar nuclei.
$3$. An egg apparatus at the micropylar end,which includes one egg cell and two synergids.
Thus,the total count is $7$ cells and $8$ nuclei.

(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.
As a result of this $180^{\circ}$ rotation,the micropyle comes to lie very close to the hilum and is positioned adjacent to the funicle.

(D) In angiosperms,the embryo sac is the female gametophyte.
It develops from the functional megaspore through the process of megagametogenesis.
Since the embryo sac produces the female gametes (egg cell) and is the haploid stage of the plant life cycle that produces gametes,it is technically referred to as the megagametophyte.
Therefore,the correct option is $D$.

(A) In flowering plants, the megasporangium is technically referred to as the $Ovule$.
Inside the ovule, the megaspore mother cell undergoes meiosis to produce megaspores, which eventually develop into the embryo sac (female gametophyte).
The egg cell is a component of the embryo sac.
Therefore, the structure that houses the development of the egg cell is the $Ovule$.

(C) In angiosperms,the functional megaspore undergoes three successive free nuclear mitotic divisions to form $8$ nuclei.
These nuclei are organized into $7$ cells: $3$ antipodal cells at the chalazal end,$2$ synergids and $1$ egg cell at the micropylar end (forming the egg apparatus),and $1$ large central cell containing $2$ polar nuclei.
Thus,the mature embryo sac is $7$-celled and $8$-nucleate.

(C) In an $Orthotropous$ (or $Atropous$) ovule,the micropyle,chalaza,and funicle lie in a straight vertical line. In this type of ovule,the micropyle is directed towards the chalaza,which is at the base. This is considered the most primitive type of ovule.

(D) In $Capsella$ (a typical dicot),the embryo sac develops within the ovule.
During its development,the embryo sac derives its nutrition from the surrounding tissue known as the $Nucellus$.
The $Nucellus$ acts as a nutritive tissue that provides essential nutrients to the developing embryo sac and the embryo after fertilization.

(B) In angiosperms,the megaspore mother cell undergoes meiosis to produce four haploid megaspores.
Out of these four,three degenerate and one remains functional.
This functional megaspore undergoes three successive mitotic divisions to form an eight-nucleated structure known as the embryo sac (female gametophyte).

(B) In angiosperms,the haploid chromosome number $(n)$ is given as $12$.
$1$. The integuments are part of the ovule and are diploid $(2n)$ structures derived from the parent plant body.
$2$. Therefore,the number of chromosomes in the integuments = $2 \times n = 2 \times 12 = 24$.
$3$. The synergids are part of the embryo sac (female gametophyte) and are haploid $(n)$ cells.
$4$. Therefore,the number of chromosomes in the synergids = $n = 12$.
$5$. Thus,the number of chromosomes in the integuments and synergids is $24$ and $12$ respectively.

(B) In angiosperms,the megaspore mother cell undergoes meiosis to produce four megaspores. Three of these degenerate,and the remaining one functional megaspore develops into the embryo sac. Since the embryo sac is the structure that produces the female gamete (egg cell),it is referred to as the female gametophyte. Therefore,the embryo sac represents the female gametophyte.

(C) In the process of sexual reproduction in flowering plants,the embryo sac is formed within the ovule. The embryo sac typically consists of seven cells and eight nuclei. Among these,the synergids are specialized cells located at the micropylar end of the embryo sac. Since the embryo sac develops from the functional megaspore within the nucellus of the ovule,the synergids are considered to be part of the ovule structure.

(B) In $Capsella$ (a member of the Brassicaceae family),the ovule is $Campylotropous$.
In a $Campylotropous$ ovule,the body of the ovule is curved,and the embryo sac becomes bent in a horse-shoe shape.
This is a characteristic feature of many members of the family Brassicaceae.

(A) In the process of megasporogenesis,a single megaspore mother cell $(MMC)$ undergoes meiosis to produce four haploid megaspores.
Out of these four megaspores,three degenerate,and only one remains functional.
This functional megaspore is typically located at the $Chalazal$ end of the ovule.
This functional megaspore then undergoes mitotic divisions to develop into the female gametophyte,also known as the embryo sac.

(C) In angiosperms,the megaspore mother cell $(MMC)$ undergoes meiosis to produce four haploid megaspores. Out of these four,three degenerate,and only one remains functional. This functional megaspore undergoes three successive rounds of free-nuclear mitotic divisions to form the $8$-nucleated embryo sac (female gametophyte).