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

(A) mature angiosperm embryo sac is typically $7$-celled and $8$-nucleate.
It consists of three antipodal cells at the chalazal end,two synergids and one egg cell at the micropylar end,and a large central cell containing two polar nuclei.
Image $A$ correctly depicts this structure with three antipodal cells at the top (chalazal end),two synergids and one egg cell at the bottom (micropylar end),and two polar nuclei in the central cell.

(A) In the provided diagram of an anatropous ovule:
$C$ represents the outer integument.
$A$ represents the inner integument.
$D$ represents the nucellus (the central mass of tissue).
$B$ represents the embryo sac.
Therefore,the statement '$D$ - Inner integument' is incorrect because $D$ points to the nucellus,while $A$ points to the inner integument.

(B) The egg apparatus consists of two synergids and one egg cell.
In angiosperms,the most common type of embryo sac is the $Polygonum$ type.
It is $7$-celled and $8$-nucleate.
The nuclei are arranged such that three are organized at the micropylar end to form the egg apparatus (one egg cell and two synergids).
Two nuclei migrate to the center to form polar nuclei within a single central cell.
Three nuclei at the chalazal pole are organized into antipodal cells.

(C) The $Polygonum$ type of embryo sac is the most common type found in angiosperms.
It is $7$-celled and $8$-nucleate.
The nuclei are arranged such that three are organized at the micropylar end to form the egg apparatus (one egg cell and two synergids).
Two nuclei migrate to the center to form polar nuclei within a single central cell.
Three nuclei at the chalazal pole are organized into antipodal cells.

(D) An ideal embryo sac contains $7$ cells and $8$ nuclei.
$3$ cells are present at the micropylar end forming the egg apparatus,which consists of one egg cell and two synergids.
One large central cell is present in the middle of the embryo sac,which contains two polar nuclei.
The remaining $3$ cells are present at the chalazal end and are known as antipodal cells.
Therefore,all the given options are components of the embryo sac.

(A) In the process of megasporogenesis,a single cell of the nucellus,usually towards the micropylar end,differentiates into the megaspore mother cell $(MMC)$.
The nucellus is the central part of the ovule that provides nutrition to the developing embryo sac.

(B) In angiosperms,the female gametophyte is commonly referred to as the embryo sac. It is a small structure located within the ovule that contains the egg cell,which is essential for fertilization.

(B) In angiosperms,the functional megaspore undergoes mitotic divisions to develop into the female gametophyte,which is known as the embryo sac.

(B) In gymnosperms,the endosperm is formed before fertilization and is a haploid $(n)$ tissue derived directly from the female gametophyte. In angiosperms,the embryo sac represents the female gametophyte. Therefore,ontogenetically,the gymnosperm endosperm is equivalent to the female gametophyte or the embryo sac of angiosperms.

(B) In angiosperms,the female gametophyte is known as the embryo sac.
It is a $7$-celled and $8$-nucleate structure that develops within the ovule.
The embryo is the result of fertilization (diploid),the endosperm is the nutritive tissue formed after double fertilization (usually triploid),and the synergid is a specific cell type found within the embryo sac.

(C) The embryo sac,also known as the female gametophyte,is a structure found within the ovule of flowering plants (angiosperms).
It develops from the functional megaspore through the process of megagametogenesis.
The ovule contains the embryo sac,which houses the egg cell and other associated cells (synergids and antipodals) necessary for fertilization.
Therefore,the correct location of the embryo sac is the ovule.

(B) The $mega-gametophyte$ or female gametophyte,which is also called the embryo sac,is typically a $7$-celled and $8$-nucleate structure in angiosperms.

(A) The chalazal pole is located exactly opposite to the micropylar end of the ovule.
It represents the basal part of the ovule where the integuments originate.

(A) The embryo sac (female gametophyte) contains seven cells and eight nuclei. Two of these nuclei,known as polar nuclei,are situated in the central cell. During double fertilization,these polar nuclei fuse with one of the male gametes to form the primary endosperm nucleus $(PEN)$ through a process called triple fusion.

(A) The funicle (or funiculus) is the stalk-like structure that attaches the ovule to the placenta within the ovary of a flowering plant.

(B) In the embryo sac of an angiosperm,the egg apparatus is located towards the micropylar pole.
It typically consists of two synergids and one egg cell.
The egg cell contains a large vacuole at its upper end and a prominent nucleus near its lower end.
Synergids possess a specialized cellular thickening called the filiform apparatus at their micropylar end.
This apparatus is responsible for attracting and guiding the pollen tube into the synergid.

(B) The $Polygonum$ type of embryo sac is the most common in angiosperms. It is $7$-celled and $8$-nucleate at maturity.
The nuclei are arranged such that three are organized at the micropylar end to form the egg apparatus (one egg cell and two synergids).
Two nuclei migrate to the center to form polar nuclei within a single large central cell.
Three nuclei at the chalazal pole are organized into antipodal cells.

(C) The correct answer is the Central cell.
In a mature angiosperm embryo sac,six out of the eight nuclei are surrounded by cell walls and organized into cells (the egg apparatus consisting of one egg cell and two synergids,and three antipodal cells).
The remaining two nuclei,known as polar nuclei,are situated below the egg apparatus within a large central cell.
Thus,a typical mature angiospermic embryo sac is $8$-nucleate and $7$-celled.

(B) The statement is False.
In a mature embryo sac,the cells present at the chalazal end are known as antipodal cells.
At the micropylar end,the egg apparatus is present,which consists of two synergids and one egg cell.

(C) The ovule in which the funicle,chalaza,and micropyle lie in one vertical plane is called $Orthotropous$ (Greek: $Orthos$ = straight; $tope$ = turned).
In this type,the body of the ovule is straight.
The hilum and chalaza occur nearly at the same position.
It is also called an $atropous$ or $erect$ ovule,for example,in $Piperaceae$,$Polygonaceae$,and $Urticaceae$.
It is considered the most primitive and simplest type of ovule found in angiosperms.

(D) The provided diagram shows an orthotropous ovule.
In an orthotropous ovule,the micropyle,chalaza,and funicle lie in a single straight vertical line.
This is considered the most primitive type of ovule and is found in members of the family Polygonaceae (e.g.,Polygonum) and Piperaceae.

(C) Filiform apparatus are specialized cellular thickenings found in the synergid cells of the embryo sac.
These structures play a crucial role in guiding the pollen tube into the synergids and facilitating the release of male gametes for fertilization.

(C) Based on the provided diagrams of megasporogenesis:
$A$ points to the cells of the nucellus surrounding the developing megaspore mother cell.
$B$ points to the Megaspore Mother Cell $(MMC)$,which is a large cell with dense cytoplasm.
$C$ points to the nucellus tissue.
$D$ points to the Megaspore dyad,which is formed after the first meiotic division of the $MMC$.
Therefore,the correct labeling is $A-Nucellus, B-MMC, C-Nucellus, D-Megaspore dyad$.
Thus,option $C$ is correct.

(C) -Orthotropous: It is also called atropous. It is erect with no bending,e.g.,$Polygonum$.
$B$-Anatropous: Completely inverted,e.g.,$Helianthus$.
$C$-Hemitropous: The micropyle and chalaza lie at $90^{\circ}$ to the funicle,e.g.,$Ranunculus$.
$D$-Campylotropous: More curvature than hemitropous,e.g.,$Capparis$,mustard.
$E$-Amphitropous: Horse-shoe shaped embryo sac,e.g.,$Capsella$.
$F$-Circinotropous: The funicle grows around the ovule,e.g.,$Opuntia$.

(A) The megasporangium in angiosperms is commonly referred to as the $Ovule$.
It consists of a central mass of tissue called the nucellus,which is protected by one or two protective envelopes known as integuments.
Therefore,an integumented megasporangium is technically defined as an $Ovule$.

(A) The $Nucellus$ is the central part of the ovule consisting of a mass of parenchymatous cells enclosed within the integuments. It serves as the primary nutritive tissue that provides essential nutrients to the developing embryo sac.

(A) In most flowering plants (angiosperms),a single megaspore mother cell undergoes meiosis to produce four megaspores. Out of these,three degenerate,and only one functional megaspore develops into a single embryo sac (also known as the female gametophyte). Therefore,the number of embryo sac in an ovule is generally one.

(C) The nucellus is a mass of diploid $(2n)$ cells found within the ovule that provides nutrition to the developing embryo sac.
The female gametophyte,also known as the embryo sac,is formed from the functional megaspore through mitosis and is haploid $(n)$.

(A) mature embryo sac (also known as the female gametophyte) in angiosperms typically undergoes three successive mitotic divisions following the formation of the functional megaspore.
These divisions result in the formation of $8$ nuclei.
Specifically,the mature embryo sac consists of $3$ antipodal cells,$2$ synergids,$1$ egg cell,and $1$ central cell containing $2$ polar nuclei.
While there are $7$ cells in total,the number of nuclei is $8$ ($3$ in the antipodal cells + $2$ in the synergids + $1$ in the egg cell + $2$ polar nuclei in the central cell).

(C) In a mature $7$-celled,$8$-nucleate embryo sac (Polygonum type),the central cell is the largest cell.
It occupies the major portion of the embryo sac and contains two polar nuclei,which later fuse to form a single diploid secondary nucleus.
The other cells,such as the egg cell,synergids,and antipodal cells,are significantly smaller in size compared to the central cell.

(C) In most flowering plants,the functional megaspore undergoes $3$ successive free-nuclear mitotic divisions to form an $8$-nucleate embryo sac.
These divisions are:
$1$. First mitotic division produces $2$ nuclei.
$2$. Second mitotic division produces $4$ nuclei.
$3$. Third mitotic division produces $8$ nuclei.
Therefore,a total of $3$ mitotic generations are required.

(C) The figure represents a mature embryo sac (female gametophyte) of an angiosperm.
- Part $a$ points to the finger-like projections at the micropylar end of the synergids,known as the filiform apparatus.
- Part $b$ points to the two synergids located at the micropylar end.
- Part $c$ points to the two polar nuclei located in the central cell.
- Part $d$ points to the three antipodal cells located at the chalazal end.
Therefore,the correct sequence is $a$: Filiform apparatus,$b$: Synergids,$c$: Polar nuclei,$d$: Antipodal cells. This matches option $C$.

(A) In the mature embryo sac,the synergids are characterized by the presence of a large vacuole at the chalazal end and a filiform apparatus at the micropylar end.
This specific arrangement of organelles and vacuoles creates a distinct polarity within the synergid cell.
The egg cell,conversely,has a large vacuole at the micropylar end and the nucleus at the chalazal end.
Therefore,the polarity of the synergid cytoplasm is indeed opposite to that of the egg cell.
Both the Assertion and the Reason are correct,and the Reason explains why the synergid has a specific polarity.

(A) An anatropous ovule is the most common type of ovule in angiosperms,occurring in more than $80\%$ of families.
In an anatropous ovule,the body of the ovule becomes completely inverted during development,resulting in the micropyle and the funicle being located side-by-side.
Because of this $180^{\circ}$ rotation (inversion),it is also known as a resupinate ovule.
The hilum and the micropyle are brought close to each other due to this curvature.
Therefore,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for the Assertion.

(B) typical mature angiosperm embryo sac (Polygonum type) is $8$-nucleate and $7$-celled.
It consists of:
$1$. Three antipodal cells at the chalazal end.
$2$. Two synergids and one egg cell (egg apparatus) at the micropylar end.
$3$. One large central cell containing two polar nuclei,which later fuse to form a single diploid secondary nucleus.
Thus,there are $8$ nuclei in total,but they are organized into $7$ cells.

(B) In a typical angiosperm,the mature embryo sac (female gametophyte) is $7$-celled and $8$-nucleated.
It consists of:
$1$. Three antipodal cells at the chalazal end.
$2$. Two synergids and one egg cell at the micropylar end (forming the egg apparatus).
$3$. One central cell containing two polar nuclei.
Thus,there are $7$ cells in total,but because the central cell contains two nuclei,there are $8$ nuclei in total.

(B) The gynoecium (pistil) is the female reproductive part of a flower.
It consists of three main parts:
$1$. Ovary: The basal, swollen part of the pistil.
$2$. Style: The elongated, slender part that connects the ovary to the stigma.
$3$. Stigma: The apical, receptive surface for pollen grains.
Therefore, the sequence from the basal (bottom) to the apical (top) region is $Ovary \rightarrow Style \rightarrow Stigma$.

(B) In angiosperms,the ovule is the structure that develops into a seed after fertilization.
Botanically,the ovule is defined as the integumented megasporangium.
Therefore,an ovule is equivalent to a megasporangium.

(D) The flower consists of four whorls: Calyx,Corolla,Androecium,and Gynoecium.
$1$. The Calyx $(A)$ and Corolla $(B)$ are accessory whorls.
$2$. The Androecium $(C)$ is the male reproductive whorl,which produces pollen grains (male gametes).
$3$. The Gynoecium $(D)$ is the female reproductive whorl,also known as the pistil or carpel,which produces the ovules containing the female gamete (egg cell).
Therefore,the Gynoecium is responsible for producing the female gamete.

(C) The pistil (or gynoecium) 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 stalk that connects the stigma to the ovary.
$3$. $Ovary$: The enlarged basal part containing the ovules.
Anther is a part of the stamen, which is the male reproductive organ of the flower. Therefore, the anther is not a part of the pistil.

(A) The pistil (gynoecium) consists of three main parts:
$1$. $P$ (Stigma): It acts as a receptive surface for pollen grains.
$2$. $Q$ (Style): It is the elongated slender part beneath the stigma.
$3$. $R$ (Ovary): It is the basal swollen part of the pistil that contains the ovules.
Therefore,the correct sequence is $P = \text{Stigma}$,$Q = \text{Style}$,$R = \text{Ovary}$.

(B) In flowering plants, the placenta is located inside the ovarian cavity. The megasporangium, commonly known as the ovule, develops from this placenta. Within the megasporangium, the megaspore mother cell undergoes meiosis to produce megaspores. Therefore, the structure that arises from the placenta is the megasporangium (ovule).

(C) The number of ovules in an ovary varies among different plant species.
$P$ (One ovule in an ovary): Examples include wheat,paddy (rice),and mango.
$Q$ (Many ovules in an ovary): Examples include papaya,watermelon,and orchids.
Therefore,the correct classification is $P$: Wheat,Paddy,Mango and $Q$: Papaya,Watermelon,Orchid. This corresponds to option $C$.

(B) The ovule is a small structure attached to the placenta by means of a stalk called the funiculus. The point of attachment of the body of the ovule with the funiculus is known as the hilum. Thus,the funiculus acts as the stalk that connects the ovule to the placenta.

(A) The ovule is attached to the placenta by means of a stalk called the funicle. The point of attachment of the body of the ovule to the funicle is known as the hilum. Thus,the hilum represents the junction between the ovule and the funicle.

(B) In an angiosperm ovule,the $nucellus$ is the central mass of tissue that contains the embryo sac.
This $nucellus$ is protected by one or two protective envelopes known as $integuments$.
These $integuments$ surround the $nucellus$ except at the tip where a small opening called the $micropyle$ is present.

(C) In the given diagram of an anatropous ovule:
$P$ represents the Funicle,which is the stalk that attaches the ovule to the placenta.
$Q$ represents the Nucellus,which is the central mass of parenchymatous tissue protected by integuments.
$R$ represents the Embryo sac (female gametophyte),which is located within the nucellus.
Therefore,the correct sequence is $P$ = Funicle,$Q$ = Nucellus,$R$ = Embryo sac.

(C) The process of embryo sac formation (megagametogenesis) begins with a cell of the nucellus.
$1$. $A$ specific cell in the nucellus differentiates into the Megaspore Mother Cell $(MMC)$.
$2$. The $MMC$ undergoes meiosis to produce four haploid megaspores.
$3$. Usually,three megaspores degenerate,and one functional megaspore develops into the embryo sac (female gametophyte) through mitosis.
Therefore,the correct sequence is: Nucellar cell $\rightarrow$ Megaspore mother cell $\rightarrow$ Megaspore $\rightarrow$ Embryo sac.

(D) $1$. Megaspore: Formed after meiosis,hence it is haploid $(n)$.
$2$. Megaspore Mother Cell $(MMC)$: $A$ diploid cell $(2n)$ that undergoes meiosis.
$3$. Integument cell: Part of the ovule wall,hence diploid $(2n)$.
$4$. Nucellus cell: Part of the ovule tissue,hence diploid $(2n)$.
$5$. Egg cell: Part of the embryo sac,formed after mitosis,hence haploid $(n)$.
$6$. Antipodal cell: Part of the embryo sac,hence haploid $(n)$.
$7$. Synergid cell: Part of the embryo sac,hence haploid $(n)$.
Therefore,the sequence is $n, 2n, 2n, 2n, n, n, n$.

(B) $1$. The Megaspore Mother Cell $(MMC)$ is a large cell containing dense cytoplasm and a prominent nucleus.
$2$. It differentiates from a cell of the nucellus in the micropylar region of the ovule.
$3$. Since the nucellus is composed of diploid $(2n)$ cells,the $MMC$ is also diploid $(2n)$.
$4$. The $MMC$ undergoes meiosis (reduction division) to produce four haploid $(n)$ megaspores.
$5$. Therefore,the statement that the $MMC$ is haploid is incorrect.