Stamen, Microsporangium and Pollen Grain Questions in English

(B) In over $60\%$ of angiosperms,pollen grains are shed at the two-celled stage.
These two cells are the vegetative cell and the generative cell.
The vegetative cell is bigger,has abundant food reserve,and a large irregularly shaped nucleus.
The generative cell is small and floats in the cytoplasm of the vegetative cell.

(A) In angiosperms,the pollen grain undergoes mitotic division to form two cells: a large vegetative cell and a small generative cell.
In about $60\%$ of angiosperms,pollen grains are shed at this $2$-celled stage.
In the remaining species,the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed.
Thus,the $3$-celled stage consists of one vegetative cell and two male gametes.

(A) The tapetum is the innermost layer of the microsporangium wall.
It provides nourishment to the developing pollen grains (microspores).
Cells of the tapetum are characterized by dense cytoplasm and are often multinucleate due to endomitosis or free nuclear division.
This multinucleate condition allows the tapetum to synthesize large amounts of proteins,enzymes,and nutrients required for the rapid development of microspore mother cells.
Therefore,both the Assertion and the Reason are true,and the Reason correctly explains why the tapetum cells possess multiple nuclei.

(B) The exine of the pollen grain is composed of a highly resistant organic material called $Sporopollenin$.
It is one of the most resistant organic materials known.
It can withstand high temperatures,strong acids,and alkali.
No enzyme that degrades $Sporopollenin$ is known so far.
Therefore,pollen grains are well-preserved as fossils due to the presence of $Sporopollenin$.

(C) typical angiosperm anther is bilobed,meaning it has two lobes.
Each lobe is dithecous,meaning it contains two theca (pollen sacs),making a total of four pollen sacs in the anther.
Due to these four pollen sacs,the anther is often described as tetragonal (four-sided) in cross-section.
'Apocarpous' refers to a condition in the gynoecium where carpels are free,not fused. Therefore,it is not a characteristic of an anther.

(C) In angiosperms,the pollen grain represents the male gametophyte.
During its development,the microspore undergoes mitosis to form two cells: a large vegetative cell and a small generative cell.
The generative cell then undergoes a mitotic division to produce two male gametes.
Therefore,the male gametes are formed by the division of the generative cell.

(D) typical angiosperm anther is bilobed,meaning it consists of two lobes.
Each lobe contains two theca,making it dithecous.
Therefore,the anther has four microsporangia located at the corners,two in each lobe,which makes it tetrasporangiate.
Thus,all the given options are correct.

(B) The transverse section of a young anther shows four wall layers surrounding the microsporangia.
$1$. The outermost single layer is the Epidermis $(A)$.
$2$. The layer just below the epidermis is the Endothecium $(B)$.
$3$. The layers internal to the endothecium are the Middle layers $(C)$,which are usually $2-3$ layers thick.
$4$. The innermost layer that nourishes the developing pollen grains is the Tapetum $(D)$.
Therefore,the correct identification is: part-$A \rightarrow$ Epidermis,part-$B \rightarrow$ Endothecium,part-$C \rightarrow$ Middle layers,part-$D \rightarrow$ Tapetum.

(A) Statement-$I$ is correct because flowers are the reproductive organs of angiosperms where sexual reproduction occurs.
Statement-$II$ is correct because a typical angiosperm anther is bilobed (having two lobes),dithecous (each lobe having two theca),and generally appears tetragonal (four-sided) in transverse section,containing four microsporangia.

(A) In angiosperms,the microspore mother cells $(MMC)$ are diploid $(2n)$.
These cells undergo meiosis,which is a reductional division.
As a result of meiosis,each $MMC$ produces four haploid microspores,which are collectively known as a microspore tetrad.
Therefore,the ploidy of the cells of the microspore tetrad is haploid $(n)$.

(C) The developmental sequence of male gametophyte formation in angiosperms is as follows:
$1$. $E$ (Sporogenous tissue): This is the mass of cells present in the microsporangium.
$2$. $B$ (Pollen mother cell): Some cells of the sporogenous tissue differentiate into pollen mother cells ($PMC$s).
$3$. $C$ (Microspore tetrad): Each $PMC$ undergoes meiosis to form a cluster of four haploid microspores,known as a microspore tetrad.
$4$. $A$ (Pollen grain): The microspores separate and develop into pollen grains.
$5$. $D$ (Male gametes): The pollen grain undergoes mitosis to produce two male gametes.
Thus,the correct sequence is $E \rightarrow B \rightarrow C \rightarrow A \rightarrow D$.

(D) typical angiosperm anther is dithecous,meaning it has two lobes. Each lobe contains two pollen sacs (microsporangia),resulting in a total of four pollen sacs in a dithecous anther.

(B) The pollen grain wall consists of two layers: the outer exine and the inner intine.
The exine is made of sporopollenin,which is one of the most resistant organic materials known.
However,the exine is absent at certain places,and these apertures are known as germ pores.
During the process of fertilization,the pollen tube emerges from the pollen grain through one of these germ pores,which is essential for pollen germination and the delivery of male gametes to the ovule.

(B) The anther wall consists of four layers:
$1$. Epidermis: The outermost layer,which provides protection.
$2$. Endothecium: The layer beneath the epidermis,characterized by fibrous thickenings that help in dehiscence.
$3$. Middle layers: These consist of $1-2$ layers of thin-walled cells that often disintegrate in a mature anther.
$4$. Tapetum: The innermost layer,which provides nutrition to the developing pollen grains.
Matching the characteristics:
- $i$. Nutritive layer: $c$. Tapetum
- $ii$. Layer with fibrous thickness: $d$. Endothecium
- $iii$. Protective layer: $a$. Epidermis
- $iv$. Layer that disintegrates in mature anther: $b$. Middle layers
Thus,the correct match is $i-c, ii-d, iii-a, iv-b$.

(B) The wall of a mature anther consists of four layers: epidermis,endothecium,middle layers,and tapetum.
Tapetum is the innermost layer of the anther wall.
It directly surrounds the sporogenous tissue,which consists of microspore mother cells (MMCs).
Therefore,the microspore mother cells are immediately enclosed by the tapetum.

(B) Each pollen mother cell (also known as a microspore mother cell) undergoes a single meiotic division to produce one tetrad of four haploid pollen grains.
Therefore,to form $8$ pollen tetrads,$8$ pollen mother cells are required.

(A) The correct answer is $A$.
The stigma is the receptive part of the carpel (pistil),which is a vegetative organ of the flower,thus representing the sporophytic generation $(2n)$.
The pollen grain is the male gametophyte,which develops from the microspore and represents the gametophytic generation $(n)$.

(D) i. $Dithecous$: $A$ typical angiosperm anther is bilobed,meaning it has two lobes.
ii. $Tetrasporangiate$: Each lobe contains two microsporangia,resulting in a total of four microsporangia in the anther.
iii. Therefore,a typical anther is described as $dithecous$ and $tetrasporangiate$.

(B) In the early development of the anther,a group of hypodermal cells in each corner of the young anther becomes differentiated from the surrounding cells.
These cells are characterized by their dense cytoplasm and prominent nuclei.
These differentiated cells are known as archesporial cells.
Therefore,the archesporial cells are formed from the hypodermal cells of the anther.

(C) Statement $I$ is correct: In angiosperms,a typical anther is bilobed or dithecous,with each lobe containing two thecae (pollen sacs),making it tetrasporangiate.
Statement $II$ is incorrect: The process by which microspores are formed from a pollen mother cell $(PMC)$ through meiosis is called microsporogenesis,not sporogenesis. Sporogenesis is a broader term,and the specific term for pollen formation is microsporogenesis.

(A) One microspore mother cell $(MMC)$ undergoes meiosis to produce $4$ pollen grains.
Each chamber of the anther contains $75$ $MMC$s.
Since the anther is $tetralocular$ (has $4$ chambers),the total number of $MMC$s = $75 \times 4 = 300$.
Total pollen grains produced = $300 \times 4 = 1200$.

(A) In angiosperms,the development of the male gametophyte from a pollen mother cell $(PMC)$ occurs as follows:
$1$. The $PMC$ undergoes meiosis to produce a microspore tetrad (four haploid microspores).
$2$. Each microspore then undergoes two mitotic divisions to form the mature male gametophyte (pollen grain).
$3$. The first mitotic division produces a vegetative cell and a generative cell.
$4$. The second mitotic division occurs in the generative cell to produce two male gametes.
Therefore,the process involves one meiotic division followed by two mitotic divisions.

(B) In angiosperms,the microspore (pollen grain) undergoes the first mitotic division to form a large vegetative cell and a small generative cell.
Subsequently,the generative cell undergoes a second mitotic division to produce two male gametes.
Therefore,the development of male gametes from the microspore involves a total of two mitotic divisions.

(C) The pollen grain wall is composed of two layers: the inner intine and the outer exine.
The exine is the hard outer layer of the pollen grain.
It is composed of $sporopollenin$,which is one of the most resistant organic materials known.
$Sporopollenin$ can withstand high temperatures,strong acids,and alkali,and no enzyme that degrades $sporopollenin$ is known so far.
Therefore,the correct option is $C$.

(A) The pollen tube is an extension of the inner wall of the pollen grain,known as the intine.
The intine is primarily composed of cellulose and pectin.
As the pollen tube grows through the style,its wall maintains this composition to allow for flexibility and elongation during the delivery of male gametes to the ovule.
Sporopollenin is found only in the exine (outer layer) of the pollen grain,not in the pollen tube wall.

(D) The wall of a mature anther consists of four layers: Epidermis, Endothecium, Middle layers, and Tapetum.
$1$. The $Epidermis$ is the outermost protective layer.
$2$. The $Endothecium$ lies just below the epidermis. At maturity, the cells of the endothecium develop fibrous thickenings of cellulose (often referred to as callose or cellulosic bands) which help in the dehiscence of the anther.
$3$. The $Middle$ $layers$ are ephemeral and degenerate at maturity.
$4$. The $Tapetum$ is the innermost layer that provides nourishment to the developing pollen grains.
Therefore, the correct answer is $Endothecium$.

(A) tetralocular anther consists of four pollen chambers.
Since there are $1280$ microspores in the entire anther,the number of microspores in each chamber is $\frac{1280}{4} = 320$.
One microspore mother cell $(MMC)$ undergoes meiosis to form four haploid microspores.
Therefore,the number of $MMCs$ required to produce $320$ microspores is $\frac{320}{4} = 80$.
Thus,$80$ $MMCs$ are present in each pollen chamber.

(D) The anther contains a central mass of cells known as the $sporogenous \text{ tissue}$.
These cells undergo meiosis to form microspore tetrads.
Each microspore eventually develops into a pollen grain.
Therefore,the pollen grains develop from the $sporogenous \text{ tissue}$ of the anther.

(A) The $Tapetum$ is the innermost layer of the microsporangium wall.
It provides nourishment to the developing pollen grains.
Cells of the $Tapetum$ often become multinucleated due to endomitosis (replication of $DNA$ without nuclear division) or cell fusion,which allows them to support the high metabolic demand of developing microspores.

(A) The figure shows a cross-section of a young anther (microsporangium). The wall layers of a typical microsporangium are arranged from the outside to the inside as follows:
$(i)$ Epidermis: The outermost protective layer.
(ii) Endothecium: The layer lying just below the epidermis.
(iii) Middle layers: One to three layers of cells located between the endothecium and the tapetum.
(iv) Tapetum: The innermost nutritive layer that surrounds the sporogenous tissue.
Therefore,the correct sequence is $(i)$ Epidermis,(ii) Endothecium,(iii) Middle layer,(iv) Tapetum. Thus,option $A$ is correct.

(D) The microsporangium is surrounded by four wall layers: the epidermis,endothecium,middle layers,and tapetum.
$1$. The outer three wall layers (epidermis,endothecium,and middle layers) perform the function of protection and help in the dehiscence of the anther to release the pollen.
$2$. The innermost wall layer is the $Tapetum$.
$3$. The $Tapetum$ nourishes the developing pollen grains.
Therefore,the correct option is $D$.

(A) The wall layers of a young anther, starting from the innermost layer (closest to the sporogenous tissue) to the outermost layer (periphery), are arranged as follows:
$1$. $Tapetum$ (innermost layer, surrounding the sporogenous tissue).
$2$. $Middle \text{ } layers$ (located between the tapetum and endothecium).
$3$. $Endothecium$ (located beneath the epidermis).
$4$. $Epidermis$ (the outermost protective layer).
Therefore, the correct sequence from the sporogenous tissue to the periphery is $Tapetum \rightarrow Middle \text{ } layers \rightarrow Endothecium \rightarrow Epidermis$.

(A) The correct answer is $A$. In a mature pollen grain,there are two cells: the vegetative cell and the generative cell. The generative cell later divides to form two male gametes. Therefore,stating that it contains a 'male gamete' instead of a 'generative cell' is incorrect. Option $B$ is correct as pollen grains are generally spherical measuring $25-50 \ \mu m$. Option $C$ is correct as the exine layer has germ pores where sporopollenin is absent. Option $D$ is correct as the exine is composed of the highly resistant organic material,sporopollenin.

(A) The outer layer of the pollen grain,known as the exine,is made up of a highly resistant organic material called sporopollenin.
Sporopollenin is one of the most resistant organic materials known; it can withstand high temperatures,strong acids,and alkali conditions.
No enzyme that degrades sporopollenin is known.
Due to the presence of this substance,pollen grains are well-preserved as fossils.
Therefore,both Assertion $A$ and Reason $R$ are correct,and Reason $R$ is the correct explanation for Assertion $A$.

(D) The exine of pollen grains is made up of a highly resistant organic material called $Sporopollenin$.
$Sporopollenin$ is one of the most resistant organic materials known.
It can withstand high temperatures,strong acids,and alkali conditions.
No enzyme that degrades $Sporopollenin$ is known to date.
Due to this characteristic,pollen grains are well preserved as fossils.

(D) Each stamen has a bilobed,dithecous anther,which means it contains $4$ microsporangia.
Total number of microsporangia in $10$ stamens = $10 \times 4 = 40$.
Each microsporangium contains $5$ pollen mother cells (PMCs).
Total number of PMCs in the flower = $40 \times 5 = 200$.
Each pollen mother cell undergoes meiosis to produce $4$ pollen grains.
Total number of pollen grains = $200 \times 4 = 800$.

(B) The stamen is the male reproductive organ of a flower,consisting of two main parts: the anther and the filament.
$1$. The anther is the pollen-bearing part.
$2$. The filament is the long,slender stalk that supports the anther.
Therefore,the stalk of the stamen is the filament.

(B) The correct answer is $B$.
$Statement \ 1$ is correct because the microsporangium is surrounded by four wall layers: epidermis, endothecium, middle layers, and the innermost layer, which is the tapetum.
$Statement \ 2$ is correct because the cells of the tapetum possess dense cytoplasm and generally have more than one nucleus (multinucleate condition). Their primary function is to provide nourishment to the developing pollen grains.

(B) typical angiosperm anther is bilobed,with each lobe having two theca (dithecous).
In a transverse section,a typical microsporangium appears near-circular in outline.
It is generally surrounded by four wall layers: epidermis,endothecium,middle layers,and tapetum.
There are four microsporangia located at the corners,two in each lobe.
Eventually,these microsporangia develop into pollen sacs and extend longitudinally all through the length of an anther and are packed with pollen grains.

(D) The exine of pollen grains is highly resistant to enzyme action.
Pollen grains possess a prominent two-layered wall. The hard outer layer,known as the exine,is composed of sporopollenin,which is one of the most resistant organic materials known to science.
It can withstand high temperatures,strong acids,and strong alkalis.
To date,no enzyme has been discovered that can degrade sporopollenin. This unique chemical property allows pollen grains to be well-preserved as fossils over long periods.

(A) The correct answer is $A$.
In angiosperms,the pollen grain can be shed at either the $2$-celled stage or the $3$-celled stage.
At the $3$-celled stage,the generative cell undergoes mitosis to form two male gametes.
Therefore,the pollen grain contains one large vegetative cell (tube cell) and two male gametes.

(C) Statement $I$ is correct: In approximately $40\%$ of angiosperms, the generative cell divides mitotically to form two male gametes before the pollen grains are shed, resulting in a $3$-celled stage. In the remaining $60\%$ of species, pollen grains are shed at the $2$-celled stage.
Statement $II$ is incorrect: The inner wall of the pollen grain is called the intine. It is a thin and continuous layer made up of cellulose and pectin. It is not discontinuous; rather, the exine (outer layer) is discontinuous at the germ pores.

(A) The correct answer is $A$.
Pollen grains are unicellular,haploid,and generally spherical in shape.
They typically measure about $25-50 \ \mu m$ (micrometres) in diameter.

(C) dithecous anther consists of $4$ pollen sacs (microsporangia).
Each $MMC$ (Microspore Mother Cell) undergoes meiosis to produce $4$ haploid microspores (pollen grains).
Number of $MMC$ per pollen sac = $1000$.
Number of pollen grains per pollen sac = $1000 \times 4 = 4000$.
Since there are $4$ pollen sacs in a dithecous anther,the total number of pollen grains = $4 \times 4000 = 16000$.

(C) The correct answer is $C$.
In a mature pollen grain,the outer protective layer is known as the exine,which is composed of a highly resistant organic material called sporopollenin.
However,at certain specific locations,the exine is absent or very thin,and these regions lack sporopollenin.
These specific regions are termed as germ pores.
During the process of pollen germination,the pollen tube emerges from the pollen grain through these germ pores.

(A) Based on the $T.S.$ of anther diagram:
$A$ points to the central region connecting the two lobes,which is the Connective tissue.
$B$ points to the layer just inside the epidermis,which is the Endothecium.
$C$ points to the microspores or Pollen grains located within the microsporangium.
Therefore,the correct identification is $A$-Connective tissue,$B$-Endothecium,$C$-Pollen grain. The correct option is $A$.

(B) exine of pollen grain.
Sporopollenin,found in the exine of pollen grains,is one of the most resistant organic materials known. It is highly resistant to extreme temperatures,strong acids,and alkali,and no enzyme that degrades sporopollenin is known so far. In contrast,the intine of pollen grains is composed of cellulose and pectin. The endothecium of the anther aids in dehiscence,while the tapetum provides nourishment to the developing pollen grains.

(D) The process of microsporogenesis occurs in the following sequence:
$1$. The primary sporogenous tissue $(B)$ undergoes mitotic divisions to form pollen mother cells $(D)$.
$2$. Each pollen mother cell $(D)$ undergoes meiosis to form a group of four haploid cells known as microspore tetrads $(A)$.
$3$. These microspores separate and mature into pollen grains $(C)$.
Therefore,the correct sequence is $B \rightarrow D \rightarrow A \rightarrow C$.