Pteridophytes (General) Questions in English

(C) The male gametes (antherozoids) of $Selaginella$ are $128-256$ in number.
They are biflagellated and sickle-shaped (curved) in structure.
Therefore,the correct option is $C$.

(B) $Selaginella$ is a heterosporous pteridophyte. The male gametes,known as antherozoids,are produced within the antheridium. These antherozoids are biflagellate,meaning they possess two flagella at one end,and they have an elongated,spirally coiled body to facilitate movement in water to reach the female gamete.

(D) Selaginella is heterosporous,meaning it produces two types of spores: $Megaspores$ and $Microspores$.
In contrast,Pteris (fern) is homosporous,meaning it produces only one type of spore.
Therefore,the heterosporous condition is the key character that distinguishes Selaginella from Pteris.

(C) $Selaginella$ is a pteridophyte that exhibits heterospory,which means it produces two different types of spores: microspores and megaspores. This phenomenon is considered a significant evolutionary precursor to the seed habit found in higher plants (spermatophytes). Therefore,heterospory is the key character of evolutionary importance in $Selaginella$.

(B) The correct answer is $B$.
Trabeculated endodermis is a characteristic feature of the stem of $Selaginella$.
In most species of $Selaginella$,the endodermis is not a continuous layer but is interrupted by large intercellular spaces.
These spaces are bridged by elongated,radially arranged endodermal cells known as trabeculae.
These trabeculae help in suspending the stele in the center of the stem and facilitate the movement of water and nutrients.

(A) . $Selaginella$ is primarily found in damp,shaded,and humid environments,not commonly on plains.
$B$. Some species of $Selaginella$ are xerophytic,such as $S. lepidophylla$,$S. pilifera$,and $S. bryopteris$.
$C$. The stem of $Selaginella$ typically exhibits a protostelic vascular arrangement.
$D$. The endodermis in $Selaginella$ is characterized by the presence of trabeculae (bridge-like structures),which are modified endodermal cells.

(A) The ligule in $Selaginella$ consists of three distinct parts: the base,the body,and the lamella.
The basal portion is hemispherical in shape and is known as the $Glossopodium$.
This $Glossopodium$ is typically surrounded by a protective layer called the $Glossopodium$ sheath.

(C) In most species of $Selaginella$,the $strobilus$ (cone) is terminal,meaning the growth of the shoot apex ceases after the formation of the $strobilus$. However,in $S. rupestris$,the apex continues its vegetative growth even after the formation of the $strobilus$,resulting in the $strobilus$ appearing lateral rather than terminal. Therefore,the correct option is $C$.

(A) In the male gametophyte of $Selaginella$,the microspore undergoes the first division to form a small prothallial cell and a large antheridial cell.
Therefore,there is only $1$ prothallial cell present in the male gametophyte of $Selaginella$.

(C) The stem of $Selaginella$ exhibits a $Protostele$ type of vascular organization.
In many species of $Selaginella$,the stele is a $Haplostele$ (a simple type of $Protostele$),while in some species,it may be an $Actinostele$ or $Plectostele$.
$Siphonostele$ is characterized by the presence of a central pith,which is absent in the stem of $Selaginella$.

(B) In $Selaginella$,the leaves are small (microphylls) and possess a small,scale-like,membranous outgrowth on their adaxial (upper) surface near the base. This structure is known as a $Ligule$. Therefore,the correct option is $B$.

(C) The rhizophore of $Selaginella$ is a root-like organ that exhibits a simple vascular structure. It contains a single protoxylem element,which is characteristic of a monarch stele.

(B) $Selaginella$ is a heterosporous pteridophyte belonging to the class $Lycopsida$.
One of the most distinct morphological features of $Selaginella$ is the presence of a small,scale-like outgrowth on the upper surface of the leaf near the base,known as a $Ligule$.
Therefore,$Selaginella$ is often referred to as a $ligulate$ pteridophyte.

(C) The most accepted view is that rhizophores are organs $sui \, generis$,which means they are new organs of independent origin $(Bower, 1908; Goebel, 1905)$ or specialized organs meant for bearing roots $(Sporne, 1975)$.

(D) Both $Selaginella$ and ferns belong to the group $Pteridophytes$.
$Pteridophytes$ are vascular cryptogams that reproduce by spores.
They do not produce seeds,which means they lack ovules and seeds.
Therefore,the absence of an ovule is a common character between them.

(B) The correct answer is $B$.
In $Selaginella$,the reproductive structures are organized into compact,cone-like structures known as strobili or spikes.
Each strobilus consists of numerous ligulate sporophylls arranged in a cluster.
These sporophylls bear sporangia on their upper surfaces.
$Selaginella$ is heterosporous,meaning it produces two types of sporangia: $(i)$ Microsporangia,which produce microspores,and $(ii)$ Megasporangia,which produce megaspores.
Both types of sporangia are typically found within the same strobilus.

(A) The rhizophore in $Selaginella$ is exogenous in origin.
It is a leafless,colorless,positively geotropic structure that arises from the stem at the point of branching.
It lacks root caps and root hairs.
Upon touching the soil,it produces adventitious roots at its apex.

(A) In $Selaginella$,the development of the embryo is $exoscopic$.
During the initial stages of development,the zygote undergoes a transverse division to form an upper (epibasal) cell and a lower (hypobasal) cell.
The embryo development is $meroblastic$ because only a part of the zygote contributes to the formation of the embryo proper,while the other part forms the suspensor.

(C) In $Selaginella$,the development of the gametophyte is precocious,meaning it begins while the spore is still within the sporangium.
Specifically,the megagametophyte develops within the walls of the megaspore.
When the megaspore containing the female gametophyte is exposed to light through the tri-radiate ridge,it develops chlorophyll in the cushion region,but the primary characteristic defining its development is that it remains enclosed within the megaspore wall.

(B) In $Selaginella$, the megaspore mother cell undergoes meiosis to produce four megaspores.
However, in $Selaginella rupestris$, not all four megaspores are functional.
Specifically, only two of the four megaspores are functional, while the others degenerate.
Therefore, the correct number of functional megaspores in $Selaginella rupestris$ is $2$.

(B) In $Selaginella$,the sporangium develops from a group of initial cells. The central cells of the sporangium differentiate into the sporogenous tissue,while the peripheral cells form the wall of the sporangium. The tapetum is formed from the innermost layer of the sporangial wall or from the peripheral cells of the sporogenous tissue. In $Selaginella$,it is specifically derived from the sporogenous tissue.

(D) $Selaginella$ exhibits a rudimentary seed habit,which is considered a precursor to the evolution of seeds in higher plants.
This phenomenon is based on several key evolutionary adaptations:
$1$. $Heterospory$: The production of two different types of spores (microspores and megaspores).
$2$. Reduction in the number of megaspores: In $Selaginella$,the number of functional megaspores is significantly reduced,often to a single functional megaspore per megasporangium.
$3$. Retention of the megaspore: The megaspore is retained within the megasporangium (often associated with the cone or strobilus) for a period,allowing for the development of the female gametophyte.
Therefore,all these factors contribute to the seed habit.

(B) $Selaginella$ is a pteridophyte that exhibits heterospory,meaning it produces two distinct types of spores: $megaspores$ and $microspores$.
Additionally,its leaves possess a small,flap-like outgrowth on the adaxial surface at the base,known as a $ligule$. This characteristic is a defining feature of the genus $Selaginella$.

(B) The main plant body of $Selaginella$ $sp.$ is the sporophyte,which is diploid $(2n)$ in condition.
In $Pteridophytes$,the sporophyte is the dominant phase of the life cycle,which is differentiated into true roots,stems,and leaves.

(C) The correct answer is $C$.
In $Selaginella$, the life cycle exhibits heteromorphic alternation of generations.
This means that the sporophytic generation (the diploid plant body) and the gametophytic generation (the haploid plant body) are morphologically and structurally distinct from each other.
$Spirogyra$ and $Mucor$ do not show this type of alternation of generations, and $Pinus$ exhibits a different type of life cycle pattern.

(D) The rhizophore in $Selaginella$ is considered an organ of unique origin. Botanists like Williams, Goebel, and Bower regard it as an intermediate structure between a root and a shoot, hence it is termed an "Organ sui-genesis".

(D) $Selaginella$ is a heterosporous pteridophyte,meaning it produces two types of spores: microspores and megaspores.
Reduction division,also known as meiosis,occurs in the spore mother cells located within the sporangia to produce these haploid spores.
Since both microspores and megaspores are produced via meiosis from their respective mother cells,reduction division occurs during the formation of both.
Therefore,the correct answer is $(d)$.

(A) $Selaginella$ is known as the 'resurrection plant'.
In dry conditions,the plant rolls up into a compact ball to prevent desiccation.
During rainy conditions,the ball absorbs moisture and becomes green and active again.
This unique ability to survive extreme dehydration and revive upon rehydration is why it is called a resurrection plant.

(B) In $Equisetum$,the spores are green because they contain chloroplasts. These spores are also characterized by the presence of four hygroscopic,club-shaped appendages called elaters,which help in spore dispersal.

(C) Heterospory is a condition where two types of spores are produced: microspores and megaspores.
$Selaginella$ is a classic example of a pteridophyte that exhibits heterospory.
The microspores germinate to form the male gametophyte,while the megaspores germinate to form the female gametophyte.

(B) Heterospory is the production of two different types of spores,microspores and megaspores. This phenomenon is a precursor to the seed habit,which is observed in certain Pteridophytes like $Selaginella$. $Selaginella$ is a heterosporous plant that possesses a small,scale-like outgrowth at the base of the leaf called a $Ligule$. The presence of a $Ligule$ is a characteristic feature of the order $Selaginellales$.

(C) The development of a sporophyte directly from the gametophyte without the fusion of gametes (i.e.,without fertilization) is known as $Apogamy$.
In $Selaginella$,when this process occurs from cells of the female gametophyte other than the oosphere (egg cell),it is specifically referred to as $Apogamy$.
$Apospory$ is the reverse process,where a gametophyte develops directly from the sporophyte without meiosis.

(A) The antherozoids (male gametes) of $Selaginella$ are biflagellate.
They possess an elongated,spirally coiled body.
The two flagella are attached at the anterior end of the body.
Therefore,the correct description is an elongated body with two flagella at one end.

(C) In $Selaginella$,the stem exhibits a polystelic condition.
This means the stem contains multiple steles,where each stele consists of a central xylem core surrounded by phloem,which is further enclosed by a pericycle and an endodermis.

(A) $Ramenta$ (scales) are characteristic features found in ferns like $Pteris$ and $Dryopteris$. They are not present in $Selaginella$.
$Trabeculae$ are modified endodermal cells found in the stem of $Selaginella$.
$Rhizophore$ is a unique,root-like organ found in $Selaginella$ that arises from the stem.
$Ligule$ is a small,scale-like outgrowth found on the upper surface of the leaf in $Selaginella$.

(A) Selaginella is a heterosporous pteridophyte belonging to the class Lycopsida.
One of the characteristic features of the leaves of Selaginella is the presence of a small,scale-like outgrowth on the adaxial (upper) surface near the base,which is known as the ligule.
Therefore,the correct answer is $A$ (Ligule).

(B) $Adiantum$ is commonly known as the "Maidenhair fern".
This name is given because of its shining, smooth, and blackish hair-like petioles (stalks) that resemble human hair.

(B) The correct answer is $B$.
In $Selaginella$,the leaves are small and are referred to as microphyllous leaves.
In contrast,larger leaves found in other pteridophytes like ferns are known as megaphyllous leaves.
$Selaginella$ is a classic example of a pteridophyte that exhibits the microphyllous condition.

(A) In ferns,the antheridia (male sex organs) produce motile male gametes known as antherozoids.
These antherozoids are characteristically coiled in shape and possess multiple flagella (multiflagellate) to facilitate movement in water towards the archegonia.
In contrast,some other pteridophytes like $Selaginella$ produce biflagellated antherozoids.

(A) In ferns,the plant body is a sporophyte $(2n)$,which is diploid.
The embryo,including its foot,is a part of the sporophyte generation and is therefore diploid $(2n = 8)$.
Spores are produced by meiosis in the sporangia,making them haploid $(n)$.
Therefore,the number of chromosomes in the spores will be half the number of chromosomes in the embryo.
Calculation: $n = 8 / 2 = 4$.
Thus,the correct option is $A$.

(A) In $Leptosporangiate$ ferns,the entire sporangium develops from a single superficial initial cell.
This initial cell divides periclinally into an outer and an inner component.
The inner cell forms the stalk,while the outer cell gives rise to the sporangium proper.
This type of development is characteristic of most modern ferns (e.g.,$Polypodiaceae$).

(D) The microspore of $Selaginella$ undergoes development to form a $13$-celled male gametophyte.
This structure consists of $1$ prothallial cell,$8$ jacket cells (which form the wall of the antheridium),and $4$ primary androgonial cells (which eventually produce the antherozoids).
Therefore,the correct composition is $1$ prothallial cell $+ 8$ jacket cells $+ 4$ androgonial cells.

(D) In $Selaginella$,the antheridium develops from a single initial cell. The development involves repeated divisions resulting in a large number of androcytes. Each androcyte eventually metamorphoses into a single biflagellate antherozoid. $A$ mature antheridium of $Selaginella$ typically produces a large number of antherozoids,generally ranging from $128$ to $256$.

(B) The endodermis in the $Selaginella$ stem is interrupted by large intercellular spaces.
These elongated,radial,or bridge-like endodermal cells that span the air space are called trabeculae.
Therefore,trabeculae are modified endodermal cells.
This layer is considered the endodermis due to the presence of Casparian strips on these cells.

(C) In pteridophytes,the main plant body is sporophytic. The gametophytic generation is small,inconspicuous,and free-living,which is commonly known as the $Prothallus$. It is typically heart-shaped and photosynthetic.

(D) In the archegonium of ferns (Pteridophytes),the neck canal cells are typically present as a single cell that is often binucleate. This cell is formed by the division of the neck canal initial. Therefore,there is $1$ neck canal cell containing two nuclei.

(D) The correct answer is $(d)$.
At the base of the ligule,there is a sheath of elongated cells known as the glossopodium,which is secretory in nature.
The ligule serves both secretory and protective functions.
It secretes water or mucilage to keep the growing point of the stem and young leaves moist.
Additionally,it protects the young leaves during their development.

(A) Circinate vernation is a characteristic feature of fern leaves,where the young leaves are coiled from the apex to the base like the spring of a watch. This protects the delicate growing tip of the leaf.