Pteridophytes (General) Questions in English

(A) Circinate venation (or circinate ptyxis) is a unique developmental pattern in ferns where the young leaves (fronds) are coiled like a watch spring,with the apex located at the center of the coil.
This coiling mechanism serves to protect the delicate growing tip of the frond as it develops.

(D) The gametophyte of a fern is a free-living,photosynthetic,thalloid structure known as the prothallus.
It lacks true roots,stems,and leaves,but possesses unicellular rhizoids for anchorage.
The prothallus is monoecious (hermaphroditic) and bears both male sex organs,called antheridia,and female sex organs,called archegonia,on its ventral (under) surface.

(C) In $Pteridophytes$,the xylem lacks vessels (trachea) and the phloem lacks companion cells.
$1$. $Xylem$ in $Pteridophytes$ consists mainly of tracheids,and vessels are generally absent (except in some genera like $Selaginella$ and $Equisetum$ where they are present).
$2$. $Phloem$ in $Pteridophytes$ consists of sieve cells and phloem parenchyma,but companion cells are characteristically absent.
Therefore,the correct option is $(c)$.

(A) $Equisetum$ is commonly known as horse-tail.
It belongs to the class $Sphenopsida$ of the division $Pteridophyta$.
The stem of $Equisetum$ is jointed and ribbed,which gives it a characteristic appearance resembling a horse's tail,hence the name.

(A) Ferns belong to the group Pteridophyta.
$A$ characteristic feature of fern leaves (fronds) is 'circinate vernation',where the young leaves are coiled like a watch spring.
Reticulate and parallel venation are characteristics typically associated with Angiosperms (flowering plants).

(B) Rhynia is considered one of the most primitive vascular plants (Pteridophytes).
It is an extinct genus that lacked true roots and leaves,possessing only a rhizome with rhizoids for anchorage and absorption.

(A) In $Pteridophytes$,specifically in ferns,the spore germinates to produce a small,inconspicuous,multicellular,free-living,mostly photosynthetic thalloid gametophyte called a $prothallus$.
This $prothallus$ requires cool,damp,and shady places to grow.
Therefore,the $prothallus$ stage is a characteristic feature of the life cycle of ferns.

(C) In ferns,the sporangium consists of a specialized layer of cells called the annulus and a thin-walled region known as the stomium.
When the sporangium matures,the annulus cells lose water and contract,creating tension that causes the sporangium to rupture at the stomium.
This mechanism facilitates the explosive dispersal of spores into the environment.
Therefore,both the annulus and the stomium are essential for the disposal of spores.

(C) In heterosporous ferns,the megaspore germinates to form the female gametophyte.
This female gametophyte is typically reduced in size and remains dependent on the parent sporophyte for nutrition.
In many pteridophytes,the gametophyte is referred to as a $Prothallus$,which is a small,multicellular,free-living,mostly photosynthetic thalloid structure.
Therefore,the female gametophyte in these plants is the $Prothallus$.

(D) The plant described possesses vascular tissues ($xylem$ and $phloem$),which excludes $Thallophyta$ and $Bryophyta$ as they are non-vascular plants.
Since the plant reproduces by spores and lacks ovules (and thus lacks seeds),it cannot be a $Gymnosperm$ or $Angiosperm$.
$Pteridophytes$ are the first group of land plants to possess vascular tissues and they reproduce via spores,making them the correct classification.

(A) Ferns belong to the group $Pteridophyta$.
In these plants,the male gametes (antherozoids) are flagellated and motile.
They require a film of water to swim from the antheridium to the archegonium to reach the female gamete (egg).
Therefore,water is essential for the process of fertilization in ferns.

(B) fern prothallus is a heart-shaped,photosynthetic,independent gametophyte that is bisexual,meaning it produces both male $(antheridia)$ and female $(archegonia)$ sex organs.
When fertilization occurs between the gametes (sperm and egg) produced by the same prothallus,it is referred to as self-fertilization or autogamy.
Since the gametes originate from the same individual,this process is a form of self-fertilization.

(D) The monoecious condition refers to the presence of both male and female reproductive structures on the same individual plant or gametophyte.
In $Pteridium$ (a fern),the prothallus (gametophyte) is monoecious,meaning it bears both antheridia (male sex organs) and archegonia (female sex organs) on the same thallus.
$Cycas$ is dioecious.
$Selaginella$ is monoecious but produces different types of spores (heterosporous).
$Pinus$ is monoecious,but the question typically refers to the gametophytic condition in the context of pteridophytes. Given the options,$Pteridium$ is the classic example of a monoecious gametophyte.

$(D)$ The correct answer is $(d)$. In ferns $(Pteris)$, a distinct heteromorphic alternation of generation is observed. This involves the alternation between a dominant, independent, diploid sporophytic phase $(2n)$ and a small, independent, haploid gametophytic phase $(n)$.

(C) The correct answer is $C$. In $Dryopteris$ (a fern),the antheridium produces numerous antherozoids. Each antherozoid is large,uninucleate,spirally coiled,and multiflagellate (possessing many flagella). In contrast,bryophytes like $Funaria$ and $Riccia$ typically produce biflagellate antherozoids.

(A) Heterospory is the production of two different types of spores,microspores and megaspores.
$Selaginella$,$Marsilea$,and $Pinus$ are heterosporous plants.
$Dryopteris$ is a homosporous fern,meaning it produces only one type of spore.
Therefore,the correct option is $A$.

(C) The correct answer is $C$. Ferns,such as $Pteris$ $(Dryopteris)$,exhibit a diplohaplontic life cycle characterized by heteromorphic alternation of generations.
In this life cycle,the sporophytic phase (diploid) and the gametophytic phase (haploid) are morphologically,functionally,and cytologically distinct.
These two generations occur in an alternate manner due to the processes of meiosis (which produces spores) and fertilization (which restores the diploid state).

(A) The stem of $Pteridium$ (specifically $Pteridium$ $aquilinum$) exhibits a complex vascular arrangement known as a polycyclic dictyostele.
In this structure, the vascular tissue is organized into two or more concentric rings of meristeles, which is a characteristic feature of this fern genus.

(C) In $Dryopteris$,the placenta refers to the specialized tissue on the leaf surface (or receptacle) from which the sporangia arise. The indusium,which covers the sorus,also originates from this placental tissue. Therefore,the placenta is the site of attachment for the sporangia.

(B) In $Dryopteris$,the sori are located on the lower surface of the fertile fronds. The lower surface of a leaf is referred to as the abaxial surface. Therefore,the sori in $Dryopteris$ are borne abaxially.

(B) In $Pteridophytes$ like $Dryopteris$,the main plant body is a sporophyte $(2n)$.
Inside the sporangium,specialized cells called spore mother cells $(2n)$ undergo meiosis (reduction division) to produce haploid $(n)$ spores.
These spores germinate to form the prothallus (gametophyte).
Therefore,meiosis occurs at the time of spore formation.

(C) $Dryopteris$ is a genus of ferns belonging to the class $Pteridopsida$.
In ferns,the male gametes,known as antherozoids,are typically multiflagellate and spirally coiled.
These flagella help the antherozoids swim through a film of water to reach the archegonia for fertilization.
Therefore,the correct description for the antherozoids of $Dryopteris$ is that they are multiflagellate and spirally coiled.

(A) In $Dryopteris$,the sporangium wall is differentiated into a specialized region called the $Annulus$.
This region consists of cells that develop a characteristic thickening along their radial and inner tangential walls.
Due to the differential drying of these cells,the $Annulus$ acts as a mechanical device that controls the dehiscence (opening) of the sporangium to release the spores.

(B) $Dryopteris$ is a member of the Pteridophyta group.
In Pteridophytes,the male gametes (antherozoids) are flagellated or ciliated,which allows them to swim in a film of water to reach the female gamete (egg) inside the archegonium.
This requirement for water for fertilization is a primitive trait inherited from aquatic ancestors,even though $Dryopteris$ is a terrestrial plant.
Therefore,the presence of ciliated antherozoids is a clear indication of their aquatic ancestry.

(A) The neck of the archegonium in $Dryopteris$ is composed of $4$ vertical rows of cells.
It encloses a single neck canal cell,which is binucleated (contains two nuclei).

(C) The younger parts of the leaves and the rhizome of $Pteris$ are covered by brown,scaly,hair-like structures known as $ramenta$. These structures provide protection to the developing plant parts.

(C) In $Dryopteris$,the sori (clusters of sporangia) are protected by a specialized,kidney-shaped,membranous structure called the $Indusium$.
$Ramentum$ refers to the brown,scaly hairs on the rhizome.
$Placenta$ is the tissue to which sporangia are attached.
$Sporophyll$ is a leaf that bears sporangia.

(D) In $Dryopteris$,the spores are produced within specialized structures known as sporangia.
These sporangia are typically grouped together in clusters called sori,which are located on the underside of the leaves (sporophylls).
Therefore,the actual site of spore formation is the sporangium.

(B) The correct answer is $B$. In $Dryopteris$,the antherozoids are spirally coiled and multiflagellate,not sickle-shaped. Mature archegonia secrete malic acid to attract antherozoids. The archegonia possess a single binucleate neck canal cell,and the antheridia are typically found on the ventral surface of the prothallus.

(A) $Dryopteris$ is commonly known as the 'male shield fern'.
This name is derived from the fact that its $sori$ (clusters of sporangia) are kidney-shaped and are protected by a shield-like structure called an $indusium$.

(C) The sorus in $Dryopteris$ is a mixed sorus.
In a mixed sorus,sporangia of different ages are present together in an irregular or indefinite arrangement,rather than being arranged in a specific sequence of development.

(B) In $Dryopteris$ $filix-max$,the vascular tissue arrangement in the rachis is characteristic. The meristeles are arranged in a horse-shoe or '$C$' shaped pattern. This specific arrangement is observed in the young rachis of the fern plant.

(B) In $Pteris$ (a fern),the zygote develops into an embryo which remains attached to the gametophyte (prothallus) for nutrition during its early developmental stages.
As the sporophyte grows and develops its own roots,stem,and leaves,it becomes photosynthetically active and independent of the gametophyte.
Therefore,the sporophyte is dependent upon the gametophyte only in the beginning.

(A) Most of the pteridophytes,including the genus $Dryopteris$,produce only one type of spore. This condition is known as homospory. Therefore,$Dryopteris$ is a homosporous fern.

(B) The correct answer is $(b)$.
In $Dryopteris$,the development of the sporangium is of the $Leptosporangiate$ type.
In this type,the sporangium develops from a single superficial initial cell.
This initial cell divides periclinally to form an outer jacket initial and an inner primary sporogenous cell.

(A) $Dryopteris$ is a pteridophyte.
In the life cycle of pteridophytes,the main plant body is a sporophyte $(2n)$.
Spores are produced within sporangia by the process of meiosis.
Since meiosis is a reduction division,the resulting spores are always haploid $(n)$.

(A) In $Pteris$,the sori are borne in two rows on either side of the median vein of the pinnule,located between the margin and the midrib.
These sori are linear in shape and are described as submarginal.
Therefore,the correct description is that they are continuous and linear.

(B) In the genus $Pteris$,the vascular tissue arrangement within the rachis is organized into a specific form. The stele in the rachis of $Pteris$ is typically described as $V$-shaped or horse shoe-shaped in cross-section. This characteristic vascular structure is a diagnostic feature used in the identification of $Pteris$ species.

(C) In $Pteris$,the embryo develops into a young sporophyte. The first structure formed is the $Foot$,which acts as an absorbing organ. It remains embedded in the prothallus (gametophyte) and absorbs water and essential nutrients from it until the young sporophyte becomes independent.

(A) The root of $Pteridium$ (a fern) exhibits a protostele. The xylem is $diarch$ (having two xylem poles) and $exarch$ (protoxylem is located towards the periphery,while metaxylem is towards the center). There are two phloem groups that alternate with the protoxylem poles.

(C) In $Pteridium$,when the leaves reach maturity,they develop groups of sporangia known as sori on the underside of the fertile pinnae.
These specialized leaves that bear sporangia are referred to as sporophylls.
Therefore,the correct option is $C$.

(C) In the $sorus$ of $Pteridium$,the sporangia are protected by two flap-like appendages.
The outer flap is a modification of the leaf margin and is called the false $indusium$.
The inner flap is a thin,membranous outgrowth of the receptacle and is called the true $indusium$.
Therefore,the correct structure is outer false and inner true.

(D) In $Dryopteris$ (a pteridophyte),the life cycle exhibits alternation of generations.
$1$. The sporophyte is the dominant,diploid phase,which is independent and photosynthetic.
$2$. The gametophyte (prothallus) is a small,haploid,multicellular,and photosynthetic structure that is also independent.
$3$. Since both the sporophyte and the gametophyte are independent,both statements $(b)$ and $(c)$ are correct.
Therefore,the correct option is $(d)$.

(C) In $Dryopteris$,the sporangium consists of a stalk and a capsule.
The capsule wall is composed of a single layer of cells.
The $Annulus$ is a specialized row of cells with thickened radial and inner walls that extends around the capsule.
As the sporangium dries,the water in the $Annulus$ cells evaporates,causing the cells to shrink and pull the capsule open,leading to spore dispersal.
Therefore,the $Annulus$ is the structure responsible for the opening mechanism.

(B) Rhizophores are specialized,elongated,leafless structures found in the genus $Selaginella$. They arise from the stem at the point of branching and grow downwards into the soil to produce adventitious roots. They are considered unique structures because they are neither true roots nor true stems in their developmental origin.

(B) . $A$ flap-like outgrowth is present at the base on the adaxial side,which is called a ligule. It may be fan-shaped,tongue-shaped,or lobed. Such leaves are called ligulate. $Selaginella$ is a pteridophyte that possesses these ligulate leaves.

(D) In $Selaginella$,each microsporangium produces a large number of microspores $(400-1600)$ which are very small,typically $15-50 \mu m$ in diameter.
Conversely,the megasporangium produces only four haploid megaspores,which are significantly larger,measuring $1.5-5.0 \ mm$ in diameter.
Comparing the average diameters ($50 \mu m$ vs $5000 \mu m$),the megaspores are approximately $100$ times larger than the microspores.

(A) The stele of the $Selaginella$ stem is a protostele (specifically a $haplostele$).
It consists of a central core of xylem surrounded by phloem,which is further enclosed by a pericycle.
The xylem is typically $diarch$ and $exarch$ in its arrangement.

(A) Positive geotropic structures are those that grow towards the soil,gravity,and darkness.
The rhizophore of $Selaginella$ is a root-like organ that grows downwards into the soil,exhibiting positive geotropism.