Internal structure of stem Questions in English

(D) In dicot stems,the innermost layer of the cortex is called the endodermis.
The cells of the endodermis are rich in starch grains,and this layer is therefore referred to as the starch sheath.
Since the presence of starch grains is the reason why it is called the starch sheath,Statement-$2$ provides the correct explanation for Statement-$1$.
Therefore,both statements are true and Statement-$2$ is the correct explanation of Statement-$1$.

(B) Bicollateral vascular bundles are a type of conjoint vascular bundle where the phloem is present on both the outer and inner sides of the xylem. These are characteristic of the family $Cucurbitaceae$. In these bundles,two patches of phloem are present,one towards the periphery and one towards the center,separated by xylem.

(A) In the stem,the protoxylem lies towards the center (pith) and the metaxylem lies towards the periphery of the organ. This arrangement of primary xylem is called $Endarch$.
In contrast,in the roots,the protoxylem lies towards the periphery and the metaxylem lies towards the center. This arrangement is called $Exarch$.
Therefore,the characteristic feature of the stem is the $Endarch$ condition.

(A) The characteristics described,such as scattered vascular bundles in the ground tissue and the presence of a sclerenchymatous bundle sheath around each vascular bundle,are typical features of $Monocot$ stems.
Among the given options,$Maize$ ($Zea$ $mays$) is a $Monocot$ plant.
In contrast,$Sunflower$,$Gram$,and $Banyan$ are $Dicot$ plants,which typically have vascular bundles arranged in a ring.

(A) In the stem of $Cucurbita$ (a member of the $Cucurbitaceae$ family),the vascular bundles are arranged in a specific manner.
They are described as $Bicollateral$ because the phloem is present on both the outer and inner sides of the xylem.
They are also $Open$ because a strip of cambium is present between the xylem and phloem,allowing for secondary growth.
Therefore,the correct description is $Bicollateral$ and $Open$.

(A) In monocot stems like wheat,the hypodermis is composed of sclerenchyma cells,which provide mechanical strength and are referred to as a hard hypodermis.
In dicot stems like sunflower,the hypodermis is composed of collenchyma cells,which provide flexibility and are referred to as a soft hypodermis.
Roots generally do not possess a hypodermis.
Therefore,the correct answer is wheat stem.

(D) In plants,vascular bundles are classified as open or closed based on the presence or absence of cambium.
In dicotyledonous stems,vascular bundles contain cambium between the xylem and phloem,which allows for secondary growth; these are called open vascular bundles.
In monocotyledonous stems,the cambium is absent between the xylem and phloem,meaning they cannot undergo secondary growth.
Therefore,vascular bundles in monocotyledons are referred to as closed vascular bundles.

(B) In monocot stems like $maize$ ($Zea$ $mays$),the vascular bundles are conjoint,collateral,and closed. $A$ characteristic feature of these vascular bundles is the presence of a lysigenous water-containing cavity (also known as a protoxylem lacuna or lysigenous cavity) formed by the disintegration of the protoxylem elements and the surrounding parenchyma cells during the growth of the stem.

(C) : Vascular bundles consist of complex tissues,the phloem and xylem. In dicots,cambium is present between the xylem and phloem,which helps in secondary growth; this type of vascular bundle is called open. In monocots,cambium is absent,so these are called closed vascular bundles.

(A) $Barley$ is a monocotyledonous plant.
In monocot stems,the vascular bundles are conjoint,collateral,and closed because the cambium is absent.
These vascular bundles are scattered throughout the ground tissue.

(B) In monocotyledonous stems,the vascular bundles are scattered in the ground tissue.
Each vascular bundle is conjoint,collateral,and closed.
These vascular bundles are surrounded by a sclerenchymatous bundle sheath,which provides mechanical support to the stem.

(A) In the anatomy of a dicot stem,the cortex is divided into three sub-zones: the hypodermis,the cortical layers,and the innermost layer known as the endodermis.
The cells of the endodermis are rich in starch grains,which is why this layer is frequently referred to as the starch sheath.
Therefore,the correct option is $A$.

(D) The correct matches are as follows:
$(1)$ Monocot stem: Vascular bundles are conjoint and closed $(d)$.
$(2)$ Monocot root: Typically exhibits polyarch xylem bundles $(c)$.
$(3)$ Monocot leaf: Contains bulliform cells $(a)$ which help in leaf rolling to minimize water loss.
Therefore,the correct matching is $(1-d), (2-c), (3-a)$.

(B) In a dicot stem, the innermost layer of the cortex is known as the $Endodermis$.
This layer is composed of barrel-shaped cells and is rich in starch grains.
Due to the presence of abundant starch, the $Endodermis$ in the dicot stem is often referred to as the $Starch \text{ } sheath$.

(A) In monocot stems,the vascular bundles are scattered in the ground tissue.
Each vascular bundle is conjoint,meaning both xylem and phloem are present in the same bundle.
They are closed,which means there is no cambium present between the xylem and phloem,preventing secondary growth.
Therefore,the correct description for monocot stem vascular bundles is conjoint and closed.

(A) In plants,vascular bundles are classified as open or closed based on the presence or absence of cambium.
Open vascular bundles contain cambium between the xylem and phloem,which allows for secondary growth,and are characteristic of dicotyledons.
Closed vascular bundles lack cambium between the xylem and phloem,meaning they cannot undergo secondary growth,which is a characteristic feature of monocotyledons.
Therefore,the correct reason is that cambium is absent.

(A) In a $Monocot$ stem,the ground tissue consists of a mass of parenchyma cells with no clear differentiation into hypodermis,cortex,endodermis,pericycle,and pith. The vascular bundles are scattered throughout the ground tissue. In contrast,$Dicot$ stems and roots show clear differentiation of the cortex into various zones like hypodermis,general cortex,and endodermis.

(B) Maize $(Zea \ mays)$ is a monocotyledonous plant.
In monocot stems,the vascular bundles are numerous,scattered throughout the ground tissue,and are surrounded by a sclerenchymatous bundle sheath.
Each vascular bundle is 'closed',meaning it lacks a cambium between the xylem and phloem,which prevents secondary growth.
Therefore,the vascular bundles in a maize stem are closed and scattered.

(C) In dicot stems and roots,secondary growth occurs,which makes them look similar in older stages. However,the arrangement of $Protoxylem$ remains a diagnostic feature. In the dicot stem,the $Protoxylem$ is located towards the center (endarch condition),whereas in the dicot root,the $Protoxylem$ is located towards the periphery (exarch condition). This difference persists even after secondary growth,making it the most reliable feature to distinguish between the two.

(C) The ringing or girdling experiment involves removing a ring of bark (phloem) from the stem to demonstrate that phloem is responsible for the translocation of food.
In dicot stems,vascular bundles are arranged in a ring,allowing for the easy removal of the phloem layer without damaging the xylem.
However,in monocots like sugarcane,the vascular bundles are scattered throughout the ground tissue rather than being arranged in a ring.
Therefore,it is impossible to remove a ring of phloem without also damaging the xylem and other tissues,making the experiment ineffective.

(D) The cross-sections of stem and root appear simple when viewed by the naked eye,but under a microscope,they can be differentiated by the $endarch$ condition in the stem and the $exarch$ condition in the root.
In the $endarch$ condition,the $protoxylem$ is present towards the center of the stem,while the $metaxylem$ is towards the periphery.
In the $exarch$ condition,the $protoxylem$ is present towards the periphery (pericycle) and the $metaxylem$ is towards the center of the root.

(A) The first formed primary xylem elements are called protoxylem and the later formed primary xylem is called metaxylem.
In stems,the protoxylem lies towards the centre (pith) and the metaxylem lies towards the periphery of the organ.
This arrangement of primary xylem is known as endarch.

(D) In collateral vascular bundles,the phloem is situated towards the outer side,while the xylem is situated towards the inner side. Therefore,the Assertion is incorrect.
In monocot stems,the vascular bundles are closed,meaning cambium is absent. Therefore,the Reason is also incorrect.
Since both the Assertion and the Reason are false,the correct option is $D$.

(N/A) To distinguish between a monocot and a dicot stem,observe the arrangement and structure of the vascular bundles:
$1$. Dicot Stem:
- Vascular bundles are conjoint,collateral,and open (possess cambium).
- They are arranged in a distinct ring.
- The ground tissue is well-differentiated into hypodermis,cortex,endodermis,pericycle,and a central pith.
$2$. Monocot Stem:
- Vascular bundles are conjoint,collateral,and closed (lack cambium).
- They are scattered throughout the ground tissue.
- Each vascular bundle is surrounded by a sclerenchymatous bundle sheath.
- Phloem parenchyma is absent,and water-containing cavities are often present within the bundles.

(B) The monocot stem is characterized by conjoint,collateral,and closed vascular bundles,which are scattered in the ground tissue.
Each vascular bundle is surrounded by a sclerenchymatous bundle sheath.
Additionally,phloem parenchyma is absent in monocot stems.
Therefore,the given features are diagnostic of a monocot stem.

(N/A) $\rightarrow$ Sunflower is an annual plant with an erect stem.
$\rightarrow$ $A$ transverse section $(TS)$ of a young sunflower stem reveals the following structures:
$(1)$ Epidermis: The outermost protective layer,one cell thick,composed of parenchyma cells. The outer wall is covered with a thin cuticle. It may bear trichomes and a few stomata for gas exchange.
$(2)$ Cortex: Comprises three parts: hypodermis,main cortex,and endodermis.
$(i)$ Hypodermis: Located just below the epidermis,consisting of $3-4$ layers of collenchyma cells. These cells have thickened walls due to cellulose and pectin deposition and lack intercellular spaces. It provides mechanical support.
$(ii)$ Main Cortex: Located below the hypodermis,made of parenchymatous tissue with conspicuous intercellular spaces. The cell walls are thin and cellulosic. Resin ducts may be present in this region. These cells store water and food.
$(iii)$ Endodermis: The innermost layer of the cortex,single-layered,with barrel-shaped parenchymatous cells. These cells contain starch grains,hence it is often called the starch sheath.
$(3)$ Stele: Includes the pericycle,vascular bundles,medullary rays,and pith.
$(i)$ Pericycle: Located inside the endodermis,it is multilayered and composed of sclerenchyma and parenchyma. Sclerenchyma patches located above the vascular bundles are called bundle caps.
$(ii)$ Vascular Bundles: In a sunflower stem,there are $20-25$ vascular bundles arranged in a ring. Each bundle is conjoint,open (possessing cambium),and endarch (protoxylem towards the center).

(N/A) $\rightarrow$ Maize is a monocot plant. When a thin section of its stem is observed under a microscope,the following parts are seen: $(1)$ Epidermis,$(2)$ Ground tissue,$(3)$ Vascular bundles.
$(1)$ Epidermis: It is the outermost layer,consisting of a single layer of parenchymatous cells. The outer walls of these cells are cuticularized.
$\rightarrow$ No stem appendages are produced from this layer,so its surface is soft. Stomata can be seen in this layer. This layer functions in protection and gas exchange.
$(2)$ Ground Tissue: Unlike a dicot stem,distinct regions like cortex,endodermis,and pericycle are not found in the ground tissue.
$\rightarrow$ At the outermost side of the ground tissue,the hypodermis is located. It is made up of two or three layers of sclerenchyma tissue. These cells are non-living and lignified,providing mechanical support to the stem.
$\rightarrow$ Inside the hypodermis,thin-walled parenchyma is located,where vascular bundles are embedded. The ground tissue cells towards the center are comparatively larger and have intercellular spaces.
$(3)$ Vascular Bundles: In a maize stem,numerous vascular bundles are scattered throughout the ground tissue. Peripheral vascular bundles are generally smaller,more numerous,and arranged closer to each other. They are surrounded by a sclerenchymatous bundle sheath.
$\rightarrow$ Centrally located vascular bundles are fewer in number and spaced further apart. Each vascular bundle is surrounded by a sclerenchymatous bundle sheath,making them fibro-vascular bundles.
$\rightarrow$ Each vascular bundle is conjoint,collateral,and closed (lacking cambium).
$\rightarrow$ In the vascular bundles,phloem tissue lies outside and xylem tissue lies inside,arranged in a '$V$' shape.
$\rightarrow$ Phloem tissue: Located outside in a '$V$' shape. Phloem parenchyma is absent.
$\rightarrow$ Xylem tissue: Arranged in the shape of the English alphabet '$V$'. It typically contains three to four vessels. Two large vessels are known as metaxylem,located at the two upper ends of the '$V$',while the protoxylem is located at the base of the '$V$'.

(B) The epidermis is the outermost layer of the maize stem.
It is a single-layered structure composed of parenchyma cells.
The outer walls of these cells are covered by a layer of cuticle.
Trichomes (stem hairs) are generally absent on the epidermis of a maize stem,making its surface smooth.
The primary functions of the epidermis are protection of internal tissues and regulation of gas exchange.

(N/A) Sunflower is an annual plant with a herbaceous stem.
$A$ transverse section of a stained young sunflower stem,when observed under a microscope,reveals the following structures: $(1)$ Epidermis,$(2)$ Cortex,$(3)$ Stele.
$(1)$ Epidermis: It is the outermost protective layer,consisting of a single layer of parenchymatous cells. The outer walls of these cells are covered with a thin layer of cuticle. Multicellular stem hairs (trichomes) arise from these cells. Stomata are present between the cells,which facilitate gaseous exchange.
$(2)$ Cortex: The cortex is divided into three regions: Hypodermis,Main Cortex,and Endodermis.
$(i)$ Hypodermis: The region just below the epidermis is the hypodermis. It consists of $3-4$ layers of collenchyma tissue. The cell walls are thickened with cellulose and pectin. Intercellular spaces are absent. This tissue provides mechanical support.
(ii) Main Cortex: Located below the hypodermis,this region is composed of parenchyma tissue with abundant intercellular spaces. The cell walls are thin and made of cellulose. This region contains resin ducts. The cells store water and food.
(iii) Endodermis: The innermost layer of the cortex is the endodermis,which is single-layered. The cells are barrel-shaped. Since these cells contain starch grains,this layer is also known as the starch sheath.
$(3)$ Stele: The stele includes the pericycle,vascular bundles,and pith.
$(i)$ Pericycle: Located internal to the endodermis,it is multilayered and consists of alternating patches of sclerenchyma and parenchyma. The sclerenchyma patches located above the vascular bundles are called bundle caps.
(ii) Vascular Bundles: In a sunflower stem,$20-25$ vascular bundles are arranged in a ring. Each bundle is conjoint,collateral,and open. The xylem development is endarch. The vascular bundle consists of phloem,cambium,and xylem. The cambium present between the phloem and xylem is called fascicular cambium,which allows for secondary growth.

(A) $(i)$ In roots,root hairs are unicellular extensions of the epidermis. Similarly,in stems,the epidermal outgrowths are called trichomes.
$(ii)$ In dicot stems,the vascular bundles contain cambium between xylem and phloem,making them 'open' vascular bundles. In monocot stems,cambium is absent,making them 'closed' vascular bundles.

(B) $(i)$ Statement $(i)$ is incorrect because fibers are typically thick-walled,lignified,and dead cells,not thin-walled.
$(ii)$ Statement $(ii)$ is correct because in monocot stems (e.g.,maize),the vascular bundles contain water-containing cavities known as lysigenous cavities,which are formed by the dissolution of protoxylem elements.

(B) In $ \text{dicot} $ stems, the vascular bundles are arranged in a ring.
In contrast, in $ \text{monocot} $ stems, the vascular bundles are scattered throughout the ground tissue.

(B) $\Rightarrow$ The epidermis is the outermost layer of the maize stem.
$\Rightarrow$ It consists of a single layer of parenchymatous cells.
$\Rightarrow$ The outer walls of these cells are cuticularized to prevent water loss.
$\Rightarrow$ No stem appendages (like trichomes) are produced from this layer,making the surface smooth.
$\Rightarrow$ Stomata are present in this layer,which facilitate gas exchange and transpiration.
$\Rightarrow$ The primary functions of the epidermis are protection of internal tissues and regulation of gas exchange.

$(B)$ The anatomical features described are characteristic of a $Monocotyledonous$ stem:
$1$. Scattered vascular bundles: In monocot stems, vascular bundles are scattered throughout the ground tissue.
$2$. Bundle sheath: Each vascular bundle is surrounded by a sclerenchymatous bundle sheath.
$3$. Ground tissue: The ground tissue is large, conspicuous, and parenchymatous.
$4$. Conjoint and closed vascular bundles: The bundles are conjoint (xylem and phloem together) and closed (no cambium present, so secondary growth does not occur).
$5$. Phloem parenchyma: Phloem parenchyma is typically absent in monocot stems.
Therefore, the correct option is $B$.

(A) The characteristics described are typical of a monocot stem:
$1$. Scattered vascular bundles are a hallmark of monocot stems.
$2$. The presence of a bundle sheath around vascular bundles is common in monocots.
$3$. Vascular bundles are conjoint (xylem and phloem together) and closed (no cambium present,hence no secondary growth).
$4$. Phloem parenchyma is absent in monocot stems.
$5$. The ground tissue is undifferentiated and parenchymatous.
Therefore,the correct option is $A$.

(A) In monocot stems,the vascular bundles are described as conjoint,collateral,and closed.
Conjoint means xylem and phloem are present in the same bundle.
Collateral means phloem is located on the outer side and xylem on the inner side.
Closed means cambium is absent between xylem and phloem,which prevents secondary growth.

(D) The ring arrangement of vascular bundles is a characteristic feature of the dicot stem.
In dicot stems,the vascular bundles are arranged in a ring around the pith.
Each vascular bundle is conjoint,collateral,open (possessing cambium),and exhibits endarch protoxylem.

(C) In a dicotyledonous stem,the anatomical arrangement of tissues from the periphery (outside) towards the center (inside) is as follows:
$1$. Phellem (Cork): The outermost protective layer formed by the cork cambium.
$2$. Endodermis: The layer located inner to the cortex.
$3$. Pericycle: The layer situated between the endodermis and the vascular bundles.
$4$. Phloem: The vascular tissue responsible for food transport,located inner to the pericycle.
$5$. Xylem: The innermost vascular tissue.
Therefore,the correct sequence is Phellem $\rightarrow$ endodermis $\rightarrow$ pericycle $\rightarrow$ phloem $\rightarrow$ xylem.

(B) The transverse section of a typical young dicotyledonous stem shows that the epidermis is the outermost protective layer of the stem,covered with a thin layer of cuticle. It may bear trichomes and a few stomata.

(D) The cortex in a dicot stem is located between the epidermis and the stele. It consists of three sub-zones:
$1$. Hypodermis: Located just below the epidermis,composed of collenchyma cells.
$2$. Cortical layers: Located below the hypodermis,composed of thin-walled parenchyma cells.
$3$. Endodermis: The innermost layer of the cortex.
Therefore,the cortex consists of $I$ (hypodermis),$II$ (cortical layers),and $IV$ (endodermis). The epidermis $(V)$ is the outermost layer of the stem,and the pericycle $(III)$ is part of the stele,not the cortex. Thus,the correct answer is all except $III$ and $V$.

(D) In a monocot stem,the ground tissue is not differentiated into distinct regions like cortex,endodermis,pericycle,and pith. Instead,it consists of a mass of parenchyma cells. Therefore,the endodermis and cortex are absent as distinct layers in the monocot stem. The hypodermis is present (usually sclerenchymatous). Thus,endodermis and cortex are the structures that are absent.

(D) The given diagram represents the transverse section $(T.S.)$ of a Dicot stem.
$A$ represents Collenchyma,which is present just below the epidermis.
$B$ represents Parenchyma,which forms the cortex.
$C$ represents the Cambium,which is located between the xylem and phloem.
$D$ represents Protoxylem,which is the first-formed xylem.
$E$ represents the Pith,which is the central part of the stem.
Therefore,the correct sequence is $A-$ Collenchyma,$B-$ Parenchyma,$C-$ Cambium,$D-$ Protoxylem,$E-$ Pith.

(B) In plant anatomy,the pith (medulla) consists of parenchymatous cells located in the center of the stem or root.
$1$. In $Dicot$ stems,a large,well-developed,and prominent pith is present in the center.
$2$. In $Monocot$ roots,a large and well-developed pith is also present.
$3$. In $Dicot$ roots,the pith is generally small or absent,and the center is occupied by the xylem.
$4$. In $Monocot$ stems,the vascular bundles are scattered throughout the ground tissue,and there is no distinct pith.
Therefore,a clear and prominent pith is characteristic of the $Dicot$ stem and $Monocot$ root.

(D) Vessels are specialized water-conducting cells found in most angiosperms. However,they are absent in some primitive angiosperms,such as $Drimys$. These plants are referred to as homoxylous angiosperms because their xylem consists only of tracheids.

(B) In the endarch condition of primary xylem,the protoxylem lies towards the center (pith) and the metaxylem lies towards the periphery of the organ. This arrangement is a characteristic feature of stems in both dicot and monocot plants.

(D) In monocot stems,the vascular bundles are scattered in the ground tissue. Each vascular bundle is surrounded by a layer of sclerenchymatous cells known as the bundle sheath. This is a characteristic anatomical feature of monocot stems.

(A) In monocot stems,the vascular bundles are scattered in the ground tissue. Each vascular bundle is surrounded by a layer of sclerenchymatous cells known as the bundle sheath. Therefore,the correct answer is the sclerenchymatous bundle sheath.

(C) In monocotyledonous stems,the vascular bundles are scattered throughout the ground tissue. Each vascular bundle is conjoint,collateral,and closed (lacking cambium). Additionally,they contain water-containing cavities known as lysigenous cavities or protoxylem lacunae. The 'ring' arrangement of vascular bundles is a characteristic feature of dicotyledonous stems,not monocotyledonous stems. Therefore,the statement that they have a 'ring' arrangement is incorrect.

(B) In dicot stems,the vascular bundles are described as conjoint,collateral,and open.
Conjoint means xylem and phloem are present on the same radius.
Collateral means phloem is located towards the outer side (pericycle) and xylem is located towards the inner side (pith).
Open means a strip of cambium is present between the xylem and phloem,which allows for secondary growth.
Therefore,option $B$ is correct.

(D) In a typical monocot stem,the vascular bundles are scattered,conjoint,collateral,and closed (lacking cambium). The hypodermis is sclerenchymatous. However,the presence of a 'water canal' (lysigenous cavity) is a characteristic feature found within the vascular bundles themselves,not in the pith. Furthermore,monocot stems typically lack a distinct bundle sheath surrounding the vascular bundles,which is a characteristic feature of monocot leaves. Therefore,the statement 'Presence of bundle sheath' is not true for a monocot stem.