Internal structure of stem Questions in English

(D) Vascular bundles that lack cambium between xylem and phloem are known as closed vascular bundles,which are characteristic of monocot stems. Maize,Barley,and Wheat are monocots and possess closed vascular bundles. Sunflower is a dicot plant,and its stems possess open vascular bundles,meaning cambium is present between the xylem and phloem,allowing for secondary growth.

$(C)$ In a $Dicot$ stem, the epidermis typically possesses trichomes (multicellular hairs).
In a $Monocot$ stem, the vascular bundles are scattered and often contain water-containing cavities (lysigenous cavities) within the xylem.
Therefore, option $C$ represents the correct match for the anatomical features of $Dicot$ and $Monocot$ stems respectively.

(D) In monocot stems,the vascular bundles are scattered throughout the ground tissue,whereas in dicot stems,they are arranged in a ring. Additionally,monocot stems lack a distinct pith and cortex,unlike dicot stems which have a well-developed pith.

(D) Maize ($Zea$ $mays$) is a monocotyledonous plant. In monocot stems,the endodermis is usually absent or not well-defined. Therefore,the Assertion is incorrect.
Monocot stems possess an atactostele (scattered vascular bundles),whereas a eustele (vascular bundles arranged in a ring) is a characteristic feature of dicot stems. Therefore,the Reason is also incorrect.
Thus,both Assertion and Reason are incorrect.

(B) Plants that live in an abundance of water are called hydrophytes.
Hydrophytic plants that remain completely under water are called submerged hydrophytes.
These plants possess extensively developed air spaces (aerenchyma) in their roots,stems,and leaves to facilitate buoyancy and gas exchange.
$e.g.,$ $Hydrilla$,$Vallisneria$,$Ceratophyllum$,$Utricularia$,etc.

(B) In plants,the arrangement of xylem is classified based on the position of protoxylem and metaxylem.
$1$. $Endarch$: The protoxylem lies towards the center (pith) and the metaxylem lies towards the periphery. This is characteristic of stems.
$2$. $Exarch$: The protoxylem lies towards the periphery and the metaxylem lies towards the center. This is characteristic of roots.
$3$. $Mesarch$: The protoxylem is surrounded by metaxylem on all sides.
Since the question states that the protoxylem is towards the center,the correct arrangement is $Endarch$.

(A) Open vascular bundles are those that contain cambium between the xylem and phloem,allowing for secondary growth.
$1$. Dicot root: Vascular bundles are radial and closed.
$2$. Dicot stem: Vascular bundles are conjoint,collateral,and open (contain cambium).
$3$. Monocot root: Vascular bundles are radial and closed.
$4$. Monocot stem: Vascular bundles are conjoint,collateral,and closed (no cambium).
$5$. Dicot leaf: Vascular bundles are closed.
$6$. Monocot leaf: Vascular bundles are closed.
Only the Dicot stem possesses open vascular bundles. Therefore,the count is $1$.

(A) $1$. Radial vascular bundles: In these bundles,xylem and phloem are arranged in an alternate manner on different radii. This arrangement is characteristic of roots (both monocot and dicot).
$2$. Conjoint vascular bundles: In these bundles,xylem and phloem are jointly situated at the same radius. This arrangement is characteristic of stems and leaves.
$3$. Therefore,radial vascular bundles are found in roots (e.g.,Monocot root),and conjoint vascular bundles are found in stems (e.g.,Monocot stem).
$4$. Thus,the correct option is $A$.

(D) The epidermis is the outermost layer of the stem.
It is covered by a thin,waxy layer called the $Cuticle$ to prevent water loss.
It also contains $Trichomes$ (epidermal hairs) which are multicellular outgrowths.
$Stomata$ are also present in the epidermis of the stem to facilitate gaseous exchange.
Therefore,all these structures are characteristic features of the stem epidermis.

$(C)$ In a dicot stem, the pericycle is present above the phloem in the form of semi-lunar patches of sclerenchyma. Therefore, it is sclerenchymatous.
In a dicot root, the pericycle is the layer next to the endodermis and is composed of thin-walled parenchymatous cells. It is responsible for the initiation of lateral roots and part of the vascular cambium during secondary growth.
Thus, the correct match is that the dicot stem pericycle is sclerenchymatous and the dicot root pericycle is parenchymatous, which corresponds to option $C$.

(A) The provided diagram represents the transverse section of a dicot stem.
In a dicot stem:
$P$ points to the Hypodermis,which is the layer just below the epidermis.
$Q$ points to the Pericycle,which is present above the phloem.
$R$ points to the Medullary ray,which is the radial strip of parenchyma cells between the vascular bundles.
Therefore,the correct identification is $P=$ Hypodermis,$Q=$ Pericycle,$R=$ Medullary ray.

(B) The provided image shows a closed,collateral vascular bundle with a $Y$-shaped arrangement of xylem vessels,which is characteristic of a monocot stem. In monocot stems,vascular bundles are scattered and closed (lacking cambium). Monocot leaves also have closed vascular bundles,but the specific 'monkey face' appearance of the xylem vessels (two large metaxylem vessels and smaller protoxylem vessels) is a classic diagnostic feature of a monocot stem cross-section.

(C) The provided figure shows a transverse section of a monocot stem. In a monocot stem,the vascular bundles are scattered throughout the ground tissue. The label '$P$' points to these scattered vascular bundles. Therefore,the correct option is 'Vascular bundle'.

(D) Vascular bundles are described as 'conjoint' when xylem and phloem are present on the same radius. They are 'collateral' when phloem lies towards the outer side and xylem towards the inner side. They are 'open' when a strip of cambium is present between xylem and phloem,which allows for secondary growth. These features are characteristic of the dicot stem.

(B) In a $Monocot$ stem,the vascular bundles are scattered in the ground tissue. The ground tissue is not differentiated into distinct regions like cortex,endodermis,pericycle,and pith. In contrast,these regions are well-defined in dicot stems and roots.

(A) In a monocot stem,the hypodermis is typically sclerenchymatous,not parenchymatous. This layer provides mechanical support to the stem.
- Vascular bundles are scattered throughout the ground tissue.
- Vascular bundles are conjoint (xylem and phloem together) and closed (no cambium present).
- Phloem parenchyma is generally absent in the vascular bundles of monocot stems.
Therefore,the statement 'Hypodermis is parenchymatous' is incorrect.

(D) In the vascular bundles of monocot stems like $Maize$ ($Zea$ $mays$),the protoxylem elements disintegrate to form a lysigenous cavity known as the water cavity or protoxylem lacuna. This cavity helps in the conduction of water. Therefore,the water cavity is characteristic of the monocot stem.

(D) In dicot stems,the innermost layer of the cortex is known as the endodermis.
This layer is rich in starch grains and is therefore commonly referred to as the $Starch \ sheath$.
It serves as a storage site for starch and helps in the regulation of water and solute movement.
Therefore,the correct option is $D$.

(C) In plants,the anatomical structure varies between roots and stems.
$1$. In roots (both dicot and monocot),the endodermis and pericycle are present as distinct layers. The endodermis is the innermost layer of the cortex,and the pericycle is located just inside the endodermis.
$2$. In stems,the organization is different. In a dicot stem,the endodermis is often referred to as the starch sheath,but it is not always clearly defined as a continuous layer.
$3$. However,in a monocot stem,the vascular bundles are scattered throughout the ground tissue,and there is no distinct endodermis or pericycle layer surrounding the vascular tissue.
Therefore,pericycle and endodermis are not found in the monocot stem.

(A) The provided figure represents the transverse section of a monocot stem.
$1$. $A$ points to the vascular bundles,which are scattered throughout the ground tissue.
$2$. $B$ points to the outermost layer,the epidermis.
$3$. $C$ points to the hypodermis,which is located just below the epidermis.
$4$. $D$ points to the ground tissue,which fills the space between the vascular bundles.
Therefore,the correct identification is $A -$ Vascular bundle,$B -$ Epidermis,$C -$ Hypodermis,$D -$ Ground tissue.

(B) $1$. In $Monocot$ stems,vascular bundles are conjoint,collateral,and closed (lacking cambium).
$2$. In $Dicot$ stems,vascular bundles are conjoint,collateral,and open (possessing cambium).
$3$. In roots,vascular bundles are always radial,meaning xylem and phloem are arranged in alternate radii,and they are closed (lacking cambium).
$4$. Therefore,statement $B$ is correct because $Dicot$ stems contain open vascular bundles,which allow for secondary growth.

(B) The hypodermis is the layer of cells located just below the epidermis.
In dicot stems,the hypodermis is typically composed of collenchyma cells,which provide mechanical support and flexibility to the young stem.
In contrast,monocot stems usually have a sclerenchymatous hypodermis,and roots generally lack a distinct hypodermis.
Therefore,the correct answer is $B$ (Dicot stem).

(C) In a $dicot$ stem,the vascular bundles are arranged in a ring around the pith.
This arrangement is a diagnostic feature of $dicot$ stems.
In contrast,$monocot$ stems have scattered vascular bundles throughout the ground tissue.
$Dicot$ leaves have a dorsiventral structure with vascular bundles in the veins,and $monocot$ roots have a radial arrangement of vascular bundles.

(A) The anatomical features described are characteristic of a $Dicotyledonous$ stem.
$(1)$ $Collenchymatous$ hypodermis is a typical feature of $Dicot$ stems, providing mechanical strength.
$(2)$ $Sclerenchymatous$ pericycle in the form of semi-lunar patches above the phloem is a diagnostic feature of $Dicot$ stems.
$(3)$ Vascular bundles arranged in a ring is a hallmark of $Dicot$ stems.
$(4)$ $Conjoint$ and $open$ vascular bundles (possessing cambium) allow for secondary growth, which is characteristic of $Dicot$ stems.
Therefore, the correct answer is $Dicotyledonous$ stem.

(B) In a dicot stem,the hypodermis is located just below the epidermis.
It consists of collenchyma cells.
Collenchyma is a living mechanical tissue that provides tensile strength and flexibility to the young,growing stem.
Therefore,the hypodermis is responsible for providing mechanical strength to the young stem.

(C) In the internal structure of a $Dicotyledonous$ stem, the innermost layer of the cortex is called the endodermis. Because the cells of the endodermis are rich in starch grains, it is also referred to as the $Starch$ $sheath$.
Additionally, the patches of $Sclerenchyma$ cells present above the phloem bundles are known as $Bundle$ $cap$.

(A) The characteristics described—innumerable scattered vascular bundles,absence of cambium (closed bundles),and lack of a well-demarcated pith—are diagnostic features of a monocot stem.
Among the given options,the $Maize$ stem is a monocot stem.
In contrast,the $Sunflower$ stem is a dicot stem,which possesses a ring-like arrangement of vascular bundles,presence of cambium,and a distinct pith.
Roots (both monocot and dicot) typically have a radial arrangement of vascular bundles,not scattered ones.

(D) The vascular bundles are described as conjoint,collateral,and open.
$1$. Conjoint: Xylem and phloem are present on the same radius.
$2$. Collateral: Phloem is located towards the outer side and xylem towards the inner side.
$3$. Open: The presence of cambium between xylem and phloem allows for secondary growth.
These characteristics are diagnostic features of a Dicot Stem.
In contrast,Monocot stems have closed vascular bundles (no cambium),and roots have radial vascular bundles (xylem and phloem on different radii).