Meristematic Tissue Questions in English

(A) Viruses usually infect the whole plant except the stem apex (shoot apical meristem).
This is because the apical meristematic cells have a high concentration of growth hormones,such as auxins,which inhibit viral replication and movement.
Additionally,the rapid rate of cell division in the apical meristem often outpaces the spread of the virus,keeping these regions virus-free.

(C) The needles of $Pinus$ (a gymnosperm) possess meristematic tissue at their base. This basal meristem allows for the continuous growth of the needle throughout its lifespan. Therefore,the correct option is $C$.

(A) The Tunica-corpus theory was proposed by Schmidt in $1924$.
This theory explains the organization of the shoot apical meristem in angiosperms.
It recognizes two distinct zones: the tunica (peripheral layer) and the corpus (central mass of cells).

(C) The Histogen theory was proposed by Hanstein in $1870$.
According to this theory,the shoot apex is composed of $3$ distinct layers of initials,which are:
$1$. Dermatogen: The outermost layer that gives rise to the epidermis.
$2$. Periblem: The middle layer that gives rise to the cortex.
$3$. Plerome: The central core that gives rise to the stele (vascular tissues).

(A) The term "protoderm" was coined by $Haberlandt$ in $1914$.
$Haberlandt$ introduced new terminology for the meristematic zones derived from the apical meristem to replace the older terms proposed by $Hanstein$.
Specifically, he proposed "protoderm" instead of "dermatogen", "ground meristem" instead of "periblem", and "procambium" instead of "plerome".

(B) According to the histogen theory proposed by Hanstein $(1870)$,the shoot apex is differentiated into three distinct meristematic zones or layers:
$(a)$ Dermatogen: It is the outermost layer that forms the epidermis.
$(b)$ Periblem: It is the middle layer that gives rise to the cortex and endodermis.
$(c)$ Plerome: It is the central core that forms the pericycle,vascular bundles,medullary rays,and pith.
Since these layers are responsible for the formation of various plant tissues through continuous cell division,they are classified as meristematic tissues.

(A) According to the Histogen theory proposed by Hanstein,the apical meristem of the root is divided into three distinct zones or histogens:
$1$. Dermatogen: The outermost layer which gives rise to the epidermis (or epiblema in roots).
$2$. Periblem: The middle layer which gives rise to the cortex.
$3$. Plerome: The central core which gives rise to the stele (vascular tissues like xylem and phloem,and pith).
Therefore,the correct answer is the epidermis.

(C) . Intercalary meristem is responsible for the elongation of the stem in grasses. It is a type of primary meristem that occurs between mature tissues and is found in the internodal regions of monocots like grasses,allowing them to regenerate parts removed by grazing herbivores.

(D) The Tunica-Corpus theory was proposed by Schmidt in $1924$.
This theory explains the organization of the shoot apical meristem in angiosperms.
According to this theory,the shoot apex consists of two distinct zones:
$(1)$ Tunica: The peripheral layer$(s)$ of cells that divide anticlinally to increase the surface area.
$(2)$ Corpus: The central mass of cells that divide in various planes to increase the volume of the shoot apex.
Therefore,it is related to the shoot apex.

(A) Lateral meristems occur laterally in the axis,parallel to the sides of stems and roots.
They are responsible for secondary growth,which increases the girth of the plant.
The vascular cambium (including fascicular,interfascicular,and extrastelar cambium) and the cork cambium (phellogen) are primary examples of lateral meristems.

(A) The apical meristem is responsible for primary growth in plants.
These cells are located at the tips of roots and shoots.
They divide actively in different planes,leading to an increase in the length of the plant axis.

(D) Actively growing plant tissues,such as meristematic tissues,require a high amount of water to maintain turgor pressure for cell expansion and to facilitate metabolic processes. These tissues typically have a high water content,generally ranging between $85\%$ and $95\%$. Therefore,option $D$ is the correct answer.

(D) The root apical meristem is covered by a protective structure called the root cap. In many plants,particularly monocots,this root cap is formed by a specific layer of cells known as the $Calyptrogen$. According to the histogen theory proposed by Hanstein,the root apex consists of three histogens: $Dermatogen$ (forms epidermis),$Periblem$ (forms cortex),and $Plerome$ (forms stele). The $Calyptrogen$ is considered the fourth histogen responsible for the formation of the root cap.

(C) The root cap in dicotyledonous plants is derived from a specialized meristematic region known as the $Calyptrogen$.
$Calyptrogen$ is a specific layer of cells located at the root apex that undergoes rapid division to produce the root cap,which protects the delicate root apical meristem as it pushes through the soil.
$Protoderm$ gives rise to the epidermis,$Ground \ meristem$ forms the cortex and pith,and $Procambium$ develops into the vascular tissue system.

(B) Meristematic cells are characterized by their ability to divide actively.
These cells possess thin primary cell walls made of cellulose.
They are typically isodiametric (equal in diameter) and contain a prominent,large nucleus.
Crucially,they are filled with dense,granular protoplasm to support high metabolic activity and rapid cell division.
Therefore,the correct description is thin-walled,isodiametric,nucleate,and densely protoplasmic.

(D) Promeristem is the earliest stage of meristematic tissue found at the extreme tips of shoots and roots. It is characterized by its high power of active division,its specific apical position,and the presence of a large,prominent nucleus in its cells. Since all these features are characteristic of promeristems,the correct answer is $D$.

(B) Meristematic tissue consists of actively dividing cells that are responsible for the growth of the plant.
These tissues are located in specific regions known as meristems.
Apical meristems are found at the tips of roots and shoots (stem apex),where they facilitate primary growth.
Buds also contain meristematic tissue that gives rise to new branches or flowers.
However,between the given options,the stem apex is a primary site of active meristematic division for vertical growth.
Therefore,the correct answer is $B$.

(A) . Lateral meristem is responsible for increasing the girth of the plant.
These meristems occur laterally in the axis,parallel to the sides of stems and roots.
This meristem consists of initials which divide mainly in one plane $(periclinal)$ and result in an increase in the diameter of an organ.

(B) On the basis of origin,meristematic tissues are classified into $3$ groups:
$1$. Promeristem (Primordial meristem)
$2$. Primary meristem
$3$. Secondary meristem
Therefore,the correct option is $B$.

(A) Intercalary meristems are a type of primary meristem found in grasses and other monocots.
They are located between mature tissues and are responsible for the elongation of internodes.
Since they contribute to the increase in the length of the plant body,they are responsible for primary growth.
Secondary growth is associated with lateral meristems like vascular cambium and cork cambium.

(A) The primary meristems in the shoot and root apices differentiate into three distinct types of tissues:
$1$. The outermost layer is the protoderm,which gives rise to the epidermis.
$2$. The procambium gives rise to the primary vascular tissues (xylem and phloem).
$3$. The ground meristem gives rise to the ground tissue system (cortex,endodermis,pericycle,and pith).
Therefore,the outermost primary meristem (protoderm) gives rise to the epidermis.

(A) The root epidermis is known as epiblema or piliferous layer. During primary growth in plants,the apical meristem differentiates into three primary meristems: protoderm,procambium,and ground meristem. The protoderm is the outermost layer of the apical meristem,which gives rise to the epidermis in stems and the epiblema in roots.

(B) . The secondary meristems,such as the cork cambium $(phellogen)$,are responsible for the formation of secondary tissues. These tissues are essential for the repair of injured plant parts and provide effective protection to the plant body through the formation of periderm.

(D) The Histogen theory,proposed by $Hanstein$,suggests that the root and shoot apices consist of three distinct meristematic zones or histogens: $Dermatogen$,$Periblem$,and $Plerome$.
$Dermatogen$ is the outermost layer of the apical meristem.
It is responsible for the formation of the epidermis and the epidermal tissue system in plants.
Therefore,the correct option is $D$.

(C) The $Apical \text{ meristem}$ is located at the growing tips of stems and roots.
During the formation of leaves and the elongation of the stem, some cells are left behind from the shoot apical meristem.
These cells constitute the $Axillary \text{ bud}$, which is present in the axils of leaves and is capable of forming a branch or a flower.
The $Terminal \text{ bud}$ (or shoot apex) is the primary meristematic region responsible for the longitudinal growth of the plant.
Therefore, both axillary and terminal buds are derived from the activity of the $Apical \text{ meristem}$.

(B) The classification of meristems based on the plane of cell division is as follows:
$1$. $Plate$ $meristem$: Divisions occur in two planes,resulting in the formation of plate-like structures (e.g.,leaf lamina).
$2$. $Ground$ $meristem$: Divisions occur in all planes,leading to the formation of a massive,three-dimensional body (e.g.,cortex,pith).
$3$. $File$ $meristem$: Divisions occur in only one plane,resulting in the formation of rows or files of cells.
$4$. $Lateral$ $meristem$: These are responsible for secondary growth and typically divide in a tangential plane.
Therefore,the $Ground$ $meristem$ is the one where cell divisions occur in all planes.

(A) Totipotency is the ability of a single cell to divide and produce all the differentiated cells in an organism.
Meristematic cells are undifferentiated,actively dividing cells that retain the capacity to develop into any type of plant tissue.
Sieve tubes,collenchyma,and xylem vessels are differentiated cells that have lost their ability to divide and are specialized for specific functions like transport or structural support.

(B) The root apical meristem is located behind the root tip. Because the root tip is covered by a protective structure called the root cap,the meristematic region is positioned slightly behind the apex,making it sub-terminal or sub-apical.

(A) Meristems are regions of actively dividing cells in plants.
In $Cycas$,the stem contains apical meristems that are responsible for the growth of the plant body.
Fern leaves and pollen grains are mature structures that generally lack active meristematic tissue.
Fern rhizomes do contain meristematic regions at the tips,but $Cycas$ stem is a classic example of primary growth regions in gymnosperms.

(A) The promeristem represents the earliest stage of meristematic tissue development.
It originates from the embryo and is therefore referred to as the primordial or embryonic meristem.
It is the region of the plant body that is capable of continuous division and gives rise to primary meristems like the root and shoot apices.

(C) Meristematic tissues are regions of active cell division in plants.
$1$. Apical meristems are found at the tips of stems and roots,responsible for primary growth.
$2$. Lateral meristems,such as vascular cambium and cork cambium,are responsible for secondary growth (increase in girth).
Therefore,stem and root apices,vascular cambium,and cork cambium are all examples of meristematic tissues.

(B) Primary vascular tissues,which include primary xylem and primary phloem,are derived from the procambium.
$1$. The procambium is a primary meristematic tissue that differentiates into the vascular tissues of the plant.
$2$. Protoderm gives rise to the epidermis.
$3$. Ground meristem gives rise to the ground tissue system (cortex,pith,etc.).
$4$. Calyptrogen is responsible for the formation of the root cap.

(A) The shoot apical meristem gives rise to three primary meristems: the protoderm, the procambium, and the ground meristem.
$1$. The $Protoderm$ is the outermost layer of the apical meristem and is responsible for the formation of the epidermis.
$2$. The $Procambium$ gives rise to the primary vascular tissues (xylem and phloem).
$3$. The $Ground$ meristem develops into the ground tissue system, which includes the cortex, endodermis, pericycle, and pith.
Therefore, the epidermis is derived from the $Protoderm$.

(D) Secondary meristems are those meristems that develop from mature,differentiated permanent tissues through the process of dedifferentiation.
Examples include the cork cambium (phellogen) and the interfascicular cambium,which arise from parenchyma cells of the cortex and medullary rays,respectively,after the cells have already attained maturity.

(A) Intercalary meristems are meristematic tissues that are present between permanent tissues. They are primarily found at the base of the node (nodal region),such as in $Mentha$ $viridis$ (Mint),at the base of the internode,such as in the stems of wheat and grasses,and at the base of the leaf,such as in $Pinus$. These meristems are responsible for the elongation of the internodes and the growth of leaves.

(A) Intercalary meristem is a type of primary meristem that occurs between mature tissues. It is typically found in the internodes of monocotyledonous plants,such as grasses (e.g.,paddy,wheat,bamboo),to allow for the elongation of the stem. Among the given options,paddy is a monocot plant,which possesses intercalary meristems at the base of the internodes.

(A) Primary growth in plants refers to the increase in length of the plant body.
This growth is primarily driven by the activity of apical meristems,which include the shoot apical meristem and the root apical meristem.
These meristems continuously divide to produce new cells that differentiate into primary tissues,leading to the elongation of stems and roots.
Vascular cambium is responsible for secondary growth (increase in girth),not primary growth.
Root caps protect the root meristem but do not contribute to growth themselves.
Primary growth continues throughout the life of the plant at the tips of roots and shoots.

(B) The quiescent centre is a small group of cells located at the root apex where the rate of cell division is very low or absent.
These cells act as a reservoir of stem cells that can resume division if the primary meristematic cells are damaged.
Therefore,the quiescent centre is found in the root tip.

(D) The term 'meristem' was coined by the Swiss botanist $C. Nageli$ in $1858$. He used this term to describe the tissues in plants that are composed of actively dividing cells,which are responsible for the growth of the plant body.

(D) Meristematic tissues consist of actively dividing cells. Key characteristics include:
$1$. Thin primary cell walls composed of cellulose.
$2$. Absence of intercellular spaces due to their compact arrangement.
$3$. Dense cytoplasm with very small or no vacuoles.
$4$. Large,prominent nuclei indicating high metabolic activity.
Since all the statements provided in options $A$,$B$,and $C$ are standard characteristics of meristematic cells,option $D$ is the correct choice.

(D) $Cambium$ is a type of lateral meristematic tissue found in dicot plants.
Meristematic tissues are composed of actively dividing cells that contribute to the growth of the plant.
$Epidermis$,$Cortex$,and $Hypodermis$ are examples of permanent tissues,which are composed of cells that have lost the ability to divide.

(C) Meristematic cells are actively dividing cells that require flexibility and rapid growth.
They possess a thin,flexible primary cell wall and a middle lamella that connects adjacent cells.
Secondary cell walls are typically deposited only after the cell has ceased division and undergone differentiation (maturation) to provide structural support.
Therefore,the secondary wall is absent in meristematic cells.

(C) Active cell division in plants occurs in regions known as meristems.
Meristematic tissues are responsible for the growth of the plant.
The tip of the stem contains the shoot apical meristem,which is a primary site of active cell division and growth.
Cortex,pith,and internodal regions consist mostly of permanent tissues that have already undergone differentiation and are generally not sites of active cell division.

(A) The embryo of a seed is composed of cells that are actively and rapidly dividing to facilitate the growth and development of the new plant. These undifferentiated,actively dividing cells are known as meristematic tissue. Therefore,the correct answer is $A$.

(C) Intercalary meristems are meristematic tissues that are present between permanent tissues.
They are found in the internodes of grasses and at the base of leaves (petioles) or internodes.
They are responsible for the elongation of the internodes and the growth of leaves.
Therefore,the correct location for intercalary meristem is the petiole and internode.

(D) Meristematic tissue is a group of cells that possess the ability to divide continuously.
These cells are undifferentiated and are responsible for the growth of the plant body.
As these cells divide,they produce new cells that eventually differentiate into permanent tissues.
Therefore,the defining characteristic of meristem is the continuous division of cells to give rise to new ones.

(A) The apical meristem is located at the growing apices of main and lateral shoots and roots. These cells are responsible for the linear growth (increase in length) of a plant organ.

(A) According to the Histogen theory proposed by Hanstein,the root and shoot apices are differentiated into three distinct meristematic zones called histogens: dermatogen,periblem,and plerome. These histogens are components of the apical meristem,which is responsible for the primary growth of the plant body.