Secondary growth Questions in English

(C) In $Cycas$,the secondary growth is anomalous. It is brought about by the formation of successive rings of cambium. As the first cambium ring ceases to function,a new cambium ring is formed from the cortical cells outside the previous one. This process repeats,leading to the formation of multiple rings of vascular tissues (up to $22$ rings have been observed in older stems).

(D) Secondary growth is the increase in thickness or girth of the plant body, which occurs due to the activity of the vascular cambium and cork cambium.
$Riccia$ and $Funaria$ are bryophytes, which lack vascular tissues and therefore do not exhibit secondary growth.
$Selaginella$ is a pteridophyte that shows a limited form of secondary growth in its stem, but it is not considered typical secondary growth as seen in seed plants.
Typical secondary growth is a characteristic feature of dicotyledonous angiosperms and gymnosperms.
Since none of the options represent typical secondary growth as found in higher plants, the correct answer is $None \, of \, these$.

(B) Technically, wood is $Secondary$ $xylem$ formed by vascular cambium during secondary growth. As the plant matures, the vascular cambium produces secondary xylem towards the inner side, which accumulates over time and is commonly referred to as wood.

(B) The correct answer is $B$.
$Tyloses$ are balloon-like outgrowths of xylem parenchyma cells that protrude into the lumen of a vessel or tracheid through the pits.
They are commonly formed in older wood and help in blocking the water-conducting pathway,often leading to the formation of heartwood.

(A) The fascicular cambium (within vascular bundles),interfascicular cambium (between vascular bundles),and extra-stelar cambium (cork cambium or phellogen) are all responsible for secondary growth in plants.
These tissues divide periclinally to increase the girth or diameter of the plant axis.
Since they are located parallel to the longitudinal axis of the plant and contribute to secondary growth,they are classified as lateral meristems.

(D) Tyloses are bladder-like outgrowths of parenchyma cells that protrude into the lumen of xylem vessels through the pits.
They are typically formed during secondary growth in older wood and serve to block the continuity of the conducting system.
These structures are commonly found in both xylem vessels and associated ray parenchyma cells.

(B) Trees are woody plants that possess secondary growth,which involves the deposition of secondary cell walls.
These secondary cell walls are primarily composed of cellulose,hemicellulose,and lignin.
The combination of these components,particularly cellulose and lignin,is collectively referred to as lignocellulose.
Lignin provides structural rigidity and strength to the tree,while cellulose provides tensile strength.
Therefore,trees contain a large amount of lignocellulose.

(B) The correct answer is $B$. Lignification is the process of depositing lignin in the cell walls of plants. Lignin is a complex organic polymer that provides structural support,rigidity,and water-proofing to the xylem vessels and tracheids,which makes the plant tissues woody and strong.

(C) The vascular cambium in roots is formed during secondary growth.
It originates from the dedifferentiation of parenchyma cells (such as conjunctive tissue and pericycle cells) located between the primary xylem and primary phloem.
Since it develops from permanent tissues that have regained the ability to divide,it is classified as a secondary meristem.

(D) The terms $Exarch$,$Endarch$,and $Mesarch$ describe the arrangement of $Protoxylem$ and $Metaxylem$ in primary xylem based on the position of the $Protoxylem$ relative to the center of the organ.
Secondary xylem is formed by the activity of the vascular cambium and consists of tracheids,vessels,xylem fibers,and xylem parenchyma.
Since secondary xylem does not exhibit the differentiation into $Protoxylem$ and $Metaxylem$ seen in primary tissues,these terms are not applicable to secondary xylem.
Therefore,the correct option is $D$.

(C) Secondary meristems are those that develop from permanent tissues during the process of secondary growth in plants.
$1$. Protoderm and Procambium are examples of primary meristems,as they are derived from the promeristem and are responsible for the primary growth of the plant.
$2$. Cork cambium (phellogen) and vascular cambium (in dicot stems) are examples of secondary meristems.
$3$. Therefore,among the given options,Cork cambium is a secondary meristem.

(C) In a woody dicotyledonous tree,secondary growth occurs in the stem and root,leading to the formation of secondary tissues (secondary xylem and phloem).
However,parts like flowers,fruits,and leaves do not undergo secondary growth and are composed primarily of primary tissues throughout their lifespan.
Therefore,these organs remain in the primary state of development.

(B) Cork tissue,also known as phellem,arises from the cork cambium,which is scientifically called $phellogen$.
$Phellogen$ is a secondary meristematic tissue that undergoes periclinal divisions to produce cork cells on the outer side and secondary cortex $(phelloderm)$ on the inner side.
Together,$phellogen$,$phellem$,and $phelloderm$ constitute the $periderm$.

(A) In dicot roots,the pericycle is the layer of cells located between the endodermis and the vascular tissue.
During secondary growth,the pericycle cells become meristematic and contribute to the formation of lateral roots (branch roots).
Additionally,in dicot roots,the pericycle also participates in the formation of the vascular cambium and the cork cambium (phellogen) during secondary growth.

(A) Medullary vascular bundles are vascular bundles that are located in the pith (medulla) region of the stem.
These are considered an anomalous secondary growth feature.
$Bignonia$ is a classic example of a plant that exhibits anomalous secondary growth,where vascular bundles are found in the pith region in addition to the normal ring of vascular bundles.

(D) In dicot roots,the vascular cambium is secondary in origin.
It develops from the conjunctive parenchyma cells located just below the phloem bundles.
Additionally,the pericycle cells located outside the protoxylem also become meristematic.
These two groups of cells join to form a continuous wavy ring of vascular cambium.

(D) Secondary growth in dicot stems involves the formation of a continuous cambial ring.
Initially,the intrafascicular cambium (present within vascular bundles) and the interfascicular cambium (formed from medullary rays) join to form a complete ring in the stelar region.
Additionally,the cork cambium (phellogen) develops in the cortical region to produce secondary cortex and cork.
Therefore,secondary growth involves the activity of cambium in both the stelar region (vascular cambium) and the cortical region (cork cambium).

(A) Cambium is a lateral meristem responsible for secondary growth in plants.
Secondary growth leads to an increase in the girth or diameter of the stem and root.
Therefore,cambium causes growth in the circumference or width of the plant body.
Since both circumference and width (diameter) refer to the same type of growth,and the question asks for the primary effect,it increases the girth.

(B) The peripheral region of the secondary xylem is lighter in color and is known as the sap wood or $Alburnum$.
It is physiologically active and is involved in the conduction of water and minerals from the root to the leaf.
In contrast,the central,darker,and harder region is called heartwood or $Duramen$.

(A) The cork cambium, also known as $phellogen$, originates from the outer layers of the cortex during secondary growth.
It undergoes periclinal divisions to produce cells on both sides.
It cuts off cells towards the outside, which differentiate into cork or $phellem$.
It cuts off cells towards the inside, which differentiate into secondary cortex or $phelloderm$.
Together, $phellogen$, $phellem$, and $phelloderm$ are collectively known as periderm.

(C) The secondary cortex is known as $Phelloderm$.
The cork cambium is known as $Phellogen$.
The cork is known as $Phellem$.
Therefore,the correct sequence for secondary cortex,cork cambium,and cork is $Phelloderm$,$Phellogen$,and $Phellem$ respectively.

(D) In dicot roots,secondary growth occurs due to the activity of vascular cambium and cork cambium.
Cork cambium,also known as phellogen,develops in the older roots.
It arises from the dedifferentiation of the outer cells of the $Pericycle$.
These cells undergo tangential divisions to form the cork (phellem) on the outside and the secondary cortex (phelloderm) on the inside.

(D) The $Periderm$ is formed during the secondary growth in dicot stems. The cork cambium or $Phellogen$ cuts off cells on both sides. The cells cut off towards the outer side differentiate into cork or $Phellem$,while the cells cut off towards the inner side differentiate into secondary cortex or $Phelloderm$. Collectively,$Phellem$,$Phellogen$,and $Phelloderm$ are known as $Periderm$.

(C) Secondary growth is the increase in girth or diameter of the plant body due to the activity of lateral meristems (vascular cambium and cork cambium).
In $Dicot$ stems,$Dicot$ roots,and $Gymnosperms$,secondary growth occurs due to the presence of vascular cambium.
In $Monocot$ stems,the vascular bundles are scattered and closed (i.e.,they lack cambium),which prevents the formation of secondary tissues. Therefore,secondary growth is absent in $Monocot$ stems.

(D) The growth in the circumference or girth of stems and roots is known as secondary growth.
Secondary growth is primarily facilitated by the activity of lateral meristems.
Cambium,specifically the vascular cambium,is a type of lateral meristematic tissue that divides to produce secondary xylem towards the inside and secondary phloem towards the outside.
This continuous production of secondary vascular tissues leads to an increase in the diameter (girth) of the plant axis.
Therefore,the cambium is responsible for the increase in girth.

(A) The vascular cambium is a lateral meristem that is responsible for secondary growth in stems.
During secondary growth,the cambium cells divide periclinally.
The cells cut off towards the inner side differentiate into secondary xylem,which is commonly known as wood.
Wood fibres are a component of secondary xylem (wood),thus they are formed from cells cut off by the cambium on its inner side.
Bast fibres are associated with secondary phloem,which is formed on the outer side of the cambium.
Sieve tubes and companion cells are also components of the phloem.

(A) Cork cells are dead cells that possess thick walls heavily impregnated with a waxy substance called suberin. This makes them impervious to water and gases,providing protection to the inner tissues of the plant.

(B) In a dicot stem,the vascular cambium is located between the primary xylem and primary phloem.
During secondary growth,the vascular cambium divides to produce secondary xylem towards the inner side and secondary phloem towards the outer side.
Since the cambium is constantly adding new cells to the inner side,the most recently formed (youngest) layer of secondary xylem is always found immediately adjacent to the inner surface of the vascular cambium.

(D) . Annual rings are formed due to the variation in the climatic conditions of a region. In temperate regions,there is a clear distinction between the spring season and the autumn season. During spring,the cambium is very active and produces a large number of xylem elements with wider vessels (spring wood),whereas in autumn,the cambium is less active and produces fewer xylem elements with narrow vessels (autumn wood). This seasonal variation results in the formation of distinct annual rings.

(C) In dicot roots, secondary growth occurs due to the activity of the vascular cambium and the cork cambium $(phellogen)$.
As the secondary growth progresses over two or three years, the increasing girth of the root exerts pressure on the outer tissues.
The epidermis and the cortex are gradually crushed and eventually sloughed off due to the formation of the periderm (cork, cork cambium, and secondary cortex) and the continuous expansion of the vascular tissues.
Therefore, the cortex is largely lost as the root matures.

(A) Growth rings $(Annual\ rings)$ are formed due to the differential activity of the cambium throughout the year.
In temperate regions,the climate is seasonal,leading to distinct periods of active and inactive cambial growth,which results in clearly demarcated annual rings.
Shimla is located in a temperate region,whereas Bombay,Madras,and Calcutta are in tropical regions where climatic variations are less pronounced,leading to indistinct growth rings.

(B) In a dicot tree,the secondary xylem is differentiated into two regions: heartwood and sapwood.
$1$. Heartwood (duramen) is the central,darker,and harder part of the secondary xylem. It consists of dead elements with highly lignified walls and is non-functional in water conduction.
$2$. Sapwood (alburnum) is the peripheral,lighter-colored,and softer part of the secondary xylem. It consists of living cells and is responsible for the conduction of water and minerals from the roots to the leaves.
Therefore,the functional xylem in a dicot tree is the sapwood.

(D) In a dicot stem, the primary protective tissue is the $Epidermis$.
As the plant undergoes secondary growth, the epidermis is replaced by the $Cork$ (also known as $Phellem$), which acts as the secondary protective tissue.
Therefore, the external protective tissues of a dicot stem are the $Epidermis$ (primary) and the $Cork$ (secondary).

(A) Cork cambium,also known as phellogen,is a lateral meristem that develops during secondary growth in plants.
Since it originates from differentiated permanent tissues (like cortical cells) during the process of secondary growth,it is classified as a secondary meristem.
Apical and intercalary meristems are types of primary meristems responsible for the primary growth (increase in length) of the plant.

(B) The $Phellogen$ (cork cambium) is a meristematic tissue that develops in the cortex region during secondary growth.
It undergoes periclinal division to produce $Phellem$ (cork) on the outer side and $Phelloderm$ (secondary cortex) on the inner side.
Therefore, the cambium responsible for the production of cork is $Phellogen$.

(D) The differentiation of bark,sapwood,and heartwood is a characteristic feature of dicotyledonous trees that undergo secondary growth.
$Ashoka$,$Neem$,and $Mango$ are dicotyledonous plants that exhibit secondary growth,leading to the formation of wood and bark.
$Date$ $palm$ ($Phoenix$ $dactylifera$) is a monocotyledonous plant.
Monocots do not possess a vascular cambium and therefore do not exhibit secondary growth.
Consequently,they do not form bark,sapwood,or heartwood.

(A) Growth rings, also known as $annual\ rings$, are formed due to the differential activity of the vascular cambium. In temperate regions, the cambium is more active during the spring season and produces a large number of xylem elements with wider vessels, known as $spring\ wood$ or $early\ wood$. In winter, the cambium is less active and produces fewer xylem elements with narrow vessels, known as $autumn\ wood$ or $late\ wood$. The band of $spring\ wood$ and $autumn\ wood$ formed in a year constitutes an $annual\ ring$.

(D) Generally,monocots do not exhibit secondary growth because they lack a vascular cambium. However,some arborescent monocots,such as $Yucca$ and $Dracaena$,are exceptions. In these plants,secondary growth occurs due to the formation of a secondary meristem in the cortex,which produces secondary vascular bundles and parenchyma,leading to an increase in the girth of the stem.

(B) Secondary growth in dicot stems is primarily caused by the activity of lateral meristems.
These include the vascular cambium,which produces secondary xylem and secondary phloem,and the cork cambium (phellogen),which produces periderm (cork and secondary cortex).
Apical meristems are responsible for primary growth (increase in length),whereas lateral meristems are responsible for secondary growth (increase in girth).

(C) Annual rings are formed by the activity of the vascular cambium,which produces secondary xylem towards the inner side and secondary phloem towards the outer side.
However,the annual ring specifically refers to the concentric layers of secondary xylem formed during a single growing season (spring wood and autumn wood).
Secondary phloem is crushed and does not contribute to the formation of the distinct annual ring structure used for age estimation.
Therefore,the annual ring is primarily composed of secondary xylem.

(A) Secondary growth is the increase in the thickness or girth of the plant body.
It is primarily caused by the activity of the vascular cambium and the cork cambium.
In dicot stems,the vascular cambium is present between the xylem and phloem,which allows for the production of secondary xylem and secondary phloem,leading to secondary growth.
Monocot stems lack a vascular cambium,and therefore,they do not exhibit secondary growth.
While roots of dicots also undergo secondary growth,the question specifically refers to the standard occurrence in stems,making the dicot stem the most appropriate answer.

(C) Dendrochronology is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed.
In temperate regions,trees produce one growth ring per year due to the seasonal activity of the vascular cambium.
By counting these annual rings in the main stem,scientists can determine the age of the tree and study past climatic conditions.

(A) Tyloses are balloon-like outgrowths of parenchyma cells that protrude into the lumen of a vessel or tracheid through the pits.
They are typically found in the $Secondary \ xylem$ of older trees,where they block the vessels and help in the formation of heartwood.
They develop as a response to injury or infection to prevent the spread of pathogens.

(B) Fusiform initials are elongated cells in the vascular cambium that divide to produce the axial system of the secondary xylem and secondary phloem. These include tracheary elements (tracheids and vessels),fibres,and axial parenchyma. Therefore,the correct option is $B$.

(B) In the primary stem of dicotyledonous plants,the vascular bundles contain a layer of meristematic cells situated between the primary xylem and primary phloem.
This specific layer is known as the intrafascicular cambium or fascicular cambium.
It is responsible for the production of secondary xylem and secondary phloem during secondary growth.
Procambium is the precursor tissue that gives rise to the vascular bundles,while cork cambium is involved in the formation of the periderm (bark).

(D) The correct answer is $D$. Annual rings are formed due to the differential activity of the vascular cambium,which is influenced by seasonal variations in climate (such as the difference between spring and autumn). In desert regions,the climate remains relatively uniform throughout the year,lacking the distinct seasonal changes required to produce clearly defined annual rings. Therefore,trees growing in the desert do not show distinct annual rings.

(D) . The bark of a tree includes the periderm and the secondary phloem. If the bark is removed (girdling),the phloem tissue is destroyed. Since the phloem is responsible for the translocation of food (sucrose) from the leaves to the roots,its destruction stops the supply of nutrients to the root system. Consequently,the roots die due to starvation,and because the roots are unable to absorb water and minerals without energy,the entire tree eventually dies.

(B) Knots are formed when wounds on the stem undergo rapid cell division. The wound is covered by new cells,but the healing process is irregular or incomplete,leading to the development of a knot-like structure in the mature stem.

(A) Secondary growth in dicot roots and stems is primarily facilitated by the activity of the vascular cambium.
In stems,the intrafascicular cambium and interfascicular cambium join to form a complete ring of vascular cambium.
In roots,the vascular cambium originates from the tissue located just below the phloem bundles and above the protoxylem.
Therefore,the formation of the vascular cambium is the essential prerequisite for the initiation of secondary growth.

(A) As a tree grows older,secondary growth occurs due to the activity of the vascular cambium. This process produces secondary xylem towards the inner side. The older,central part of the secondary xylem becomes physiologically inactive,dark,and hard due to the deposition of tannins,resins,and oils,which is known as heartwood $(duramen)$. While heartwood provides mechanical support,the sapwood $(alburnum)$ is the peripheral,physiologically active part of the secondary xylem that conducts water and minerals. In older trees,the volume of heartwood increases significantly as more sapwood is converted into heartwood over time.