Secondary growth Questions in English

(A) The periderm consists of three layers: phellem (cork),phellogen (cork cambium),and phelloderm.
The phellogen (cork cambium) is a meristematic tissue that develops in the cortex,epidermis,or phloem.
It produces phellem (cork) towards the outside and phelloderm (secondary cortex) towards the inside.
Therefore,the entire periderm is produced by the activity of the cork cambium (phellogen).

(A) Spring wood and autumn wood formed in a single year together constitute an annual ring.
The spring wood,also known as $Early \ wood$,is lighter in colour and has a lower density because the cambium is very active during the spring season.
The autumn wood,also known as $Late \ wood$,is darker in colour and has a higher density due to the reduced activity of the cambium.
Therefore,the light-coloured part of an annual ring is the $Early \ wood$.

(D) During secondary growth in dicot stems,the vascular cambium produces secondary xylem towards the inside and secondary phloem towards the outside. In addition to these,the vascular cambium also produces some narrow bands of parenchymatous cells that pass through the secondary xylem and secondary phloem in a radial direction. These are known as secondary medullary rays.

(C) The secondary meristem,such as the vascular cambium and cork cambium,is responsible for increasing the girth or diameter of the plant stem and root. This increase in thickness is known as radial growth or secondary growth.

(B) Heartwood,also known as $duramen$,is the central,non-functional part of the secondary xylem.
Statement $I$ is true because heartwood does not conduct water due to the deposition of organic compounds.
Statement $II$ is false because alburnum refers to sapwood,not heartwood.
Statement $III$ is false because heartwood is dark in colour but very hard and durable,not soft.
Statement $IV$ is true because the tracheary elements in heartwood are filled with tannins,resins,oils,gums,and aromatic substances,which make it resistant to microbial attack.

(D) During secondary growth,the phellogen (cork cambium) acts as a meristematic tissue that cuts off cells on both sides.
The cells produced on the outer side differentiate into cork (also known as phellem),which is impervious to water due to the deposition of suberin.
The cells produced on the inner side differentiate into secondary cortex (also known as phelloderm),which consists of parenchymatous cells.
Therefore,$A$ is cork/phellem and $B$ is secondary cortex.

(B) Tyloses are balloon-like outgrowths of xylem parenchyma cells that penetrate into the lumen of adjacent xylem vessels through pits.
These structures are characteristic of heartwood,where they block the vessel cavity,rendering the wood more durable and resistant to decay.
They are not typically found in functional sapwood.

(D) In a dicot root,secondary growth involves the formation of a cork cambium (phellogen) in the cortical region.
This cork cambium produces cork (phellem) towards the outside and secondary cortex (phelloderm) towards the inside.
Since the cork cambium originates in the cortex (which is outside the endodermis),the resulting cork layer is also located outside the endodermis.
Furthermore,the cork is situated outside the primary phloem,as the primary phloem is located deeper within the root,just outside the vascular cambium.

(A) The vascular cambium ring becomes active and begins to cut off new cells both towards the inner and the outer sides.
Cells cut off towards the pith (inner side) mature into secondary xylem.
Cells cut off towards the periphery (outer side) mature into secondary phloem.

(C) In dicot stems,the cells of cambium present between the primary xylem and primary phloem are known as intrafascicular cambium.
These cells remain meristematic and contribute to secondary growth.
The cells of medullary rays,adjoining these intrafascicular cambium,become meristematic to form the interfascicular cambium.
Together,these form a continuous ring of cambium.

(A) After certain years of growth,the xylem elements of the stems of a number of trees develop a dark brown coloration,especially in the central or innermost layers.
This region comprises dead elements with highly lignified walls and is called heartwood or duramen.
It is present in the inner region of secondary wood.

(C) In a woody dicot stem,the arrangement of tissues from the outer side to the inner side is as follows:
$1.$ $Phellem$ (Cork): This is the outermost layer formed by the phellogen.
$2.$ $Secondary$ $cortex$ $(Phelloderm)$: This is formed by the phellogen towards the inner side.
$3.$ $Secondary$ $phloem$: This is formed by the vascular cambium towards the outer side.
$4.$ $Autumn$ $wood$: This is a part of the secondary xylem formed by the vascular cambium towards the inner side.
Therefore,the correct sequence from outer to inner is $IV, I, III, II$.

(B) Annual growth rings are formed due to the differential activity of the vascular cambium,which is influenced by seasonal variations in climate.
In temperate regions,there are distinct seasonal changes,leading to the formation of clear annual rings.
In tropical evergreen forests,the climate remains relatively uniform throughout the year without significant seasonal fluctuations.
Consequently,the activity of the vascular cambium remains constant,and distinct growth rings are either absent or not sharply demarcated.

(B) The correct answer is $IV$.
Heartwood is the central,innermost part of the secondary xylem in old trees. It is dark brown due to the deposition of organic compounds like tannins,resins,oils,gums,aromatic substances,and essential oils. These substances make it hard,durable,and resistant to the attacks of microorganisms and insects. It consists of dead elements with highly lignified cell walls. In contrast,the peripheral part of the secondary xylem is known as sapwood,which is lighter in color and involved in the conduction of water and minerals. Therefore,statement $IV$ (It is the peripheral part) does not describe heartwood.

(B) In tropical regions, there is no sharp distinction between seasons, which leads to a continuous and uniform activity of the cambium throughout the year.
In diffused porous wood, the vessels are of similar size and are distributed uniformly throughout the growth ring, including both early wood and late wood.
This is a characteristic feature of plants growing in tropical climates, such as $Syzygium \text{ } cumini$.

(C) The vascular cambium is generally more active on the inner side than on the outer side.
As a result,the amount of secondary xylem produced towards the center is significantly more than the secondary phloem produced towards the periphery.
This differential activity leads to the formation of a compact mass of secondary xylem,which constitutes the bulk of the wood.

(C) The cork,also known as $phellem$,is a protective tissue formed during secondary growth.
Its cells are dead and have walls that are heavily thickened with $suberin$,a fatty substance.
$Suberin$ is hydrophobic in nature,which makes the cork cells impervious to water and gases,thereby preventing water loss from the plant body.

(A) lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the bark of woody stems and roots of dicotyledonous flowering plants.
In the provided diagram:
$A$ points to the Epidermis (or the remains of the epidermis).
$B$ points to the Cork cambium (phellogen),which is responsible for producing the complementary cells of the lenticel.
$C$ points to the Secondary cortex (phelloderm).
Therefore,the correct labeling is $A-$ Epidermis,$B-$ Cork cambium,$C-$ Secondary cortex.

(A) The vascular cambium in the stem is considered to be partly primary and partly secondary in origin.
$1$. The intrafascicular cambium,which is present between the xylem and phloem of the vascular bundles,is primary in origin as it originates from the procambium.
$2$. The interfascicular cambium,which develops from the medullary rays during secondary growth,is secondary in origin.
Therefore,the complete vascular cambium ring is formed by the combination of both primary and secondary meristematic tissues.

(D) During secondary growth in dicot stems,the vascular cambium becomes active and produces secondary xylem towards the inner side and secondary phloem towards the outer side.
As the secondary xylem accumulates,it exerts pressure on the primary xylem,which remains more or less intact in the center of the stem.
Conversely,the primary phloem is pushed outward and eventually gets crushed due to the continuous formation and accumulation of secondary phloem and secondary xylem.
Therefore,statement $I$ is correct because primary phloem is crushed,but secondary phloem is generally not crushed as it is newly formed. However,in the context of standard biology questions,statement $I$ is often considered correct regarding the crushing of primary phloem,and statement $II$ is correct regarding the primary xylem. Since both statements are factually correct,there is no 'wrong' statement among the choices provided.

(C) $I.$ Annual rings are indeed formed due to seasonal variations in the activity of the vascular cambium,which is influenced by environmental conditions. This statement is correct.
$II.$ During spring (favorable conditions),the cambium is very active and produces a large number of xylem elements with vessels having wider cavities. This statement is correct.
$III.$ In autumn or winter (water deprivation/less favorable conditions),the cambium is less active and produces fewer xylem elements with narrow vessels and thicker walls. This statement is correct.
$IV.$ While heartwood (older wood) is generally darker than sapwood (newer wood) due to the deposition of organic compounds like tannins,resins,and oils,it is not a universal rule that wood formed in previous years is always darker than newer wood in all species. However,in the context of standard biology curriculum regarding annual rings,statements $I, II,$ and $III$ are the primary characteristics of seasonal wood formation.

(D) Generally,secondary growth does not occur in monocot stems because they lack a vascular cambium.
However,there are some exceptions to this rule,such as $Yucca$ and $Aloe$,which exhibit anomalous secondary growth in their stems due to the activity of a secondary meristem.

(D) The woody axis or the increase in girth (diameter) of flowering plants is caused by secondary growth.
Secondary growth is facilitated by the activity of secondary meristems,which include the vascular cambium and cork cambium.
Apical meristem and intercalary meristem are both types of primary meristems,which are responsible for the primary growth or increase in the length of the plant axis.

(B) The presence of cambium in the vascular bundles allows them to undergo secondary growth. These vascular bundles are known as $Open$ vascular bundles. The cambium is a meristematic tissue that divides to form secondary xylem and secondary phloem,which are secondary tissues.

(A) The tissue that participates in secondary growth is the lateral meristem.
Lateral meristems,such as the vascular cambium and cork cambium,are responsible for increasing the girth or diameter of the plant body.
In contrast,apical and intercalary meristems are responsible for the primary growth,which involves increasing the length of the plant.

(A) The cambial ring is generally more active on the inner side than on the outer side.
As a result,it produces a larger amount of secondary xylem towards the center and a smaller amount of secondary phloem towards the periphery.
This differential activity is responsible for the formation of the bulk of the wood in plants.

(B) In a dicot stem,the interfascicular cambium is formed by the dedifferentiation of the parenchymatous cells of the medullary rays located between the vascular bundles. These cells regain their meristematic property to form a continuous cambial ring.

(C) Wood is technically defined as the secondary xylem produced by the activity of the vascular cambium in dicotyledonous plants. During secondary growth,the vascular cambium cuts off cells towards the inner side,which mature into secondary xylem,forming the bulk of the woody stem.

(B) In temperate regions,the climatic conditions are not uniform throughout the year. During the spring season,the cambium is very active and produces a large number of xylem elements with vessels having wider cavities,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. One annual ring consists of one band of spring wood and one band of autumn wood formed in a single year.

(C) Growth rings are formed due to the differential activity of the vascular cambium in response to seasonal variations in climate.
In temperate regions like Shimla,the climate changes significantly throughout the year,leading to the formation of distinct spring wood (early wood) and autumn wood (late wood),which together form a growth ring.
In contrast,tropical and coastal regions like Mumbai,Chennai,and Kolkata experience a relatively uniform,hot,and humid climate throughout the year,which does not result in the formation of distinct growth rings.

(A) Heartwood is the central,non-functional part of the secondary xylem. It consists of dead elements with highly lignified walls. Due to the deposition of organic compounds like tannins,resins,oils,gums,aromatic substances,and essential oils in the central layers of the stem,it becomes hard,durable,and resistant to the attacks of microorganisms and insects. Its primary function is to provide mechanical support to the stem.

(D) The heartwood consists of dead elements with highly lignified walls. In the heartwood,the xylem vessels and tracheids are blocked by the deposition of organic compounds like tannins,resins,oils,gums,aromatic substances,and essential oils.
Additionally,tyloses (balloon-like outgrowths of xylem parenchyma cells into the vessel lumen through pit cavities) further block the xylem elements,preventing the conduction of water.

(D) The periderm is composed of three layers: phellem (cork),phellogen (cork cambium),and phelloderm (secondary cortex).
Since phelloderm is another name for the secondary cortex,both options $A$ and $B$ are correct.
Therefore,the correct answer is $D$.

(A) Both heartwood and sapwood are regions of secondary xylem.
Sapwood is the peripheral region of secondary xylem that is involved in the conduction of water and minerals.
Heartwood is the central,dark-colored region of secondary xylem that does not conduct water due to the deposition of organic compounds like tannins,resins,oils,gums,aromatic substances,and essential oils in the vessels.
These substances make the heartwood hard,durable,and resistant to the attacks of microorganisms and insects.

(B) Lenticels are lens-shaped openings found in the periderm of woody stems that allow for gaseous exchange.
Bulliform cells are specialized epidermal cells in grasses that help in leaf rolling to reduce water loss.
Pneumatophores are specialized roots found in plants growing in swampy areas,which help in respiration.
Trichomes are epidermal outgrowths on the stem that primarily serve to reduce transpiration and protect the plant.

(C) Bark is a non-technical term used to describe all tissues located exterior to the vascular cambium.
It includes secondary phloem,primary phloem,cortex,pericycle,and the periderm (cork cambium,cork,and secondary cortex).
Therefore,all tissues outside the vascular cambium are collectively referred to as bark.

(A) In dicot roots,secondary growth occurs due to the activity of the vascular cambium and the cork cambium.
Both vascular cambium and cork cambium are secondary meristems that develop only after the completion of primary growth.
Therefore,the statement that both are responsible for secondary growth is correct.

(B) In dicot roots,the cells of the pericycle undergo division to initiate the formation of lateral roots.
Additionally,during secondary growth,the pericycle cells also contribute to the formation of the cork cambium (phellogen) in the root.

(D) The vascular cambium is a lateral meristem responsible for secondary growth in dicotyledonous plants.
It divides periclinally to produce secondary xylem towards the inner side and secondary phloem towards the outer side.
Additionally,it produces parenchyma cells that form medullary rays (also known as vascular rays) which facilitate radial conduction of water and food.
Therefore,it cuts off secondary xylem,secondary phloem,and medullary rays.

(C) The secondary meristem in the stelar region is the vascular cambium. The vascular cambium is responsible for the production of secondary vascular tissues. It cuts off cells towards the inner side to form secondary xylem (wood) and towards the outer side to form secondary phloem. Alburnum is another term for sapwood,which consists of functional secondary xylem. Duramen is heartwood,which is non-functional secondary xylem. Therefore,the derivatives of the vascular cambium include secondary xylem (which forms alburnum and duramen) and secondary phloem.

(C) During secondary growth,the vascular cambium produces secondary xylem towards the inside and secondary phloem towards the outside.
As new layers of secondary phloem are continuously added by the vascular cambium,the older layers are pushed further outward.
Therefore,the oldest secondary phloem is located at the periphery,just below the pericycle (or primary phloem),while the youngest secondary phloem is found just outside the vascular cambium.

(C) In dicot stems,the vascular cambium is responsible for secondary growth.
As the vascular cambium divides,it adds secondary xylem towards the inner side and secondary phloem towards the outer side.
The cells of the secondary xylem that are produced most recently are located closest to the vascular cambium.
Therefore,the youngest layer of secondary xylem is found just inside the vascular cambium,while the oldest layer is found near the primary xylem or pith.

(D) . Heartwood (duramen) is the central,dead,and dark-colored part of the secondary xylem,which is highly durable due to the deposition of tannins,resins,and oils. This statement is correct.
$B$. Tyloses are outgrowths of xylem parenchyma cells into the lumen of vessels through pits,appearing as balloon-like structures. This statement is correct.
$C$. Late wood (autumn wood) is formed during the autumn or winter season when cambium activity is less,resulting in narrower and darker vessels. Spring wood is formed during the spring season. Therefore,statement $C$ is incorrect.

(C) Cork cambium,also known as phellogen,is a secondary meristematic tissue. It develops in the extrastelar region of the stem during secondary growth. It arises due to the process of dedifferentiation of the cortical cells (parenchyma cells) located just below the epidermis.

(D) The activity of the vascular cambium is highly dependent on environmental and physiological factors. Factors such as $A$,$B$,and $C$ directly influence the rate of cambial activity,which leads to the formation of annual rings in temperate regions. However,leaf orientation does not have a direct or significant influence on the seasonal activity of the vascular cambium.

(C) The first step in the initiation of secondary growth in a dicot stem is the dedifferentiation of the parenchymatous cells of the medullary rays located between the vascular bundles. These cells become meristematic and form the interfascicular cambium. This newly formed interfascicular cambium then connects with the existing intrafascicular cambium to form a complete,continuous cambial ring.

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

(A) Secondary phloem is formed by the activity of the vascular cambium during secondary growth. It is a secondary permanent tissue. Unlike primary phloem,which differentiates into protophloem and metaphloem,secondary phloem does not show such a distinction. Therefore,the statement that it arises due to the activity of the procambium is incorrect,as the procambium is responsible for the formation of primary vascular tissues.

(C) During secondary growth,the cork cambium (phellogen) produces thin-walled,loosely arranged parenchymatous cells on its outer side instead of cork cells at certain places. These are called complementary cells. The rapid division and increase in the number of these complementary cells exert pressure on the epidermis,causing it to rupture and form a lens-shaped opening known as a lenticel.

(D) The Assertion is incorrect because the oldest layer of sapwood is found near the heartwood,not just outside the vascular cambium. The youngest layer of sapwood is located just outside the vascular cambium.
The Reason is incorrect because sapwood is the peripheral,living part of the secondary xylem,while the central part of the stem is occupied by heartwood (duramen),which is non-conducting and dead.