Secondary growth Questions in English

(C) Lenticels are lens-shaped openings found in the bark of woody stems and roots.
They develop due to the activity of $Phellogen$ $(cork\ cambium)$.
$Phellogen$ cuts off cells towards the outside,which are loosely arranged and are known as complementary cells.
These cells exert pressure on the epidermis,causing it to rupture and form the lenticel.

(C) In a stratified cambium,the fusiform initials are relatively short and are arranged in horizontal tiers. This arrangement is characteristic of certain plants,such as some legumes,where the ends of the cells in one tier align with the ends of the cells in the adjacent tier,rather than overlapping.

(C) The intrafascicular cambium is the layer of meristematic cells that is present within the vascular bundles of dicotyledonous stems.
It is located between the primary xylem and the primary phloem.
During secondary growth,this cambium becomes active and contributes to the formation of secondary vascular tissues.

(A) The vascular cambium consists of two types of initials: fusiform initials and ray initials.
Fusiform initials give rise to the axial system,which includes tracheids,vessels,xylem fibres,phloem fibres,sieve tubes,and companion cells.
Ray initials give rise to the radial system,which forms the vascular rays (also known as xylem rays or phloem rays).
Therefore,vascular rays originate from the ray initials of the cambium.

(B) In older dicot stems,the secondary xylem in the central or innermost region becomes dark brown due to the deposition of organic compounds like tannins,resins,oils,gums,aromatic substances,and essential oils.
These substances make the wood hard,durable,and resistant to the attacks of microorganisms and insects.
This region is known as heartwood or duramen.
It does not conduct water but provides mechanical support to the stem.

(D) The activity of the cambium is influenced by seasonal variations.
In the spring season,the cambium is very active and produces a large number of xylary elements having vessels with wider cavities,forming spring wood.
In contrast,during the summer or autumn season,the activity of the cambium is less,resulting in the production of fewer xylary elements with narrow vessels,forming autumn wood.
Therefore,in summer,the cambium is less active.

(C) Secondary growth in dicotyledonous plants is primarily driven by the activity of the vascular cambium.
$1$. The vascular cambium is a lateral meristematic tissue composed of thin-walled,rectangular cells.
$2$. These cells are highly active and divide to produce secondary xylem towards the inside and secondary phloem towards the outside.
$3$. This process increases the girth or diameter of the stem and root,which is known as secondary growth.
Therefore,the correct answer is $C$ (Cambium).

(B) In plants belonging to the family Cruciferae (Brassicaceae),the increase in girth of stems and roots is known as secondary growth.
Secondary growth is primarily caused by the activity of the vascular cambium.
The vascular cambium produces secondary xylem towards the inner side and secondary phloem towards the outer side,which leads to an increase in the diameter of the plant axis.

(D) The vascular cambium is a lateral meristematic tissue responsible for secondary growth in plants.
It undergoes periclinal divisions to cut off cells towards the inner side and the outer side.
The cells cut off towards the inner side differentiate into secondary xylem.
The cells cut off towards the outer side differentiate into secondary phloem.
Therefore,the vascular cambium produces secondary xylem and secondary phloem.

(B) Cork cells,also known as phellem,are formed during secondary growth in plants.
These cells have thick walls that are impregnated with a waxy,hydrophobic substance called $Suberin$.
$Suberin$ deposition makes the cell walls impervious to water and gases,which protects the inner tissues of the plant from desiccation and mechanical injury.

(D) The correct answer is $D$. Heartwood (duramen) is the central,non-functional,dead part of the secondary xylem in older trees. Its primary function is to provide mechanical support and structural strength to the stem. It does not participate in the conduction of water or minerals,as those functions are performed by the sapwood (alburnum). Therefore,if the heartwood is removed or decays,the plant can still survive as the sapwood remains intact to conduct water and nutrients.

(C) Ring bark is formed when the cork cambium (phellogen) develops in the form of a complete ring around the stem. This results in the formation of a continuous layer of bark that can peel off in large sheets. This type of bark is characteristic of $Betula$ $utilis$ (commonly known as $Bhojpatra$).

(A) An annual growth ring is formed by the activity of the vascular cambium in temperate regions.
It consists of two distinct zones: the early wood (spring wood) and the late wood (autumn wood).
The early wood is formed during the spring season and consists of wider,thin-walled xylem vessels.
The late wood is formed during the autumn season and consists of narrower,thick-walled xylem vessels.
Therefore,each annual ring is composed of an inner layer (early wood) and an outer layer (late wood).

(A) 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 inside and secondary phloem towards the outside. Therefore,the newly formed (youngest) secondary phloem cells are always added immediately outside the vascular cambium,while the older secondary phloem layers are pushed further outward towards the primary phloem.

(A) Cork,also known as phellem,is produced by the activity of the cork cambium,which is technically called the phellogen.
The phellogen is a secondary meristem that develops in the cortex region of the stem during secondary growth.
It cuts off cells on both sides: the cells cut off towards the outside differentiate into cork (phellem),while the cells cut off towards the inside differentiate into secondary cortex (phelloderm).
Together,phellogen,phellem,and phelloderm are collectively known as periderm.

(A) Lenticels are small,lens-shaped openings or pores present on the surface of the bark of woody stems and roots.
They are formed due to the activity of the phellogen (cork cambium) which produces loosely arranged parenchymatous cells called complementary cells instead of cork cells at certain regions.
These pores allow for the exchange of gases between the internal tissues of the stem and the outer atmosphere,thus acting as aerating pores.

(B) Heartwood,also known as duramen,is the inner,darker,and harder region of the secondary xylem in older trees.
It consists of dead elements with highly lignified walls.
It is filled with organic compounds like tannins,resins,oils,gums,aromatic substances,and essential oils,which make it resistant to microbial attacks and insects.
It does not conduct water but provides mechanical support to the stem.

(B) Annual rings are formed due to the differential activity of the vascular cambium,which is influenced by seasonal variations in climate.
In temperate regions,there is a clear distinction between seasons (spring and autumn),leading to the formation of distinct annual rings.
In tropical regions,the climate remains relatively uniform throughout the year,meaning the cambium remains active almost continuously.
Consequently,distinct annual rings are not formed in trees growing in tropical evergreen forests,making it impossible to determine their age using this method.

(B) The correct answer is $(B)$.
Commercial cork is obtained from the bark of the Oak tree,specifically $(Quercus\ suber)$.
The cavities of the cork cells are filled with air,which makes the cork lightweight and provides excellent thermal insulating properties.
This material is widely used for making bottle stoppers due to its elasticity and impermeability to liquids and gases.

(A) Lenticels are lens-shaped openings found in the bark of woody stems and roots.
These pores allow for the exchange of gases between the internal tissues of the plant and the external atmosphere.
They are formed during secondary growth when the phellogen (cork cambium) produces loosely arranged parenchyma cells instead of cork cells at certain locations.

(B) Lenticels are lens-shaped openings found in the bark of older woody stems. They are formed during secondary growth when the cork cambium (phellogen) produces loosely arranged parenchyma cells instead of cork cells at certain spots. These structures facilitate the exchange of gases between the internal tissues of the stem and the outer atmosphere.

(D) Secondary growth refers to the increase in the girth or diameter of the plant axis.
This process is primarily driven by the activity of lateral meristems, specifically the $Vascular cambium$ and the $Cork cambium$.
The $Vascular cambium$ is responsible for the production of secondary xylem and secondary phloem, which significantly contributes to the increase in the diameter of the stem and root.
Therefore, the primary cause of secondary growth is the activity of the $Vascular cambium$.

(D) Secondary meristems,such as the vascular cambium and cork cambium (phellogen),are responsible for secondary growth in plants.
$1$. The vascular cambium produces secondary xylem (wood) and secondary phloem.
$2$. The cork cambium (phellogen) produces phellem (cork) on the outer side and phelloderm (secondary cortex) on the inner side.
Since all the listed options are products of secondary meristematic activity,the correct answer is $D$.

(A) Growth rings,also known as annual rings,are formed due to the differential activity of the vascular cambium throughout the seasons.
In temperate regions,the cambium is more active in spring and less active in autumn,resulting in the formation of spring wood and autumn wood,respectively.
Together,these two layers constitute one annual ring,which represents one year of growth.
Therefore,by counting the number of annual rings in a tree trunk,the age of the tree can be determined.

(B) The cork cambium $(phellogen)$,the cork $(phellem)$,and the secondary cortex $(phelloderm)$ are collectively known as the $periderm$.
$Phellem$ is formed on the outside,while $phelloderm$ is formed on the inside by the $phellogen$.
$Periderm$ acts as a secondary protective tissue in plants.

(D) The cork cambium is a lateral meristem that develops in the cortex region of the stem during secondary growth.
It is scientifically known as the $Phellogen$.
$Phellem$ refers to the cork,$Phelloderm$ refers to the secondary cortex,and $Periderm$ is the collective term for $Phellem$,$Phellogen$,and $Phelloderm$ together.

(C) Secondary meristems are those that develop from permanent tissues through the process of dedifferentiation.
$1$. Cork cambium (phellogen) is a classic example of a secondary meristem because it originates from the cortical cells or pericycle during secondary growth.
$2$. Phelloderm is a permanent tissue formed by the activity of the cork cambium.
$3$. Primary cambium and promeristem are examples of primary meristems as they are derived directly from the embryonic cells.
Therefore,the correct answer is $C$.

(B) The increase in the girth or diameter of a dicot stem is known as secondary growth.
This process is primarily mediated by the activity of the lateral meristems,specifically the vascular cambium.
The vascular cambium produces secondary xylem towards the inner side and secondary phloem towards the outer side,which leads to an increase in the thickness of the stem.

(A) Secondary growth is the increase in the girth or diameter of a plant,which occurs due to the activity of the vascular cambium and cork cambium.
Hydrophytes are plants that grow in aquatic environments.
In most hydrophytes,the vascular cambium is either absent or poorly developed because they do not require significant structural support or water transport capacity compared to terrestrial plants.
Therefore,secondary growth is typically absent in hydrophytes.

(B) The cork cells (phellem) are dead and compactly arranged without intercellular spaces. Their cell walls are thickened with the deposition of suberin,a fatty substance,which makes them impermeable to water. This prevents water loss from the plant body.

(A) The extrastelar secondary growth involves the formation of tissues outside the stele,specifically in the cortex region.
This process is initiated by the formation of the cork cambium,also known as $Phellogen$.
$Phellogen$ cuts off cells on both sides: the cells produced towards the outside become $Phellem$ (cork),and the cells produced towards the inside become $Phelloderm$ (secondary cortex).
Together,$Phellem$,$Phellogen$,and $Phelloderm$ are known as the $Periderm$.

(A) The periderm is a collective term for the protective tissues formed during secondary growth in plants. It consists of three layers:
$1$. Phellogen (cork cambium),
$2$. Phellem (cork),and
$3$. Phelloderm (secondary cortex).
Since the phellogen is a type of cambium,and the cork is included,the most appropriate answer among the given choices is $A$ (Cork),as it is a primary component of the periderm. However,if the question implies components of the periderm,it specifically includes phellogen,phellem,and phelloderm.

(A) During secondary growth,the centrally located xylem becomes non-functional due to the deposition of organic compounds like tannins,resins,and oils. This central,non-functional region is known as heartwood or duramen. The outer,younger rings of secondary xylem,which remain functional and are responsible for the conduction of water and dissolved minerals from the roots to the leaves,are called sapwood or alburnum.

(B) The term $Bark$ is a non-technical term that refers to all tissues exterior to the vascular cambium.
It includes the secondary phloem,the periderm (which consists of the phellogen or cork cambium,phellem or cork,and phelloderm or secondary cortex).
Therefore,the bark encompasses all tissues located outside the vascular cambium.

(B) Secondary xylem is commonly referred to as wood. It is formed during the secondary growth of plants by the vascular cambium. It consists of tracheids,vessels,xylem fibres (wood fibres),and xylem parenchyma,which provide structural support and facilitate water transport.

(B) The age of a tree can be determined by counting the number of annual rings present in the trunk.
In temperate regions,the cambium is active during the spring and less active during the autumn,leading to the formation of distinct light and dark rings known as annual rings.
Each pair of one light ring (spring wood) and one dark ring (autumn wood) represents one year of growth.
This method is known as dendrochronology.

(D) Lenticels are small,lens-shaped openings or pores found in the periderm of woody stems and roots.
These structures consist of loosely arranged parenchyma cells that allow for the exchange of gases between the internal tissues of the plant and the external atmosphere.
Since the periderm is generally impermeable to gases and stomata are absent in these woody organs,lenticels serve as the primary site for gaseous exchange and limited transpiration.

(B) Growth rings,also known as annual rings,are formed in the secondary xylem of woody plants due to the seasonal activity of the vascular cambium.
The vascular cambium is located within the stele of the stem and is therefore referred to as the intrastelar cambium.
During spring,the cambium is very active and produces large-sized xylem elements with wide vessels,forming early wood (spring wood).
During autumn or winter,the cambium becomes less active and produces narrow,thick-walled xylem elements,forming late wood (autumn wood).
The alternation of these two types of wood in a single year creates a distinct growth ring.

(D) The procambium is a primary meristematic tissue that gives rise to the primary vascular tissues.
It differentiates into primary xylem,primary phloem,and the intrafascicular cambium.
The interfascicular cambium,however,is formed by the dedifferentiation of the parenchyma cells of the medullary rays (interfascicular parenchyma) during secondary growth.
Therefore,the interfascicular cambium is not derived from the procambium.

(D) Ring porous wood is characterized by the presence of large vessels formed early in the season (early wood) to meet the high transpiration demand of developing leaves.
Diffuse porous wood has vessels of more or less uniform size distributed throughout the growth ring,allowing for a steady and consistent supply of water throughout the growing season.
Therefore,statement $D$ is correct because ring porous vessels are specifically adapted to conduct large volumes of water during the early part of the season when the metabolic and transpirational needs of the plant are highest.

(C) Annual rings are formed due to the differential activity of the cambium,which is influenced by seasonal climatic variations.
In coastal or sea-shore areas,the climate remains relatively constant throughout the year due to the moderating effect of the sea,creating isothermal conditions.
Since there is no significant seasonal fluctuation in temperature or environmental conditions,the cambium remains active throughout the year,preventing the formation of distinct annual rings.

(C) During secondary growth in a dicot root,the process begins with the cells of the conjunctive tissue located just below the phloem bundles becoming meristematic.
These parenchymatous cells undergo division to form a strip of cambium.
Subsequently,the pericycle cells located outside the protoxylem also become meristematic.
These strips join together to form a complete,wavy ring of vascular cambium,which later becomes circular and starts cutting off secondary xylem towards the inside and secondary phloem towards the outside,leading to an increase in the girth of the root.

(C) The age of a tree is determined by counting the annual rings present in the oldest part of the trunk,which is at the base.
Since the tree is $100$ years old,the base will show approximately $100$ annual rings.
As we move towards the apex (top) of the tree,the stem represents younger growth,meaning fewer annual rings are formed in the upper branches compared to the base.
Therefore,the number of annual rings decreases uniformly from the base towards the apex.

(A) The nail will remain at $1$ meter above the soil level.
This is because the growth in height of a tree occurs primarily due to the activity of the apical meristems located at the tips of the shoots.
The trunk of the tree increases in girth due to secondary growth (lateral meristems),but the vertical position of any point on the mature trunk remains fixed relative to the ground as the tree grows taller from the top.

(B) The correct answer is $(B)$.
In temperate regions,the cambium is active for a specific period of the year,leading to the formation of annual rings.
Each annual ring consists of one ring of spring wood and one ring of autumn wood,representing one year of growth.
By counting these annual rings,the age of the tree can be accurately determined.
The scientific method of determining the age of a tree by counting its annual rings is known as Dendrochronology.

(D) Grafting is a horticultural technique where tissues from one plant are inserted into those of another so that the two sets of vascular tissues may join together.
This process requires the presence of $cambium$ (meristematic tissue) in both the stock and the scion to facilitate secondary growth and vascular connection.
Since monocots lack $cambium$ in their vascular bundles,they cannot undergo secondary growth,making it impossible for the tissues of two different plants to fuse and form a functional connection.
Therefore,the correct option is $(d)$.

(C) In mature woody stems,the epidermis is replaced by a protective layer called the periderm,which includes the cork (phellem).
Lenticels are small,lens-shaped openings or pores found on the surface of woody stems.
These structures allow for the exchange of gases between the internal tissues of the stem and the outer atmosphere.
They appear as scars on the bark because they are areas where the cork cells are loosely arranged,allowing for gas diffusion.

(B) Cork cells,also known as phellem,are formed by the activity of the cork cambium (phellogen).
As these cells mature,their cell walls become thickened due to the deposition of a waxy,hydrophobic substance called suberin.
Suberin makes the cork cells impermeable to water and gases,which helps in protection and preventing water loss from the plant body.

(B) In woody stems and old trees,the bark is covered with cork,which is impermeable to gases.
To facilitate gas exchange,small pores called lenticels are present on the bark.
These lenticels allow for the diffusion of $O_2$ and $CO_2$ between the internal tissues and the atmosphere.
Therefore,old trees obtain $O_2$ primarily through lenticels.