Short questions:

1.How does the xylem differ from the phloem?

Ans:The xylem differ from the phloem by the following ways;

1.Xylem: It is a complex tissues that is mainly responsible for the conduction of water and saps inside the plant from the root upto the top of the plant. It also provides mechanical strength. Xylem is commonly known as wood which is composed of 4 kinds of cells respectively, tracheids, vessels, wood parenchyma and wood fibres.

2.Phloem: It is living, non lignified tissue also called bast. Its main function is to transport organic food inside the plant body from the leaves to the storage organ and from the storage organ to various parts according to the need of the organ. It consists of sieve tubes, companion cells, phloem parenchyma, bast fibres.

 

2.What do you know about the apical meristem?

Ans:The meristems loacated at the apices or the growing points of main and lateral shoots and roots are called apical meristems. They include both promeristems and primary meristems.

 

3.Describe the nature of secretory cells in plants.

Ans:In plants, secretory cells concerned with the secretion of gums, resins, oils, latex, nector, etc. The secretion may be useful or may not be useful to the plant.

 

4.Give the anatomical differences between the dicot root and stem.

Ans:

 

5.Which features help you to identify whether the given material is a T.S. of the root or stem?

Ans: Following features help to identify whether the given material is a T.S. of the root or stem;

 

 

 

 

Root	Stem
1.Epidermis usually has no cuticle layer and stomata.	1.Epidermis is always covered with a thick or thin layer of cuticle.
2.The epidermis contains unicellular root hairs.	2.If the hair is present, it is multicellular.
3.Cortex is broad and well developed.	3.Cortex is only present in dicot stem and it is narrow.
4.Endodermis is distinct.	4.Endodermis is not distinct.
5.Pericycle is usually single layered.	5.In a dicot stem, pericycle is usually multilayerd.
6.The vascular bundles are of radial type.	6.The vascular bundles are conjoint and collateral type.
7.Exarch xylem is the characteristic features of the root.	7.Endarch xylem is the characteristics features of the stem.

 

 

6.Explain the structure of the vascular bundle in the dicot stem.

Ans: The structure of the vascular bundle in the dicot stem are given below;

Vascular bundle are arranged in a ring around the central pith and inner to pericycle. These are conjoint, collateral, open and wedge- shaped. Each bundle contain patch of xylem towards centre and phloem towards periphery and a strip of cambium in between them. There lies a layer of meristematic cell between the xylem and the phloem which is known as the cambium.

 

7.Draw a sketch of a single vascular bundle of a monocot stem and label it.

Ans:

                                Fig. Monocot stem

 

8.Discuss the nature of the vascular bundle in a monocot root.

Ans: The vascular bundles in a monocot root are of radial type. Xylem and phloem are found at different radii alternating with the each other. The xylem and phloem bundles are numerous. The xylem shows exarch conditions. Phloem consists of sieve- tubes, companion cells and phloem parenchyma. The phloem fibres are absent.

 

9.Give any four points of anatomical difference between a monocot stem and a dicot stem.

Ans: The four anatomical difference between a monocot stem and a dicot stem are given below:

 

 

Dicot stem	Monocot stem
1.Epidermis usually contains multicellular hairs.	1.Epidermis is usually without hairs.
2.Hypodermis is collenchymatous.	2.Hypodermis is usually sclerenchymatous.
3.The vascular bundles are wedge-shaped.	3.Vascular bundles are oval or rounded.
4.Secondary growth occurs due to the presence of cambium.	4.Secondary growth is usually absent.

 

 

10.Distinguish between the following:

a. Meristematc tissue and permanent tissue.

Meristematic tissues:

1. These tissues have the capacity to divide.

2. They have thin cellulose wall.

3. They do not have intercellular spaces.

4. They contain dense cytoplasm with prominent nucleus.

Permanent tissues:

1. These tissues have lost the capacity of division.

2. They have thick cellulose wall.

3. They have large intercellular spaces.

4. They contain thin cytoplasm with normal nucleus.

 

b.Vascular cambium and cork cambium

Vascular Cambium:

1. The Vascular cambium is the remnant part of the apical meristem. It is present between the xylem and phloem of Vascular bundle.

2. This cambium continues to divide and adds secondary phloem on its outer side surrounded secondary xylem on its innerside.

3. The vascular cambium produces primary xylem and medullary rays respectively.

Cork Cambium:

1. The cork cambium is a true secondary meristem which develops in the region outside the vascular tissues.

2. This cambium gives rise to cork and secondary cortex towards outer and inner sides respectively.

3. The cork cambium produces phellogen, phellem and phelloderm collectively known as periderm.

 

c.Exarch xylem and endarch xylem.

Exarch xylem :

1.It in which the metaxylem is towards the centre.

2.It in which the protoxylem is towards the periphery.

Endarch xylem:

1.It in which the  metaxylem is towards the periphery.

2.It is which the protoxylem is towards the centre.

 

d.Conjoint vascular bundles and radial vascular bundles.

Conjoint vascular bundles:

1.The bundles which contain both xylem and phloem on same radii are called conjoint vascular bundle.

2.It is of 2 types; collateral and bicollateral.

 

Radial vascular bundles:

1.Xylem and phloem are seen as  patches and they alternate each other, and occupy the different radii on the same axis separated by non conductive tissues.

2. Examples; dicot and monocot root.

 

e.Seive tubes and sieve cells.

Sieve Cells

1. Found in gymnosperms and pteridophytes.

2. Not associated with companion cells.

3. Sieve areas without sieve plates.

4. Long, elongated cells with tapering end walls.

Sieve Tubes

1. Found in angiosperms.

2. Associated with companion cells.

3. Sieve areas with sieve plates.

4. Shorter but wider cells placed one above the other and connected at the end walls by sieve pores.

 

f.Latex vessels and latex cells.

Latex cells

1. They are known as non-articulated latex ducts.

2. They are independent units and simple cells.

3. These originate as minute structure, quickly elongate and ramify by repeated branching.

Latex vessels

1. They are brown as articulated latex ducts.

2. They are formed by the fusion of several cells.

These originate in meristems from rows of cells and grow parallel.

g.Heart wood and sap wood.

Heartwood:

1. Heartwood is produced after of a few years of secondary growth.

2. Most of the heartwood nears the center of the axis forms a dark coloured region is called heartwood or duramen.

3. Heartwood is formed due to accumulation of organis compounds, such as oils gums, and resins, etc.

4. The Heartwood is dark coloured and non-functional. The major function of this wood is mechanical support.

5. Amount of heartwood increases as the tree grows older.

Sapwood:

1. This is also produced due to secondary growth.

2. There is a small outer region, however, remains light coloured is known as sapwood or alburamen.

3. Sapwood is lighter coloured and it is the outer region of the secondary xylem. It is formed due to the cambial activity of the secondary xylem.

4. The cells of the sapwood are functionally active. So it helps in conduction of water.

5. The amount of sapwood, however, remains almost constant.

 

h.Periderm and bark

The periderm is the outer bark of a tree.The periderm is a secondary tissue that replaces epidermis in roots and stems, and which consists of phellem, phellogen, and phelloderm (it includes dead tissues). while the inner bark is called the phloem,It conducts usable food from the leaves to the cambium to nourish it or to storage areas in the wood (it includes living tissues)and consists of of alternating wedges of sieve tube tissue and radial parenchyma, most of the former crushed by secondary growth.

 

i.Medullary ray and vascular ray.

Medullary ray:

1.Xylem fibers create a radial sheet of tissue known as medullary ray.

2.The medullary rays transport substances from the xylem and phloem to the inner and outer parts of the stem.

 

Vascular ray:

1.The ray initials are isodiametric cells—about equal in all dimensions—and they produce the vascular rays, which constitute the horizontal system of secondary tissues.

2.This horizontal system acts in the translocation and storage of food and water.

 

j.Autumn wood and spring wood.

Early wood or Spring wood

1. Formed during spring season.

2. Formed early in a year.

3. Consists of xylem tissues with wider vessels.

4. Produced more in amount.

5. Less dense.

6. A broad zone of wood.

7. Not as strong as late wood.

Late wood or Autumn wood

1. Formed during winter season.

2. Formed after the early wood.

3. Consists of xylem elements with narrow vessels.

4. Produced less in amount.

5. More dense.

6. A narrow zone of wood.

7. Stronger than early wood due to larger volume of wall materials.

 

k.Primary xylem and secondary xylem

Primary Xylem:

1. It is primary in nature and is derived from procambium.

2. It is differentiated into protoxylem and metaxylem.

3. Tracheids and vessels are narrow and long vessels do not possess tylosis.

4. Xylem fibres are less in number.

5. No differentiation of sapwood and heartwood and no formation of annual ring.

Secondary Xylem:

1. It is secondary in nature and is derived from fascicular and interfascicular cambium.

2. No such differentiation is seen.

3. These are wide and short. Vessels are blocked by tyloses.

4. These are abundantly present.

5. Sapwood and heartwood are distinct annual ring formation occurs.

 

l.Primary phloem and secondary phloem.

Primary phloem

1. Derived from procambium of apical meristem.

2. District protophloem and metaphloem elements.

3. Sieve tubes long and narrow.

4. Less or no development of phloem parenchyma.

5. Phloem fibres on the outer part.

Secondary phloem

1. Derived from vascular cambium.

2. No clear demarcation between protophloems and metaphloems.

3. Sieve tubes short and wide.

4. Well developed and abundant phloem parenchyma.

5. Phloem fibers among the phloem parenchyma.

 

11.Write notes on:

1.Parenchyma:

It is most common permanent tissues. They are thin walled living cells which are oval, spherical or polygonal in shape. They contain large vacuole. The cells have intercellular spaces in between them which may small or big. This tissue is generally present in almost all the organs. They are of following types;

a.Prosenchyma: In some cases the parenchymatous cell become long and taper at either end such tissues is called prosenchyma.

b.Aerenchyma: Some cells have wide air spaces between them called aerenchyma.

c.Chlorenchyma: In the leaves, the palisade cells are long and contain chloroplast in them. They help in photosynthesis and are essentially parenchyamatous due to their contain chlorophyll.

Functions of parenchyma:

1.Parenchymatous cells help in photosynthesis. e.g palisade cells of leaf.

2.It servers mainly for the storage of food materials in the form starches, proteins, oils and fats.

 

2.Collenchyma:

Collenchyma are the living cells which are somewhat elongated. Cells of this tissues possess localized thickening on the cell wall, particularly at the corner. It occurs in the herbaceous dicotyledons e.g. sunflower, gourd, etc.

Functions:

1.It gives mechanical strength to the organs.

2.It also manufacture sugar and starch.

3.In some plants, collenchyma cell regain the power to divide.

 

 3.Sclerenchyma:

It consists of long, narrow, thick walled and lignified cells which are dead cells and do not perform any metabolic activities. They are found abundantly in plants and occurs in patches or in definite layers.

Functions:

1.They give strength and rigidity to plant body.

2.They also enable it to withstand mechanical strength.

Sclerenchyma are of two types;

1.Fibres

2. Sclereids

4. Periderm:

The periderm is the secondary protective (dermal) tissue that replaces the epidermis during growth in thickness of stems and roots of gymnosperms and dicotyledons (i.e., secondary growth). Unlike typical epidermis, the periderm is a multilayered tissue system, the bulk of which usually constitutes the cork, or phellem. Phellem (the cork) consists of cells that are dead at maturity, and their primary walls become covered from the inside by the secondary wall which consists of parallel suberin lamellae alternating with wax layers. The lateral meristem, (cork cambium or phellogen), is one cell layer thick and encircles the stem. 

 

5.Lenticels:

 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. It functions as a pore, providing a pathway for the direct exchange of gases between the internal tissues and atmosphere through the bark, which is otherwise impermeable to gases. Lenticels are found as raised circular, oval, or elongated areas on stems and roots. As stems and roots mature lenticel development continues in the new periderm (for example, periderm that forms at the bottom of cracks in the bark). Lenticels are also found in pneumatophorous roots (respiratory roots).

6.Annual rings:

Annual rings, the growth layers of wood that are produced each year in the stems and roots of trees and shrubs. In climates with well-marked alternations of seasons (either cold and warm or wet and dry), the wood cells produced when water is easily available and growth is rapid (generally corresponding to the spring or wet season) are often noticeably larger and have thinner walls than those produced later in the season when the supply of water has diminished and growth is slower. There is thus a sharp contrast between the small, thick-walled late-season wood cells produced one year, and the large, thin-walled cells of the spring wood of the following year results. Where the climate is uniform and growth continuous, as in wet, tropical forests, there is usually little or no gross visible contrast between the annual rings, although differences exist. When rings are conspicuous, they may be counted in order to obtain a reasonably accurate approximation of the age of the tree. They are also reflective (by their range of thickness) of the climatic and environmental factors that influence growth rates. The science of dendrochronology is based upon the phenomenon of variability in the thickness of annual rings.

7.Tyloses

Tylosis  is the physiological process and the resulting occlusion in the xylem of woody plants as response to injury or as protection from decay in heartwood. Tyloses are outgrowths on parenchyma cells of xylem vessels (vascular tissue used for water and mineral transport throughout a plant). When the plant is stressed by drought or infection, tyloses will fall from the sides of the cells and "dam" up the vascular tissue to prevent further damage to the plant. Tyloses can aid in the process of making sapwood into heartwood in some hardwood trees, especially in trees with larger vessels.These blockages can be used in addition to gum plugs as soon as vessels become filled with air bubbles, and they help to form a stronger heartwood by slowing the progress of rot.

 

 

Long Questions:

1.What are meristems? Discuss their role in plants?

Ans: It can be defined as a group of immature cells which has the capacity of division. They are living cells, small and thin walled.

Apical meristems are the completely undifferentiated (indeterminate) meristems in a plant. These differentiate into three kinds of primary meristems. The primary meristems in turn produce the two secondary meristem types. These secondary meristems are also known as lateral meristems because they are involved in lateral growth. 

At the meristem summit there is a small group of slowly dividing cells which is commonly called the central zone. Cells of this zone have a stem cell function and are essential for meristem maintenance. The proliferation and growth rates at the meristem summit usually differ considerably from those at the periphery. 

The apical meristem, or growing tip, is a completely undifferentiated meristematic tissue found in the buds and growing tips of roots in plants. Its main function is to begin growth of new cells in young seedlings at the tips of roots and shoots (forming buds, among other things). Specifically, an active apical meristem lays down a growing root or shoot behind itself, pushing itself forward. Apical meristems are very small, compared to the cylinder-shaped lateral meristems . 

Apical meristems are composed of several layers. The number of layers varies according to plant type. In general the outermost layer is called the tunica while the innermost layers are the corpus. In monocots, the tunica determine the physical characteristics of the leaf edge and margin. In dicots, layer two of the corpus determine the characteristics of the edge of the leaf. The corpus and tunica play a critical part of the plant physical appearance as all plant cells are formed from the meristems. Apical meristems are found in two locations: the root and the stem. Some arctic plants have a apical meristem in the lower/middle parts of the plant. It is thought that this kind of meristem evolved because it is advantageous in arctic conditions. 

 

 

2.What are permanent tissues? Mention the structure and function of the simple permanent plant tissue.

Ans: A permanent tissues is a group of cells that have lost the powe of cell division and the growth. The permanent tissues can be classified into two types:

A.Simple permanent tissue:

These tissues are the group of cells which are similar in origin, form and  function. These are also mainly three types;

1.Parenchyma:

 It is most common permanent tissues. They are thin walled living cells which are oval, spherical or polygonal in shape. They contain large vacuole. The cells have intercellular spaces in between them which may small or big. This tissue is generally present in almost all the organs. They are of following types;

a.Prosenchyma: In some cases the parenchymatous cell become long and taper at either end such tissues is called prosenchyma.

b.Aerenchyma: Some cells have wide air spaces between them called aerenchyma.

c.Chlorenchyma: In the leaves, the palisade cells are long and contain chloroplast in them. They help in photosynthesis and are essentially parenchyamatous due to their contain chlorophyll.

Functions of parenchyma:

1.Parenchymatous cells help in photosynthesis. e.g palisade cells of leaf.

2.It servers mainly for the storage of food materials in the form starches, proteins, oils and fats.

3.In the fleshy stems of leaves, it helps in store water.

B.Collenchyma:

 

Collenchyma are the living cells which are somewhat elongated. Cells of this tissues possess localized thickening on the cell wall, particularly at the corner. It occurs in the herbaceous dicotyledons e.g. sunflower, gourd, etc.

Functions:

1.It gives mechanical strength to the organs.

2.It also manufacture sugar and starch.

3.In some plants, collenchyma cell regain the power to divide.

C.Sclerenchyma:

It consists of long, narrow, thick walled and lignified cells which are dead cells and do not perform any metabolic activities. They are found abundantly in plants and occurs in patches or in definite layers.

Functions:

1.They give strength and rigidity to plant body.

2.They also enable it to withstand mechanical strength.

Sclerenchyma are of two types;

1.Fibres: Fibres are long and tapering at ends which are thick walled cells. The fully developed fibres are always dead. They are present in the xylem of stems and roots, testa of various seeds. Its main function is to give mechanical strength.

2.Sclereids: They are extremely thick walled and may be spherical, oval, cylindrical, etc. They are generally found in hard parts of plant body sometimes in the pulp of fruits. They are be classified into four main types on the basis of their shapes. Its main function is to provide local mechanical strength.

 

3.Describe various components of xylem and phloem.

Ans: The various components of xylem and phloem are given below;

1.Xylem:

 It is a complex tissues that is mainly responsible for the conduction of water and saps inside the plant from the root upto the top of the plant. It also provides mechanical strength. Xylem is commonly known as wood which is composed of 4 kinds of cells respectively, tracheids, vessels, wood parenchyma and wood fibres.

Xylem are of two types they are protoxylem and metaxylem.

 

Protoxylem:

It is early formed xylem which bears narrow vessels. It is retained only for a short period where fibres are absent or rare.

Metaxylem:

 It is late formed xylem which bears large vessels. It is retain for long period where fibres often occurs.

2.Phloem:

 It is living, non lignified tissue also called bast. Its main function is to transport organic food inside the plant body from the leaves to the storage organ and from the storage organ to various parts according to the need of the organ. It consists of sieve tubes, companion cells, phloem parenchyma, bast fibres. Phloem are of two types primary and secondary phloem.

Primary phloem:

It is develop from procambium which is differentiated into protophloem and metaphloem.

Secondary phloem:

It is developed from cambium during secondary growth which shows radial differentiation.

 

 

4.Draw a labeled sketch of the T.S. of a young dicot stem and explain the nature  of the vascular bundle.

Ans: The internal structure of a dicot stem can be studied from transverse section of a young sunflower.

1.Epidermis:

It is the outermost layer and consists of a single layer of parenchymatous cells. The outer walls are greatly thickened and heavily cutinized. It protects the underlying tissues from mechanical injury and prevents the entry of harmful organisms.

 

 

2.Hypodermis:

This layer is below the epidermis and is composed of 4 or 5 layers of collenchymatous cells. The cells are living and may contain few chloroplasts. It provides mechanical strength and elasticity to the peripheral portion of the stem. It also acts as storage of food.

3.General cortex:

It lies internal to the hypodermis and consists of a few layers of thin walled, large, rounded, oval, living parenchymatous cells , having conspicuous intercellular spaces. They serve for storage of food.

4. Endodermis:

 It is the innermost layer of the cortex and separates the cortex from stele. They are barrel shaped and compactly arranged having no intercellular spaces. They serve as food reserve.

5.Stele:

 Part of stem inside of cortex is known as the stele. It consists of four regions they are the pericycle, the vascular bundle region, pith and the medullary rays.

6.Pericycle:

The region between the vascular bundles and the cortex is known as thye pericycle. Parenchymatous pericycle is present outside the medullary rays which serves to store food.

7.Vascular bundle:

 These are arranged in a ring around the central pith and inner to pericycle. These are conjoint, collateral, open and wedge- shaped. Each bundle contain patch of xylem towards centre and phloem towards periphery and a strip of cambium in between them. There lies a layer of meristematic cell between the xylem and the phloem which is known as the cambium.

8.Pith:

The centre of the stem is pith or medulla which is composed of parenchymatous cell. Food is stored in this region.

Nature of vascular bundles:

Vascular bundles are a strand of conducting tissue which consist of xylem and phloem. On the basis of arrangement of xylem and phloem, they are of Radial, conjoint and amphivasal.

Function of vascular bundles are;

1.They are responsible for transport of  food, minerals and water within the plant.

2.They provide mechanical support to the plants.

 

 

5.Discuss the structure of dicot root. Point out the nature of its vascular bundle.

 

 

 

     

Ans:The internal structure of a dicot root can be studied from transverse section of a young root of sunflower, gram and pea. It shows the following arrangement of tissues from the periphery to the centre.

1.Epiblema or piliferous layer:

 Ebliblema is the outermost single layer. It is composed of thin- walled, closely packed parenchymatous cells without intercellular spaces. Unicellular root hairs are present in epiblema.

2.Cortex:

It lies below the epiblema and consists of many layers of thin walled rounded or polygonal parenchymatous cells. Cotex cells store food and conduct water from epiblema to the inner tissues.

3.Endodermis:

It is the innermost layer, made up of a single layer of barrel shaped compact parenchyamatous cells without intercellular spaces. Cells of endodermis lying opposite the protoxylem elements are thin walled and known as passage cells because they allow the passage of water from roots to the xylem.

3.Pericycle:

 It lies internal to the endodermis and composed of single layer of thin walled parenchymatous cells containing abundant protoplasm.

5.Conjunctive tissue:

 The parenchyma lying in between xylem and phloem bundles constitutes the conjunctive tissue.

6.Vasculare bundles:

These are arranged in an ring but xylem and phloem form an equal number of separate bundles placed on different radii.

7.Pith: It occupies small area in the centre and consists of a few compactly arranged, thin- walled parenchymatous cells without any intercellular space.

The nature of its vascular bundle are given below;

These are arranged in an ring but xylem and phloem form an equal number of separate bundles placed on different radii.

a.Xylem: It appears conical in shape and are thick walled. Protoxylem lies towards the periphery, so the xylem is exarch while metaxlyem vessels meet in the centre and pith gets obliterated. Xylem parenchyma and fibres are absent and a few tracheids are present around the vessels.

b.Phloem: It lies alternate to xylem patches. The patches are smaller and consists of sieve tubes, companion cells and phloem parenchyma. The phloem fibres are absent. The outerpart of this tissue next to pericycle is the protophloem and inner is the metaphloem.

 

 

6.What is the secondary growth? Describe the process of the secondary growth in a dicot stem.

Ans: The secondary growth may be defined as an increase in thickness due to the formation of secondary tissues cut off by the cambium and cork cambium in the stellar and extrastelar regions.

The secondary growth in dicot stem occurs due to activity of cambium at stellar region and activity of cork cambium at extrastelar region. Stelar secondary growth leads to formation of annual ring.

 

In dicot stem, secondary growth takes place through the following steps:

 

Origin and activity of cambium- Generally, dicot stem contains disjoint, collateral, open and endarch vascular bundles arranged in a ring. The fascicular cambium is present between xylem and phloem of each vascular bundle.

At the time of secondary growth, the parenchymatous cells of primary meduallary rays lying between the edges of fascicular cambium become meristamic. They divide, redivide, and form a strip interfascicular cambium. The interfascicular cambium joins with fascicular cambium of either side and forms a complete ring of cambium. Secondly, growth begins with the activity of this cambium ring. Cambium cuts down secondary phloem towards the periphery and secondary xylem towards the center. Normally, cambium produces more secondary xylem than secondary phloem. Due to formation of more secondary tissues, the primary tissues are pushed apart from each other and remain small patches or the completely crushed.

The secondary xylem consists of vessels, tracheids, wood fibres and wood paremchyma. Vessels are more abundant. The secondary phloem consists of sieve tubes, companion cells, phloem parenchyma and phloem fibres or bast fibres. The cells of secondary phloem are arranged in radial rows. The cambial cells between vascular bundles cut down secondary phloem.

Annual ring formation- the activity of cambium is influenced by the variations of climate. It produces more vessels with inner cavity during spring called the spring wood and less vessels with narrow cavities, more tracheids and wood fibres in autumn called autumn wood or late wood. These two types together form a growth ring or annual ring. By counting the total number of annual ring, the approximate age of the plant can be determined. After a long period of secondary growth, two types of woods appear in the stem such as, sapwood, heartwood. Sapwood is recently formed wood and heartwood is earlier formed wood.

 

 

7.Discuss the anatomical structure of the monocot stem. Point out its peculiarities.

                                  Fig; Structure of monocot stem

 

The internal structure of a monocot stem ( maize) can be studied as following internal structure;

1.Epidermis: It is single outermost layered which is composed of small thin walled parenchymatous cells. A few stomata are present in the epidermis.

2.Cortex: It is not well differentiated into distinct region but is composed of hypodermis and ground tissues regions. Hypodermis lies just below the epidermis and ground tissue lies below the hypodermis. Vascular bundles are irregularly embedded in this region.

3.Vascular bundles: They are conjoint, collateral , closed and irregulary scattered in the ground tissue. It consists of xylem and phloem.In this type xylem is Y-shaped bearing two large metaxylem and phloem lies outside the xylem which is composed of sieve elements and companion cells.

Diagnostic Features of a Monocot Stem:

 1.Absence of trichomes.

2.Presence of stomata.

3.Presence of a hypodermis made up of sclerenchyma.

4.Presence of undifferentiated ground tissue.

5.Presence of numerous vascular bundles irregularly scattered with cerifugal arrangement.

6.Vascular bundles are conjoint, collateral & closed with endarch xylem.

7.Presence of only two protoxylem & two metaxylem vessels in each bundle.

 8.Presence of a lysigenous cavity.

9.Absence of phloem parenchyma.

10.Presence of a bundle sheath made up of sclerenchyma.

 

 

8.Draw a labeled sketch of the monocot root and point out the difference with that of the dicot root.

Ans:

                

                    Fig. Anatomical structure of monocot root

The internal structure of a monocot root (maize) can be described as follows;

1.Epidermis: The epidermis or outermost layer of the root is known as rhizodermis which is uniseriate and composed compact cells having no inter cellular spaces. Epidermis hairs absorb water and minerals salt.

2.Cortex: The epidermis or massive cortex lies consisting of thin walled parenchyma cell having intercellular spaces. It help in conduction of water and minerals salts from root hairs to inner tissues and storage of food.

3.Endodermis: It is innermost layer of cortex which is composed of barrel shaped, compact cells having no intercellular spaces. Young endodermal cell have internal strip of suberin and lignin. Endodermis is to regulate flow of fluid both inward as well as outward.

4.Stele: It consists of pericycle and vascular tissues where pericycle lies just below the endodermis and is composed single layered sclerenchymatous cells and in other side vascular tissues consists of alternating strands of xylem and phloem. The bundles are numerous and referred as polyarch.

The difference between monocot root and dicot root are given below:

Dicot root	Monocot root
1.Cortex is not differentiated into exodermis or hypodermis.	1.Cortex is usually differentiated into outer exodermis or hypodermis.
2.Pericycle gives rise to lateral roots and cambium at the time of secondary growth.	2.Pericycle gives lateral roots only.
3.The number of xylem and phloem bundles are usually two to six, rarely eight.	3.The number of xylem and phloem bundles are usually 8 to 20 and sometimes reach up to 100 or more.
4.Pith is either absent or highly reduced.	4.Well developed pith is present.
5.Secondary growth is present.	5.Secondary growth is absent.