TS Inter 1st Year Botany Study Material Chapter 12 Histology and Anatomy of Flowering Plants

Telangana TSBIE TS Inter 1st Year Botany Study Material 12th Lesson Histology and Anatomy of Flowering Plants Textbook Questions and Answers.

TS Inter 1st Year Botany Study Material 12th Lesson Histology and Anatomy of Flowering Plants

Very Short Answer Type Questions

Question 1.
The transverse section of a plant material shows the following anatomical features –
a) the vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheaths.
b) phloem parenchyma is absent. What will you identify it as?
Answer:
Monocotyledonous stem with closed vascular bundles.

Question 2.
Why are xylem and phloem called complex tissues?
Answer:

1. Complex tissues is made of more than one type of cells that work together as a unit.
2. Xylem and phloem are made of more than one type of cells i.e., parenchyma, fibers etc.

Question 3.
How is the study of plant anatomy useful to us?
Answer:

1. Anatomy is useful to known the internal structure of the plant. It is useful in classification of plants based on natural relations.
2. It is useful to understand the plant functions, habitat of the plant and evolution of plants.

Question 4.
Protoxylem is the first formed xylem. If the protoxylem lies radially next to phloem, what kind of arrangement of xylem would you call it? Where do you find it?
Answer:

1. Radial arrangement
2. They are found in roots.

Question 5.
What is the function of phloem parenchyma?
Answer:
Phloem parenchyma stores food materials and other substances like resins, latex and mucilage.

Question 6.
a) What is present on the surface of the leaves which helps the plant to prevent loss of water but is absent in roots?
b) What is the epidermal cell modification in plants which prevents water loss?
Answer:
a) Cuticle
b) Bulliform cells is Isobilateral (monocotyledonous) leaf.

Question 7.
Which part of the plant would show the following?
a) Radial vascular bundle
b) Polyarch xylem
c) Well developed pith
d) Exarch xylem
Answe:
a) Radid vascular bundle – Root
b) Polyarch xylem – Monocot root
c) Well developed pith – Monocot root
d) Exarch xylem – Root

Question 8.
What are the cells that make the leaves cur! in plants during water stress? Give an example.
Answer:

1. Large, colourless Bulliform ceils
2. Ex : Monocot (Grass) leaves

Question 9.
What constitutes the vascular cambial ring?
Answer:

1. Intrafascicular cambium and interfasicular cambium.
2. Cambial ring is formed in dicot stem during secondary growth.

Question 10.
Give one basic functional difference between phellogen and phelloderm.
Answer:

1. Phellogen (cork cambium) is a meristematic tissue, formed from primary cortex.
2. Phelloderm (secondary cortex) is a permanent tissue formed by inner cells that cuts off from phellogen.

Question 11.
If one debarks a tree, what parts of the plant are removed?
Answer:

1. Periderm and secondary phloem are removed.
2. All those tissues exterior to the vascular cambium.

Short Answer Type Questions

Question 1.
State the location and function of different types of Meristems. [Mar. ’20, ’17, ’15, ’13]
Answer:
Based on location. Meristems are three types.

1. Apical meristems :
They are present at the growing tips of roots, stem,, branches etc., They help in the linear growth of the plant body. These are primary meristems because they appear early in life and contribute to the formation of primary plant body.

2. Intercalary meristem :
They are found in between permanent tissues. This meristem is separated from the apical meristems during the course of plant growth. They help in linear growth of the stem and leaves. Growth of flowers and fruits after their initiation at the apex also occurs due to this meristems. They are active only for a short period. These are also primary meristems.
Eg : Meristems seen at the base of internodes and leaf bases of monocotyledons (particularly grasses).

3. Lateral meristems :
They are found at the lateral sides of the plant body. The cells divide periclinally and increase the thickness of the organs like stem and root. These are secondary meristems.
Eg : Vascular cambium that help in secondary growth by producing secondary xylem and secondary phloem; phellogen (cork cambium) that helps in the formation of periderm.

Question 2.
Cut a transverse section of young stem of a plant from your garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem ? Give reasons.
Answer:

Dicot Stem	Monocot Stem
1. In Epidermis, multicellular hairs trichomes are present.	1. Trichomes are absent.
2. Hypodermis is collenchymatous.	2. Hypodermis is sclerenchymatous.
3. Endodermis, pericycle, medulla medullary rays are present.	3. Endodermis, pericycle, medulla, medullary rays are absent.
4. Vascular bundles are few in number and arranged as a circular ring (eustele).	4. Vascular bundles are numerous and arranged in a scattered manner (atactostele).
5. Vascular bundle is top shaped or wedge shaped.	5. Vascular bundle is oval in shape.
6. Vascular bundle is not enclosed by a bundle sheath.	6. Vascular bundle is enclosed by fibrous sheath, (fibrovascular bundle)
7. Open vascular bundle.	7. Closed vascular bundle.
8. Xylem vessels are more in number.	8. Xylem vessels are few in number.
9. Protoxylem lacunae are absent.	9. Protoxylem lacunae are present.
10. Vessels are in serial order.	10. Vessels are in Y shape.
11. Phloem parenchyma is present.	11. Phloem parenchyma is absent.

Question 3.
What is periderm? How does periderm formation take place in the dicot stems? [Mar. – 2018]
Answer:
Phellogen, Phellem and Phelloderm are collectively known as periderm.

1. Due to the formation of more secondary vascular tissues a pressure is exerted on the epidermis causing its rupture. So a secondary protective layer (periderm) is formed.
2. Parenchyma cells in middle or inner cortex dedifferentiate into a ring of secondary meristem. This is called cork cambium or phellogen. It cuts off new cells on both sides.
3. Tissue produced on outside is called cork tissue or phellem. Tissue produced inside is called secondary cortex or phelloderm.
4. The phellogen, phellem, and phelloderm together constitute periderm.
   
5. To facilitate gaseous exchange in the cork tissue certain bulged lens shaped structures are formed. They are called lenticels.

Question 4.
A transverse section of the trunk of a tree shows concentric rings which are known as annual rings. How are these rings formed? What is the significance of these rings?
Answer:

1. In temperate and cold regions, the activity of cambium is influenced by seasonal variations.
   
2. In favourable conditions growth will be active. So plants require large amounts of water and minerals. During unfavourable conditions plants are less active.
3. In spring, wood formed shows more number of xylem vessels having wide lumens. This is called spring wood or early wood.
4. During autumn, wood formed shows less number of xylem vessels with narrow lumens. This is called autumn wood or late wood.
5. Spring wood and autumn wood appear alternately in the form of circles in the T.S. of a tree trunk. These are called Growth rings or annual rings.
6. By counting the number of annual rings the age of tree can be estimated approximately.

Question 5.
What is the difference between lenticels and stomata? [Mar. – 2019, ’15, May ’17]
Answer:
Lenticels :
Lens shaped openings in the cork of woody trees are called lenticels. They show closely arranged parenchymatous cells. The lenticels permit the exchange of gases between the outer atmosphere and the internal tissues of the woody organs. There is no opening and closing mechanism.

Stomata :
Stomata are present in the upper epidermis and lower epidermis of leaves. They help in exchange of gases. In dicot leaves, on either side of stomata kidney shaped guard cells are present. In monocot leaves, dumb bell shaped guard cells are present. Guard cell contains chloroplast. They help in opening and closing of stomata. Stomata helps in the gaseous exchange and also promote transpiration.

Question 6.
Write the precise function of
a) Sieve tube
b) Interfasicular cambium
c) Collenchyma
d) Sclerenchyma
Answer:
a) Sieve tube :
The functions of sieve tube are controlled by the nucleus of companion cells. The companion cells help in maintaining the pressure gradient in the seive tubes. It transports food materials from leaves to other parts.

b) Interfasicular cambium :
The cells of medullary cells adjoining the intrafascicular cambium becomes meristematic and forms interfasicular cambium.
Thus a continuous ring of vascular cambium is formed.

c) Collenchyma :
The collenchyma cells which contain chloroplast are green in colour. Photosynthetic in function. Intercellular spaces are absent as the corners are thickened with pectin. So they provide tensile mechanical strength. It helps in movement of young stem, petiole of leaf, pedicel of flower.

d) Sclerenchyma :
They are dead cells. Cell walls are thickened with legnin. Intercellular spaces are absent. So they, give mechanical strength to organs.

Question 7.
The stomatal pore is guarded by two kidney shaped guard cells. Name the epidermal cells surrounding the guard cells. How does a guard cell differ from an epidermal cell? Use a diagram to illustrate your answer.
Answer:

• The epidermal cells surrounding the guard cells are called subsidary cells or accessory cells.
• The stoma is bounded by two kidney shaped guard cells in dicots and dumbbell-shaped guard cells in monocots.
• Unlike that of other epidermal cells, guard cells posses chloroplast.
• The wall of the guard cells towards the stomatal pore is thick, while the outer wall is thin. The stoma, guard cell and subsidiary cells together constitutes stomatal complex.

Question 8.
Point out the differences in the anatomy of leaf of peepal [Ficus religiosa] and maize [Zea mays]. Draw the diagrams and label the differences.
Answer:

Dicot leaf Eg : Peepal	Monocot Leaf Eg : Maize
1. Stomata are more on the lower epidermis.	1. Stomata are in equal numbers on both sides.
2. Bulliform cells are absent.	2. Bulliform cells are present on upper epidermis.
3. Mesophyll is differentiated into palisade and spongy tissues.	3. Mesophyll is undifferentiated.
4. Bundle sheath extensions are generally parenchymatous.	4. Bundle sheath extensions are sclerenchymatous.

Question 9.
Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.
Answer:
Yes, Cork cambium or phellogen is a secondary meristematic tissue. It has the capability to divide. It divides and forms new cells on both sides. The tissue produced outside is called cork tissue or phellem. The tissue produced towards in innerside in secondary cortex or phelloderm.

Question 10.
Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.
Answer:
The three basic tissue systems in the flowering plants are

1. Epidermal tissue sytem
2. The ground or fundamental tissue system
3. The vascular or conducting tissue system.

1. Epidermal tissue system consists of parenchymatous tissue. They are epidermis, stomata and out growths.
2. The ground or fundamental tissue system consists of simple tissues such as parenchyma, collenchyma and sclerenchyma.
3. The vascular or conducting tissue system consists of complex tissues, the phloem and the xylem.

Long Answer Type Questions

Question 1.
Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance?
Answer:
Growth of stem or root in thickness due to the formation of secondary tissues due to the activity of primary and secondary meristems is called secondary growth.

Changes during secondary growth of a dicot stem are divided into two groups. They are
I. Intrastelar secondary growth.
II. Extrastelar secondary growth.

I. Intrastelar secondary growth :
The changes that occur inside the stele are called Intrastelar secondary growth. They are

A) Formation of vascular cambial ring :

1. Indicot stem, vascular bundles are in a circular ring. They are open type with fascicular cambiam.
2. Parenchyma in medullary rays dedifferentiate into secondary meristem connecting fascicular cambiam. These are called interfascicular cambiam.
3. Fascicular and interfascicular cambia fuse to form vascular cambial ring.

B) Activity of vascular cambium :
4. Vascular cambium has 2 types of initials.
a) Fusiform initials :
They give rise to secondary xylem towards centre and secondary phloem to outside.

b) Ray initials :
They produce phloem rays towards outside and xylem rays towards inside.
5. More secondary xylem is formed than secondary phloem.
6. Secondary xylem is called wood and secondary phloem bast.

7. As stem increases in thickness primary phloem and primary xylem are crushed and removed.
8. Secondary xylem has vessels, fibres and xylem perenchyma. Vessels are pitted.
9. Secondary phloem has sieve tubes, companion cells, fibres and phloem parenchyma.
10. Xylem ray and phloem ray are also called vascular rays. They are helpful in lateral conduction and storage.

II. Extrastelar secondary growth :
The changes which occur outside the stele are called Extrastelar secondary growth.

1. Due to the formation of more secondary vascular tissues a pressure is exerted on the epidermis causing its rupture. So a secondary protective layer (periderm) is formed.
2. Parenchyma cells in middle or inner cortex dedifferentiate into a ring of secondary meristem. This is called cork cambium or phellogen. It cuts off new cells on both sides.
   
3. Tissue produced on outside is called cork tissue or phellem. Tissue produced inside is called secondary cortex or phelloderm.
4. The pheilogen, phellem, and phelloderm together constitute periderm.
5. To facilitate gaseous exchange in the cork tissue certain bulged lens shaped structures are formed. They are called lenticels.

Question 2.
Draw illustrations to bring out the anatomical differences between
a) Monocot root and Dioofc mot
b) Monocot stem and Dirot stem
Answer:

Question 3.
What are simple tissues? Describe various types of simple tissues.
Answer:
The tissues which are made of only one type of cells are called simple tissues.

The various types of simple tissues are parenchyma, collenchyma and sclerenchyma.

Parenchyma :

1. The Parenchyma is a living tissue. It occupies a major part of the plant body. So it is known as fundamental tissue or ground tissue.
2. The cells are isodiamtetric. They may be spherical, oval round, polygonal or elongated in shape.
3. Cell walls are thin, made up of cellulose.
4. Intercellular spaces may be present or absent.
5. Parenchyma performs functions like photosynthesis, storage, and secretion.

Collenchyma :

1. Collenchyma is a living mechanical tissue.
2. It is present below the epidermis in dicot plants.
3. It is present as a continuous hypodermal ring (Eg : Helianthus annus) or as a discontinuous ring (cucurbita)
4. Corners are thickened due to cellulose, hemicellulose and pectin.
5. Intercellular spaces are absent.
6. It provides mechanical support to the growing parts of the plant parts such as young stem, petiole, pedicle etc.
7. In the cytoplasm, if chloroplast is present, photosynthetic in function.

Scelerenchyma :

1. Sclerenchyma is a dead mechanical tissue.
2. Cells are long and narrow.
3. Cell walls are thickened with legnin with pits.
4. They are dead cells. Protoplast is absent.
5. Basing upon the structure, origin and development sclerenchyma are two types – fibres, sclereids.
6. Fibres are thick walled, elongated and pointed cells.
7. Sclereids (stone cells) are spherical, oval or cylindrical shape.
8. Cell walls are highly thickened, lumen is very narrow.
9. Sclereides are found in fleshy fruits like guava, pear and sapota. Seed coat of legumes, leaves of tea, fruit wall of nuts etc.
10. Their main function is to give mechanical support.

Question 4.
What are complex tissues? Describe various types of complex tissues.
Answer:
Tissues which are made up of more than one type of cells and work together as a unit are called complex tissues.

Xylem and phloem are complex tissues.

Xylem :
The main function of xylem is conducting water and minerals from roots to the stem and leaves.

Xylem also provides mechanical strength to plant parts. Xylem consists of (1) Tracheids (2) Vessels (3) Xylem fibres (4) Xylem Parenchyma.

Tracheids :
Tracheids are elongated or tube like cells with thick and lignified walls and tapering ends. These are dead cells without protoplasm. Its main function is water transport.

Vessels :
Presence of vessels is an important character found in angiosperms. Vessels are absent in Gymnosperms. Vessels are dead cells without protoplasm. The cells are elongated or tube like cell thickened with lignin. Its main function is water transport.

Xylem fibres :
These are highly thickened with legnin with narrow central lumen. They may be septate or aseptate.

Xylem Parenchyma :
These are living cells. Cell walls are thickened with cellulose. They store food materials like starch, fats, and tannins. The ray parenchyma cell helps in radial conduction of water.

Primary xylem is of two types – protoxylem and metaxylem.

The first formed primary xylem elementsare called protoxylem. The laterformed primary xylem are called metaxylem.

In stems, protoxylem is towards centre and metaxylem is towards periphery. It is called endarch.

In roots, protoxylem is towards periphery and metaxylem is towards centre. It is called exarch.

Phloem :
The main function of phloem transports food materials usually from leaves to the other parts of the plant body.

Phloem contains (1) Sieve tube elements (2) Companion cells (3) Phloem parenchyma (4) Phloem fibres.

Sieve tube elements :
These are long, tube like structures arranged longitudinally and are associated with companion cells. Their end walls are perforated in sievelike manner to form sieve plates.

A mature sieve tube element possesses a peripheral cytoplasm and a large vacuole but lacks a nucleus. The function of sieve tubes are controlled by the nucleus of companion cells.

Companion cells :
These are specialized parenchymatous cells which are closely associated with sieve tube elements. Both are connected by pit fields present between their common longitudinal walls.

Phloem parenchyma :
These are parenchyma cells in phloem with tapering cylindrical cells which have dense cytoplasm and nucleus. They store food materials and other substances like resin, latex etc.

Phloem fibres (bast fibres) :
These are sclerenchymatous cells. The cell wall is thick. At maturity they lose their protoplasm and become dead.

Question 5.
Describe the internal structure of dorsiventral leaf with the help of labelled diagram.
Answer:
Transverse section of a dicot leaf or dorsiventral leaf shows three parts – epidermis, mesophyll and vascular bundles.

I. Epidermis :
1) It is the outermost layer of leaf with one cell thickness. Cells are barrel shaped. They are arranged compactly without intercellular spaces.
2) Epidermis present on upper (adaxial) side is called upper epidermis. Epidermis on lower (abaxial) side is called lower epidermis.

3) The outer surface of epidermis is covered by a waxy layer called Cuticle.
4) Epidermis shows multicellular hairs.
5) Stomata are present. They are more on lower surface than upper surface.
6) Epidermis gives protection to the inner tissues. Cuticle regulates transpiration. Stomata help in exchange of gases.

II. Mesophyll :

1. Ground tissue present in between the two epidermal layers is called Mesophyll. It is Chlorenchymatous.
2. In dorsiventral leaf, mesophyll is differentiated into two parts – palisade parenchyma and spongy parenchyma.
3. Palisade parenchyma is found beneath the upper epidermis. Elongated and columnar cells are arranged in 1 – 3 rows. Intercellular spaces are narrow. Cells have large number of chloroplasts nearer to the cell wall. (So upper side of leaf is dark green in colour). Palisade tissue is mainly concerned with assimilation of carbohydrates.
4. Spongy parenchyma is found towards the lower epidermis. It has 3-5 rows of irregularly shaped and loosely arranged cells. Intercellular spaces are large. Air cavities are found below the stomata. Cells have less number of chloroplasts. (So lower side of leaf is pale green in colour) Spongy Parenchyma facilitates gaseous exchange. They also help in the synthesis of food materials.

III. Vascular Bundle :

1. Vascular bundles are extended in the mesophyl! in the form of veins.
2. Vascular bundles are bigger at the base of the leaf blade and gradually becomes smaller towards margins and apex.
3. Vascular bundles are conjoint, collateral and closed. Xylem is present towards upper side and phloem towards lower side.
4. Vascular bundles help in conduction of water, mineral salts and food materials.
5. They also provide mechanical strength to the leaf.
6. Each vascular bundle is enclosed by a layer of special mesophyll cells arranged compactly. This layer is called Bundle sheath or Border parenchyma.
7. Ceils of bundle sheath divide and extend towards both epidermal layers. These are called bundle sheath extensions. They help in the conduction of food materials from mesophyll cells to vascular bundles.

Question 6.
Describe the internal structure of an isobilateral leaf with the help of labelled diagram.
Answer:
Transverse section of monocot or isobilateal leaf shows three parts – epidermis, mesophyll and vascular bundles.

I. Epidermis :

1. This is the outermost layer on both sides of the leaf. Cells are one cell in thickness. They are barrel shaped and closely packed without intercellular spaces.
2. It is covered by a waxy layer called cuticle.
3. Epidermis on adaxial (upper) surface is called upper epidermis. Epidermis on abaxial (lower) surface is called lower epidermis.
4. Hairs are absent. Stomata are present on both sides in equal numbers.
5. In grasses specialised cells are present in upper epidermis. They are called bulliform cells or motor cells. They are thin walled and filled with water. They help in rolling and unrolling of the leaf.
6. Epidermis gives protection to inner tissues. Cuticle regulates transpiration. Stomata help in exchange of gases.

II. Mesophyll :

1. Ground tissue present between two epidermal layers is called mesophyll. It is chlorenchymatous.
2. Mesophyll is undifferentiated.
3. Cells have chloroplasts and perform assimilation of carbohydrates.
4. Sometimes patches of sclerenchyma are found beneath the epidermis. They provide mechanical strength.

III. Vascular Bundies :

1. Vascular bundles are present in the mesophyll in the form of veins.
2. Vascular bundles are conjoint, collateral and endarch.
3. Xylem is present on the upper side and phloem is present on the lower side.
4. Veins help in conduction of water, mineral salts and food materials. They also provide mechanical strength.
5. Each vascular bundle is enclosed by a layer of special mesophyll cells called bundle sheath or border parenchyma.
6. Cells present on eitherside of vascular bundles towards upper and lower epidermis are called bundle sheath extensions. In many monocots, they are sclerenchymatous and provide mechanical support.

Question 7.
Distinguish between the following :
a) Exarch and endarch condition of protoxylem
b) Stele and vascular bundle,
c) Protoxylem and metaxylem
d) Interfasicuiar cambium and intrafasicular cambium
e) Open and closed vascular bundles
f) Stem hair and root hair
g) Heart wood and sap wood,
h) Spring wood and autumn wood.
Answer:
a) In roots, the protoxylem lies towards periphery and metaxylem lies towards the centre. Such type of protoxylem is called Exarch, In stems, the protoxylem lies towards the centre (pitch) and the metaxylem lies towards the periphery of the organ. Such type of protoxylem is called Endarch.

b) Stele :
Stele is the central conducting cylinder. Generally it may have pericycle, vascular bundle, medulla and conjunctive tissue or medullary rays.

Vascular bundles :
Xylem and phloem are present in vascular bundles. Xylem conducts water and phloem conducts food materials.

c) Protoxylem :
The first formed primary xylem elements are called protoxylem. Metaxylem : Later formed primary xylem elements are called metaxylem.

d) Intrafasicular cambium :
Cambium present between primary xylem and primary phloem is called Intrafasicular cambium. It is present inside vascular bundle (Intra = Inside; fasicular = vascular bundle)

Interfasicuiar cambium :
The cells in medullary rays become meristematic and forms interfasicuiar cambium (Inter = in between; fasicular = vascular bundle)

e) Open vascular bundle :
The vascular bundle which have cambium betwen xylem and phloem are called open vascular bundle.

Closed vascular bundle :
In these vascular bundles cambium is absent between xylem and phloem.

f) Stem hair and root hair :
Stem hair :
Multicellular hairs present on the stem are stem hair or trichomes. Their main function is to prevent the entry of pathogens.

Root hair :
Unicellular hairs present on the root are root hair. Their main function is absorption of water.

g) Heart wood and sap wood :
Heart wood :
The dark brown coloured central part of secondary xylem comprising of dead elements with highly lignified walls is called heart wood. It is infiltrated with various organic compounds like tannins, resins, oils, gums, aromatic substances and essential oils. The heart wood does not conduct water but it gives mechanical support to the stem.

Sap wood :
The peripheral region of the secondary xylem is lighter in colour and is known as the sap wood. It conducts water and minerals from root to leaf.

h) Spring wood and Autumn wood :

Spring wood	Autumn wood
1. It is produced during spring (favourable) season.	1 It is produced during autumn (unfavourable) season.
2. Xylem vessels have wide lumens.	2. Xylem vessels have narrow lumens.
3. More number of xylem vessels are produced.	3. Less number of xylem vessels are produced.

Question 8.
What is stomata! apparatus? Describe the structure of stomata with a labelled diagram.
Answer:
Structure of stomata :

1. Tiny pores in the epidermis of young aerial parts of the plant are called stomata. Stomata are more abundant in the leaf epidermis.
2. The stoma is bounded by two kidney shaped guard cells in dicots and dumbbellshaped guard cells in monocots. (Eg : grasses).
3. Unlike that of other epidermal ceils, guard cells posses chloroplasts. The wall of the guard cell towards the stomata! pore is thick, while the outer wall is thin.
4. Epidermal cells surrounding guard cells are called subsidiary or accessory cells. They differ from other epidermal cells in their shape and position.
5. The stoma is followed by an air cavity called substomatal cavity in the mesophyll.
6. The stoma, guard cells and subsidiary cells together constitutes stomatal apparatus.

Question 9.
Describe the T.S of a dicot stem. [Mar. ’17 – A.P. ; Mar. ’15 – T.S ; Mar. ’13]
Answer:

Internal structure of primary dicot stem (Helianthus)
A) Ground plan B) Sector enlarged

Internal structure of young dicot stem – Ex : Helianthus annuus

Transverse section of a dicot stem shows three distinct zones – epidermis, cortex and stele.

I. Epidermis :

1. The outermost layer in young dicot stem is called epidermis. It is one cell in thickness.
2. Cells are tubular or rectangular. They are arranged compactly without intercellular spaces.
3. Outer surface of epidermis is covered by a waxy subtance called cutin. This layer is called cuticle.
4. Minute pores found in the epidermis are called stomata.
5. Multicellular hairs developing on the epidermis are called trichomes.
6. Epidermis gives protection to the inner tissues.
7. Stomata facilitates exchange of gases and promotes transpiration.
8. Cuticle and trichomes check transpiration. They also protect the stem from high temperature.
9. Trichomes also help in preventing the entry of pathogenic micro-organisms.

II. Cortex :
It is extrastelar ground tissue. It shows three subzones – hypodermis, general cortex and endodermis.
A) Hypodermis :

1. The layer present below the epidermis is called hypodermis.
2. It consists of 3 – 6 layers of Collenchyma.
3. Cells are arranged compactly without intercellular spaces. They show excessively thickened corners.
4. Hypodermis helps in providing tensile strength to the stem.
5. Hypodermis also helps in production of food materials by having chloroplasts.

B) General Cortex :

1. It is found below the hypodermis.
2. It consists of 5-10 rows of parenchyma.
3. Cells are isodiametric or oval or spherical.
4. Resin or latex ducts may be present in it.
5. Outer layers of cells have chloroplasts and perform assimilation of food materials.
6. Inner layers are concerned with storage of food.

C) Endodermis :

1. It is the innermost layer of cortex.
2. It is in one layer with barrel shaped, compactly arranged cells.
3. Radial and transverse walls show casparian bands.
4. Endodermal cells store starch grains. So it is known as starch sheath.

III. Stele :
Central conducting cylinder is called stele. It occupies major portion of stem. It shows four parts.
A) Pericycle :

1. It is the outermost layer of stele.
2. It lies between endodermis and vascular bundles.
3. It has alternate patches of sclerenchyma and parenchyma.

B) Vascular Bundles :

1. Each vascular bundle is wedge or top shaped.
2. Limited number of vascular bundles are arranged in the shape of a circular ring. Such arrangement is called Eustele.
3. In each vascular bundle the phloem is present outside and xylem towards inside on the same radius. So vascular bundle is conjoint and collateral.
4. Meristematic tissue is present in between xylem and phloem. It is called fascicular cambium. Vascular bundle with cambium is called open type.
5. Xylem is endarch (protoxylem towards centre).
6. Xylem has vessels and xylem parenchyma. Tracheids and fibres are also present. Xylem conducts water and salts.
7. Phloem has sieve tubes, companion cells, phloem parenchyma and fibres. It conducts food materials.

C) Medulla :
Central part of stele is called medulla. It is filled with parenchyma. It is well developed and extensive. It stores food materials.

D) Medullary rays :
Medulla extends to the periphery in between the vascular bundles forming medullary rays. Parenchymatous cells are living, thin walled and elongate radially.

Medullary rays connect stele and cortex. They hlep in lateral conduction.

Question 10.
Describe the T.S of monocot stem. [Mar. ’15 – A.P.]
Answer:
Internal structure of Monocot Stem :
The anatomy of Monocot stem shows four distinct parts – Epidermis, hypodermis, ground tissue, vascular bundles. A distinct cortex is absent. Endodermis, pericycle, medulla, medullary rays are absent.

I. Epidermis :

1. The outermost layer is called epidermis. It is made up of living, rectangular or tabular cells. They are arranged compactly without intercellular spaces.
2. A waxy layer is deposited on the outer surface of epidermis. This is called cuticle.
3. Trichomes are absent. Numerous stomata are found in the epidermis.
4. Epidermis gives protection to inner tissues. Stomata help in exchange of gases. Cuticle prevents evaporation of water.

II. Hypodermis :
It is present beneath the epidermis. It is made up of 1 – 4 rows of thick walled sclerenchymatous fibres. Intercellular spaces are absent. It gives mechanical strength to the stem.

III. Ground Tissue :

1. Tissue next to the hypodermis filling the remaining part of the stem (except vascular bundles) is called ground tissue.
2. It is parenchymatous.
3. Cells are thin walled with or without chloroplasts. They are loosely packed with intercellular spaces.
4. It is mainly concerned with synthesis and storage of food materials.

IV. Vascular Bundles :

1. Numerous bundles are irregularly scattered in the ground tissue. Such an arrangement is called Atactostele.
2. Inner bundles are bigger. Peripheral bundles are small in size. They are oval in shape.
3. Each vascular bundle is enclosed by a sclerenchymatous sheath. So it is called fibro vascular bundle.
4. Each bundle has phloem towards outside and xylem towards inside of the bundle on the same radius. So it is described as conjoint and collateral.
5. Vascular bundles are concerned with conduction of water, salts and food materials.
6. Cambium is absent between xylem and phloem. So the vascular bundle is closed type.
7. Xylem is endarch (protoxylem towards centre). Xylem consists of tracheids, vessels, fibres and xylem parenchyma.
8. Xylem is arranged in the shape of Y. Out of four xylem vessels, two are metaxylem and two are protoxylem vessels.
9. One or two protoxylem vessels are crushed forming lysigenous cavity. It is called protoxylem lacuna. It stores water.
10. Phloem has sieve tubes and companion cells. Phloem parenchyma is absent.

Question 11.
Describe the internal structure of a dicot root. [Mar. – 2018, May ’14]
Answer:
Internal structure of primary dicot root has three zones- epidermis, cortex, stele. Cortex is bigger than stele.

I. Epidermis :

1. It is the outermost layer of thin walled rectangular living cells arranged compactly without intercellular spaces.
2. Cuticle and stomata are absent.
3. Some epidermal cells (trichoblasts) produce tubular extensions called root hairs. Cells giving rise to root hairs are smaller than other epidermal cells. Epidermis of root is called rhizodermis or piliferous layer or epiblema due to the presence of root hairs.
4. Root hairs absorb capillary water. The epidermis gives protection to the inner tissues.

II. Cortex :
Ground tissue system extending from epidermis to stele is called cortex. It is differentiated into three parts.
A) Exodermis :

1. The outermost layer of cortex with 2 or 3 rows of suberised thick walled cells is called exodermis.
2. It acts as a protective layer when epidermis is removed.
3. It prevents the exit of water from cortex.

B) General cortex :

1. It is present beneath the exodermis.
2. It has several layers of loosely arranged thin walled parenchyma. Intercellular spaces are present.
3. Cells store food materials.
4. General cortex helps in the lateral conduction of water from epidermis to xylem vessels.

C) Endodermis :

1. It is the innermost layer of cortex.
2. It is made up of single layer of barrel shaped cells.-
3. Radial and transverse walls of endodermal cells show thickenings due to deposition of lignin and suberin. These are called casparian thickenings. It is characteristic feature of endodermis.
4. Endodermal cells present opposite to protoxylem are thin walled without casparian strips. These cells are called passage cells.
5. Passage cells help in the entry of water and salts from cortex into stele.

III. Stele :
The central conducting cylinder is called stele. It shows three parts.
A) Pericycle :
It is the outer layer of the stele. It is uniseriate with thin walled rectangular parenchymatous cells. Pericycle gives rise to lateral roots. It also helps in secondary growth.

B) Vascular bundles :

1. Xylem and phloem are arranged alternately on separate radii. So vascular bundles are separate or radial. Xylem and phloem conduct water and food materials respectively.
2. Protoxylem is towards pericycle and metaxylem towards centre. So xylem is exarch.
3. Xylem is variable from monarch to octarch (xylem groups 1-8) usually tetrarch (4 xylem groups alternating with 4 phloem bundles). Monarch – Trapa, Tetrarch – Gossypium. Octarch – Castanea.
4. Cambium is absent.
5. Parenchyma tissue extending between xylem and phloem strands is called conjunctive tissue. It helps in the storage of food materials.

C) Pith or Medulla :
The central portion of stele is called medulla or pith. It may be completely absent in dicot root. When it is present, it is parenchymatous. It helps in the storage of food and water.

Question 12
Describe the internal structure of a monocot root. [Mar. ’20, May. ’17]
Answer:
Internal structure of monocot root is differentiated into three zones – epidermis, cortex and stele.

I. Epidermis:

1. The outermost layer is called epidermis. Cells are living, rectangular, thin walled. They are compactly arranged without intercellular spaces.
2. Cuticle and stomata are absent.
3. Some cells (trichoblasts) show tubular extensions – root hairs. Epidermis of root having root hairs is called epibiema or piliferous layer or rhizodermis.
4. Root hairs help in the absorption of capillary water form the soil. Epidermis gives protection to the inner tissues.

II. Cortex :
This is the ground tissue system extending from epidermis to stele. It is differentiated into three parts.
A) Exodermis :

1. It is the outermost layer of the cortex with 2 or 3 rows of cells. Cell walls are thick and suberised.
2. It acts as a protective layer when epidermis is removed.
3. It prevents the exit of water from cortex.

B) General cortex :

1. It is present beneath the exodermis.
2. It has several layers of loosely arranged thin walled parenchyma. Intercellular spaces are present,
3. Cells store food materials.
4. General cortex helps in the lateral conduction of water from epidermis to xylem vessels.

C) Endodermis :

1. It is the innermost layer of the cortex.
2. It is made up of a single layer of barrel shaped cells.
3. Radial and transverse walls of endodermal cells show thickenings due to the deposition of lignin and suherin. These are called Casparian thickenings.
4. Endodermal cells present opposite to protoxylem are thin walled without casparian strips. These cells are called passage cells.
5. Passage cells help in the entry of water and salts from cortex into stele.

III. Stele :
The central conducting cylinder is called stele. It is very prominent and bigger in size. It shows three parts,
A) Pericycle :

1. It is the outermost layer of the stele. It is uniseriate with thin walled parenchymatous cells.
2. Pericycle gives rise to lateral roots.
3. In old roots it becomes sclerenchymatous and gives mechanical strength.

B) Vascular bundles :

1. Xylem and phloem are arranged alternately on separate radii. So vascular bundles are radial or separate.
2. Protoxylem is towards pericycle and metaxylem towards centre. So xylem is exarch.
3. Xylem is polyarch (numerous xylem groups).
4. Cambium is absent.
5. Xylem is concerned with conduction of water and salts. Phloem conducts organic solutes.
6. Parenchyma tissue extending between xylem and phloem strands is called conjunctive tissue. Cells are rarely thick walled. It is helpful in storage of food and provides mechanical strength.

C) Medulla or pith – The central part of stele is called medulla or pith. It is conspicuous. It is parenchymatous. It helps in storage of food. In some plants cell walls are lignified providing mechanical strength.

Intext Question Answers

Question 1.
Name the various kinds of cell layers which constitute the bark.
Answer:
Periderm and secondary phloem.

Question 2.
Every 50 years, for 200 years, a nail was drilled into a tree to the same depth and at exactly 1m above the sail surface (assuing the ground level has not changed). What will be the pattern of the four nails on the tree ? Do you know the reason for your answer ? If yes give the reason.
Answer:

1. The heads of all the four nails are at same level.
2. Stem of plant undergoes later growth due to cambial activity. Hence, growth (circumference) of stem increases.
3. All the four nails will be seen in the xylem portion of the stem.
4. There will not be change in nail position with respect to vertical position from ground level. Because the vertical growth is reduced after some period and lateral growth is promoted in plant.

Question 3.
Why is wood made of xylme and not a phloem?
Answer:

1. Cambial ring produces more xylmen than phloem during secondary growth.
2. Xylem with the exception of parenchyma, consists of dead tissues i.e., tracheids, vessels and fibres.
3. Phloem is living complex tissue, with the exception of fibres (bast).
4. Hence wood is made of xylem.

Question 4.
A student estimated the age of a tree to he about 300 years. How did he anatomically estimate the age of this tree?
Answer:
The age of a plant can be estimated by counting the number of annual rings.

Question 5.
Assume that you have removed the duramen part of a tree. Will the tree survive or die?
Answer:
The plant survives because of the presence of sapwood which is meant for the conduction of water and minerals. Duramen is not useful for conduction.