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Anatomy of Monocot and Dicot Root


Internal Structure of Dicot Root

Internal structure of a typical dicotyledon  root shows following features :-

1. Epiblema

It is uniseriate outermost layer. It comprising tubular living components. Cuticle and stomata are absent. Unicellular root hairs are formed due to elongation of some cells of epiblema. Epiblema also known as Rhizodermis or Piliferous layer. Root hair are present in  maturation zone of root.
 Note: Cells of epiblema which develop root hair called trichoblast.

2. Cortex

It is  made up of parenchymatous cells.  Chloroplast is absent so they are non-photosynthetic but chloroplast is present in roots of Tinospora andTrapa so they are photosynthetic.

Note : The cells of outer part of cortex become suberized (mainly) or cutinized in old root. It is called exodermis. Exodermis found in some dicotyledonae roots and most of the monocotyledonae roots.

3. Endodermis

This layer is situated between the pericycle and cortex. Casparian strips are present on radial and tangential wall of endodermis. These strips are made up of ligno suberin (mainly suberin). Casparian strips are discovered by Caspari.

EndodermisEndodermisThe cells of endodermis which are situated in front of protoxylem cells lack of casparian strips. These are called passage cells/ transfusion cells. 

  • The number of passage cell are equivalent to the number of protoxylem cells.  
  • Passage cells provide path to absorbed water from cortex to pericycle.

Note:

(1) Casparian bands and passage cells are well developed in monocot root in comparison to dicot root.

(2) Endodermis acts as a watertight jacket

(3) Casparian bands are also present in dicot stem but they are less developed.

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4. Pericycle

It is single layered and composed of prosenchyma.

Lateral roots are usually originated from the part of pericycle which is lying opposite to protoxylem. Thus lateral roots are endogenous in origin.A few mature cells of pericycle usually opposite to protoxylem, become meristematic. These cells divide by periclinal divisions and form some layers of cells. These divisions are followed by anticlinal divisions forming a lateral root primordium which grows to form a lateral root.

Note

(i) The branches of stems are exogenous in origin because these are originated from extra stelar region .

(ii) Adventitious root are also endogenous. because these are originated from stelar region (phloem parenchyma or inner to endodermis or pericycle).

5. Vascular Bundles

Vascular bundles are radial and exarch. xylem and phloems are separate and equal in number. The number of xylem bundles are two to six (diarch to hexarch). But exceptionally, Ficus (Banyan tree) root is polyarch. Parenchyma which is found between xylem and phloem, called Conjunctive tissue.

6. Pith

In dicot root pith is less developed or absent.

Internal Structure of Monocot Root

The internal structure of a typical monocotyledon root is similar to dicotyledon root.

But 

(1) Number of xylem bundles are more than six (Polyarch) in monocotyledon root (exceptionally the number of xylem bundles are two to six in onion )

(2) Pith is well developed in monocotyledon root

Monocotyledon RootMonocotyledon Root

Anatomy of Monocot and Dicot Stem

Internal Structure of Dicot Stem

Internal structure of a typical dicot stem shows following features :-

1. Epidermis

Epidermis is the outermost layer of the stem. It is single layered and lack of chloroplast. Stomata multicellular hairs(trichomes) are present on epidermis. Cuticle is present on epidermis.

 Epidermis plays a significant role in protection.

2. Cortex

In dicotyledon stem cortex divided into three parts :

(a) Hypodermis (b) General Cortex (c) Endodermis

(a) Hypodermis : It is present just below the epidermis. It provides additional support to epidermis. It  is thick multicellular layer. This layer is composed of collenchyma and their cells also contain chloroplast.

(b) General Cortex : This part is composed of parenchyma. Storage of food is the main function of the cortex. Resin canal/mucilage canal are present in it. These are schizogenous in origin. The innermost layer of the cortex is called endodermis.

(c) Endodermis : It is single celled thick layer. The cells of endodermis are barrel shaped. These cells accumulate more starch in stem of dicot. Thus , it is known as "starch sheath".

3. Pericycle   

This layer situated in between the endodermis and vascular bundles. The pericycle of stem is multilayered and made up of sclerenchyma. Sclerenchymatous pericyle is also known as Hard bast.

Note : In sunflower stem, pericycle is made of alternate bands of parenchymatous and sclerenchymatous cells. The part of pericycle which is present in front of the vascular bundle is made up of sclerenchyma and remaining part is composed of parenchyma. Part of pericycle which is situated in front of vascular bundle is known as Bundle cap. In sunflower stem, pericycle is heterogenous in nature.

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

4. Vascular Bundle 

The vascular bundles (wedge shaped) are arranged in a ring. Each vascular bundle is conjoint, collateral and open and xylem is endarch.

5. Pith

This is well developed region, spreading from ring of vascular bundle to the centre. The cells of this region mainly made up of parenchyma.

Note: The part of pith which is radially arranged between the vascular bundles, called pith rays or medullary rays.
The main function of pith rays is radial conduction of food and water.

Internal Structure of Monocot Stem

 

1. Epidermis

Epidermis is the outer most single celled thick layer. It is covered with thick cuticle. Multicellular hairs are absent & stomata are also less.

2. Hypodermis 

Hypodermis of monocotyledon stem is made up of sclerenchyma. It is 2-3 layered. In monocot stem rigidity is more in hypodermis where as in dicot stem elasticity is more. It provides mechanical support to plant.

3. Ground Tissue

The entire mass of parenchyma cells next to hypodermis and extending to the centre is called ground tissue. There is no differentiation of ground tissue in monocotyledon stem. It means ground tissue is not differentiated into endodermis, cortex, Pericycle etc.

Note : Sometimes in some grasses, wheat etc. the central portion of ground tissue becomes  hollow and is called pith cavity.

4. Vascular Bundle

Many vascular bundles are scattered in the ground tissue and V.B. are generally oval shape.
Vascular bundles lies towards the centre are large in size and less in number.
Vascular bundles situated towards the periphery are small in size but more in number.
Each vascular bundle is conjoint collateral and closed and xylem is endarch. Each Vascular bundle is surrounded by fibrous sclerenchymatous bundle sheath. So vascular bundles are called fibro vascular bundles.

(a) Xylem :- In xylem number of vessels is less. In metaxylem there occur two large vessels while in protoxylem there occur one or two small vessels. Vessels are arranged in V or Y shape. Just beneath protoxylem vessels, there occur a water cavity which is schizolysigenous in origin but major part of water cavity is lysigenous. This cavity is formed by disintegration of the element present below the protoxylem and neighbouring parenchyma.
Exception : In Asparagus water cavity & bundle sheath are absent.

(b) Phloem :- It consists of sieve tube elements and companion cells. Phloem parenchyma is absent.

 5. Pith

Pith is undifferentiated  in monocotyledon stems.

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

Anatomy of Monocot and Dicot Leaf

Internal Structure of Leaf

Generally leaves divided into two categories - dorsiventral leaves and isobilateral leaves. 
The differences in between them as follows :

Dorsiventral or Bi–facial

Iso–bilateral or Equi-facial

1. Present at right angle to stem 

1. Arranged parallel to stem.

2. Upper surface of leaf receive more sun light as compared to lower surface, so there occur difference between internal structure of upper and lower surfaces Example :- Dicots Exception - Eucalyptus and Nerium leaves are Iso-bilateral.2. Both surfaces of leaf receive equal amount of sun light so there occur no difference between internal structure of upper & lower surfaces. Example :- Monocots Exception - In Lilium longiflorum leaves are dorsiventral


Internal Structure of Dorsiventral Leaves

  •  Cuticle is present on both surfaces but cuticle on upper surface is more thick.

  •  In dorsiventral leaves stomata more on lower surface and stomata on upper surface is absent or less in number

  •  Mesophyll is differentiated into Palisade tissue and spongy tissue.  Palisade tissue is situated towards upper (adaxial) surface.These cells are elongated, arrange vertically and parallel to each other and have more chloroplasts and a large vacuole.

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

  •  Spongy tissue is situated towards lower (Abaxial) surface. The cells are oval or rounded and between cells large air space are present.

Internal Structure of Isobilateral Leaves

  •  The thickness of cuticle is equal on both surfaces.  

  • Usually stomata on both surface's are equal in number. 

  • Mesophyll is not differentiated into palisade and spongy tissues in isobilateral leaves. Mesophyll cells have only a few intercellular spaces.

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

Note :

(1) In isobilateral leaf, two distinct patches of sclerenchyma are present above and below each of the large vascular bundles and extend up to the upper and lower epidermal layers, respectively.

(2) In dorsiventral leaf, two distinct patches of parenchyma (mainly)/collenchyma are present above and below each of the large vascular bundles and extend up to the upper and lower epidermal layers, respectively. Chloroplasts are absent in bundle sheath extensions.


Vascular Bundles of Leaves

 

  • Similar types of vascular bundles are found in both dorsiventral and isobilateral leaves. Vascular bundles of leaves are conjoint, collateral and closed and xylem is endarch (mostly).
  • Protoxylem is situated towards the adaxial surface and protophloem towards the abaxial surface in the vascular bundle. Leaves are devoid of endodermis and pericycle. Vascular bundles are surrounded by a bundle sheath. It is made up of parenchyma (mostly) or sclerenchyma.

 Note : 

1. In the leaves of C4-plants, bundle sheath is chlorenchymatous

2. In grasses, certain adaxial epidermal cells along the veins modify themselves into large, empty, colourless cells. These are called bulliform cells  or motor cells . When the bulliform cells in the leaves have absorbed water and are turgid, the leaf surface exposed. When they are flaccid due to water stress, they make the leaves curl inwards to minimize water loss.
Example :- Ammophila, Poa, Empectra and Agropyron etc. are Psammophytic grasses

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

 

2. Both upper & lower epidermis of Nerium leaves are multilayered and in Ficus leaves upper epidermis is multilayered. This is an adaptation to reduce transpiration.

1.Xerophytes with isobilateral leaves contain palisade tissue on both sides of leaf.
Example :- Eucalyptus & Nerium.

2. Desert grasses contain palisade like spongy tissue.

3. Unifacial or cylinderical leaf :- In these leaves there occur no differentiation of upper surface and lower surface. Example :- Onion, Garlic.

4. Albascent leaf :- Palisade tissue is restricted in half part of leaf so half part appears more green and other half appears less green. Example : Abutilon


Old NCERT Syllabus

Root

INTERNAL STRUCTURE OF ORCHID ROOT

Velamen :- It is found in aerial or hanging roots of some epiphytes (eg. orchid)

  • It is an example of multilayered epidermis
  • It is present outside the exodermis. It is derived from protoderm. It is dead tissue.
  • They absorb atmospheric moisture by imbibition. l Spiral thickening of colloids is found in velamen cells.

Passage cells are found in both exodermis and endodermis in hanging roots of orchids.

 

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

Fig: Orchid rootFig: Orchid root

Stem

CUCURBITA STEM :-

  • It contains five ridges and five furrows. The vascular bundles arranged in two rows. Each ring has five vascular bundles. In this way the total 10 vascular bundles are present.

  • The vascular bundles of outer ring are small in size and situated in front of ridges while the vascular bundles of inner rings are large in size and located below the furrows.

  • Vascular bundles are conjoint, bicollateral and open and xylem is endarch.

  • Hypodermis is absent or less developed in furrows region and general cortex contains chloroplast.

  • In Cucurbita stem pericycle is sclerenchymatous.

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf | Biology Class 11 - NEET

 

Leaves

ANOMALOUS PRIMARY STRUCTURE

[1] ANOMALOUS STRUCTURE IN DICOTYLEDON STEM

I. Scattered Vascular Bundles :- In some of dicotyledon stem, vascular bundles are not arranged in a ring, they are scattered in the cortex. Example :- Thallictrum, Nymphaea, Papaver orientale & Peperomia.

II. Phloem on innermost radius :- Generally, phloem is situated in the ring of vascular bundles towards peripheral (outer) radius and xylem towards the inner radius. But anomalously in some plants, the position of phloem is towards the inner side of xylem. Such type of phloem is called Internal phloem. Because, this phloem lies towards the pith, so it is also known as medullary phloem.
This anomalous condition is found in Calotropis, Capsicum, Leptadaenia, etc. plants.

III. Medullary Vascular Bundles :- In addition to normal ring of vascular bundles, some vascular bundles are also present in pith. These are called medullary vascular bundles.
Example : Amaranthus, Boerhaavia, Chenopodium, Mirabilis, Achyranthes, Bougainvillea , Raphanus sativus.

IV Cortical Vascular Bundles :- In addition to normal ring of vascular bundles, some vascular bundles are also present in the cortex. They are known as cortical vascular bundles.
Example :- Casuarina, Nyctanthes and Lathyrus.etc.

V. Polystelic condition :- It is the normal situation in pteridophytes but in some dicotyledons it is present abnormally.
Example :- Primula, Dianthera

VI Exclusively xylem vascular Bundle :- Abnormally, some vascular bundles are only formed by xylem except the normal vascular bundles.
Example :- Paeonia

VII Exclusively phloem vascular Bundle :- Abnormally, some vascular bundles are only formed by phloem except normal vascular bundles in some plants Example :- Cuscuta & Ricinus communis

[2] Anomalous structure in monocot stem :–

Normally vascular bundles are found in monocotyledon stems in scattered form but in the stem of some monocotyledon plants vascular bundles are arranged in rings. Ex. Members of family Gramineae, such as Triticum, Secale, Hordeum, Avena, Oryza etc.

(1) Cricket bat → from Salix [Willow]

(2) Hockey→ from Morus [Mulberry]

(3) Monarch Condition →in Trapa root

(4) Triarch Condition→ in Pisum root

(5) Tetrarch Condition→ in Helianthus annuus (Sunflower) and Cicer arietinum (Gram) root

(6) Waiting meristem concept :- This concept was given by Buvat. According to this, there is  an inactive centre in the shoot apex which is known as waiting meristem and it acts as reservoir of active initials and on induction it give rise to reproductive apex.

(7) Tannin is found in latex of banana.When it comes in contact with air it gets oxidised and becomes reddish brown in colour

(8) Chewing gum is made by latex of Achras sapota.

(9) Tannin glands are found in camellia. These glands are schizogenous in origin

(10) Salt glands are found in Tamarix which secretes sodium chloride.

(11) Chalk glands are found in plants of plumbaginaceae family which secretes calcium carbonate.

(12) Multilayered (14 to 15 layers) epidermis is found in Peperomia leaves.

(13) Cystolith containing cells are found in the upper epidermis of Ficus leaf, called lithocytes/Lithocysts.

(14) Lignin is stained by safranin.

(15) Tracheids are the chief water transporting elements in gymnosperms.

(16) Phloem is embedded into the secondary xylem in some plants. Such phloem is called included phloem or interxylary phloem. This is secondary anomalous structure.
Example :- Leptadaenia, Salvadora etc. dicot stem.

(17) Pericycle is absent in roots and stems of some aquatic plants.

(18) In some monocotyledonae roots, pith is sclerenchymatous. Ex. Canna

(19) A nectar secreting gland cell contains granular cytoplasm and a large conspicuous nucleus.

(20) Transition of exarch bundles of root to endarch bundles of stem occurs in hypocotyl.

(21) In leaves, the ground tissue consists of thin walled chloroplast containing cells and is called mesophyll.

(22) The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus.

(23) The size of vascular bundles are dependent on the size of the veins. The veins vary in thickness in the reticulate venation of the dicot leaves.

(24) The parallel venation in monocot leaves is reflected in the near similar sizes of vascular bundles (except in main veins) as seen in vertical sections of the leaves. 

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FAQs on Anatomy of Monocot & Dicot Plants: Root, Stem & Leaf - Biology Class 11 - NEET

1. What is the difference between monocot and dicot roots?
Ans. Monocot roots have a pith in the center and a ring of xylem and phloem arranged in a circular pattern, while dicot roots have a central core of xylem surrounded by phloem. Additionally, monocot roots have a fibrous root system with numerous thin and branching roots, while dicot roots have a taproot system with a main central root and smaller lateral roots.
2. How does the internal structure of dicot roots differ from monocot roots?
Ans. In dicot roots, the xylem and phloem are arranged in a central core, with the xylem forming a star-like pattern in the center and the phloem surrounding it. On the other hand, monocot roots have a ring-like arrangement of xylem and phloem, with the xylem forming a hollow cylinder in the center and the phloem surrounding it.
3. What is the internal structure of dicot stems?
Ans. The internal structure of dicot stems consists of a central pith surrounded by alternating layers of xylem and phloem. The xylem forms a star-shaped pattern with the pith at the center, while the phloem is located in between the arms of the xylem. The outermost layer of the stem is the epidermis, followed by the cortex and the pericycle.
4. How is the internal structure of monocot stems different from dicot stems?
Ans. Unlike dicot stems, monocot stems do not have a distinct pith in the center. Instead, they have scattered vascular bundles consisting of xylem and phloem throughout the stem. The vascular bundles are surrounded by ground tissue and are arranged in a scattered pattern, giving the stem a uniform appearance.
5. What are the different types of leaf internal structures?
Ans. Leaves can have two types of internal structures - dorsiventral leaves and isobilateral leaves. Dorsiventral leaves have distinct upper and lower surfaces, with the upper surface containing more chlorophyll for photosynthesis. Isobilateral leaves, on the other hand, have similar upper and lower surfaces, with chlorophyll evenly distributed throughout the leaf.
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