Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

Biology Class 11

NEET : Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

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PERMANENT TISSUES

Permanent tissues are composed of cells which have lost the power of division temporarily or permanently.

They are formed by division and differentiation of meristematic tissues.

  •  Their cells may be living or dead. Permanent tissues are of three types :-

A. Simple tissue (Homogenous tissue)

B. Complex tissues (Heterogenous tissue)

C. Special tissue

[A] Simple tissues These tissues are made up of similar type of cells or only one type of cells that perform a common function.

Simple tissues are of three types :-I. Parenchyma II. Collenchyma III. Sclerenchyma  

I. Parenchyma : It is very primitive type of tissue. It is first evolved tissue. Remaining all different types of tissues are derived from this tissue.  so it is also called as fundamental tissue l Parenchyma name coined by Grew.

CHARACTERISTIC FEATURES :

  • It is a living tissue.
  •  It is first differentiated tissue derived from meristem.
  •  It is a universal tissue.
  •  Flesh of a fruit is mainly composed of parenchyma.
  •  Body of bryophyte plants is mainly composed of parenchyma.
  •  Parenchyma is most common tissue which is morphologically and physiologically unspecialized.
  • The cells of parenchyma are thin walled. Cell wall is made up of pectocellulose (mainly cellulose). So parenchyma is a soft tissue.
  •  Each cell containing large central vacuole. So the main function of a parenchyma cell is storage of food.
  •  Usually Inter cellular spaces are present between cells of this tissue, it is a loose tissue. Intercellular spaces are usually schizogenous in origin.
  •  The cells are usually isodiametric.

 

Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

 

SHAPE :

  • The cells of parenchyma are spherical, oval or polygonal  in shape. Each parenchymatous cell  contains 14 planes of lateral line, which are maximum possible plane in a cell.  These are known as tetrakaidecahedron.

MODIFICATIONS OF PARENCHYMA :
1. Prosenchyma :- The cells of this parenchyma are long with pointed ends. This parenchyma forms the pericyle of roots. Function : Provide support to plant organ.

2. Aerenchyma :- This parenchyma is made up of rounded cells. These cells surrounds the large air chambers.
Air chambers are lysigenous in origin. Aerenchyma is found in cortex region. It provide buoyancy to hydrophyte plants.

3. Stellate parenchyma :

  • The cells of this tissue are stellate and branched. Air spaces are also present but they are less developed.  Main function of this parenchyma is to provide mechanical support and provide mechanical strength to leaf bases of banana.

4. Chlorenchyma : Such type of parenchyma in which abundant quantity of chloroplasts are found. Two types of chlorenchyma are present in dorsiventral leaves :-

(a) Palisade tissues :- Inter cellular spaces are absent. Their cells are tightly fitted together. They are present towards adaxial/ ventral/upper side of leaf. Number of chloroplasts are more in palisade tissue as compare to spongy tissue. So upper surface of a leaf appears more green as compared to lower surface.

(b) Spongy tissues :- Large intercellular spaces are present. So they facilitates transpiration and gaseous exchange.They are present towards abaxial/dorsal/lower side of leaf.

5. Mucilage Parenchyma : In the Mucilage parenchyma large vacuoles and Mucilage will be found. e.g. Succulent xerophytic plants. e.g. Aloe. Function -storage of water.

Functions of parenchyma :

1. The main function of this tissue is storage of food.

2. Some cells of parenchyma store waste materials. They are called "idioblast cells". Idioblast cells store  oils, tannin and crystal of calcium oxalate .

II COLLENCHYMA : Term coined by Schleiden.

Main characteristics :

  •  Collenchyma is a living mechanical tissue. Lignin is absent.
  •  It is made up of elongated (In transverse section cells are oval, spherical or polygonal in shape) cells.
  •  localized deposition of pectocellulose (mainly pectin) & hemi cellulose is the characteristics feature of collenchyma.
  •  Usually intercellular spaces are absent.
  •  Vacuolated cytoplasm is found in the cells of collenchyma . Chloroplast may be found in the cells of collenchyma.

 

Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

Occurence :

  • Collenchyma is not a universal tissue. It is found in the stems of herbaceous dicotyledons below epidermis either as a homogenous layer or in patches.
  • Collenchyma is absent in woody plant parts (After secondary growth in plant parts), roots and monocotyledons.
  • Collenchyma forms the hypodermis of dicotyledon stems. Cells of collenchyma are flexible due to hydrophilic nature of pecto-cellulose so flexibility occurs in dicotyledonae stems.
  • Lamina margins of leaves also bears collenchyma. This protects the cracking of lamina margin due to the action of wind.

TYPES OF COLLENCHYMA :
On the basis of place of deposition, it is classify into three types by majumdar :-

1. Lamellar/plate collenchyma :- The cells of collenchyma arranged in lamellar forms. The cell have thickening on the tangential walls. Due to such type of deposition, cell looks like a lamellar or plates. Ex. Sunflower stem.

2. Angular collenchyma :- This type of collenchyma abundantly found in plants. The cells of this tissue are angular. The deposition of pectocellulose at the angles of cell wall. e.g., Stem of Datura, Solanum and tomato

3. Lacunar collenchyma/tubular collenchyma :- Large intercellular spaces are present in the cells of this tissue. Deposition of pectocellulose on the walls of intercellular spaces. e.g. Cucurbita stem and aerial roots of Monstera.

FUNCTIONS

  • Mechanical as well as biological. It provides tensile strength for extensibility of various growing plant organs/provide tensile strength/provide tensile strength against bending & swaying.
  • Due to the presence of chloroplast, photosynthesis process takes place in collenchyma.

III SCLERE NCHYMA
Name coined by Mettenius. – Main features :-

  • Sclerenchyma is the main mechanical tissue.
  •  These cells are long, narrow, thick walled, lignified and dead.

Function :

  • It provide mechanical support/mechanical strength to plants.
  • Various types of pits are formed due to the deposition of lignin on hard wall.

Types of sclerenchyma On the basis of length of cells and amount of deposition of wall materials (Lignin). Sclerenchyma cells are of two types.

(i) Sclereids (ii) Sclerenchymatous fibres

I. Sclereids : These cells are small, extremely thick walled and their ends are not pointed. Sclereids are isodiametricorirregular in shape. Sclereids cells have more pits and lumen is almost very small.

Their pit cavity is branched.

  •  Sclereids are classify by Tschierch, on the basis of their shapes :-

Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

(A) Stone cells or Brachy- sclereids or Grit cells:-These cells are spherical or oval in shape. They are found in endocarp of drupe fruits, so endocarp becomes hard. *

  • They are present in endocarp of Coconut, Mango, Almond, Walnut etc.
  • Brachy sclereids are also present in fleshy (edible) part of pear (Pyrus). Grittness in pear fruit is due to these sclereids.
  • Brachy sclereids are also found in pulp of guava' and sapota.

 (B) Trichosclereids : These are also known as internal hairs. They are spines like, bifurcated cells. These are found in floating leaves of hydrophytes.

 (C) Astro Sclereids or Stellate sclerenchyma : These cells are stellate (star) shaped. They are found in floating leaves.

Example :- Both Astro and Tricho sclereids are present in floating leaves.
Victoria, Nelumbo ( Lotus) and in Nymphaea petiole.

 Note – Astro sclercids are also found in tea leaves.

(D) Macro-sclereids or Rod cells or Malpighi cells :-They are small and rod like cells. They are present in seed coats. Ex. legume seeds.

  •  In leguminous plants, hardest seed coat is found in french bean (Phaseolus vulgaris). 

(E) Osteo- Sclereids :-These are known asprop-cells. These are pillar like cells. Both end of pillar like cells spreads to form bone like structure.

Example :- These cells are found in leaves of Hakea and Osmanthus.

II SCLERENCHYMATOUS FIBRES

  •  These cells are fibrous. They are longest cells in plant body. Their both ends are pointed (tapering). Due to thick cell wall, lumen is reduced.

  •  Their cell wall contains simple and bordered pits.

Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

Doc: Permanent Tissues - Types Parenchyma NEET Notes | EduRev

 On the basis of structure fibres are classified into two groups :-

(a) Libriform fibres :- They are highly thickened long fibres. They posses simple pits and narrow lumen.
Libriform fibres are found in phloem, xylem, pericycle and hypodermis (Maximum in phloem).

(b) Fibre Tracheids :-  They are also highly thickened. Bordered pits are present in these fibres and lumen is broad. They are only found in xylem.

  •  On the basis of position, fibres are divided into three types -

A. Surface fibres :- They are present on the surface of plant. These fibres also called as filling fibres.

(i) Seed surface fibre 

Example 1 : Cotton fibres - Cotton fibres are out growth of seed coat/out growth of testa. Cotton fibres are composed of cellulose. They are non-lignified. So cotton fibres are not true fibres. Two types of fibres are found in cotton. Long fibres are called 'lint' and small fibres are known as'fuzz'. Lint fibres are used in cloth industry. Fuzz are filling fibre.

Example 2 :  Red silk cotton (Semal fibre) - Obtained from Salmalia malabaricum

Example 3 :  White silk cotton (Kapok) - Obtained from Ceiba pentendra (Both red and white silk cotton fibres are not true fibres and they are also an example of seed surface fibre.)

(ii) Coir of coconut is also a type of surface fibre. They are derived from the mesocarp. These are true fibres, becouse they are lignified.

B. Xylary or wood fibres :- These are hard fibres. They fibres are not flexible. They can not be knitted (weaved) easily so they are not useful. These are obtained from xylem.
Ex. Munj fibre (Saccharum munja)

C. Bast fibres/Extra xylary fibres/Phloem fibre :- These are also known as commercial fibres. These fibres are flexible and can be knitted (weaved) easily. They have great economic value.

  • These fibres are obtained from the phloem and pericycle of plants. 
  • The bast fibres of Corchorus capsularis.(Jute),Crotalaria juncea (Sunn hemp) and Hibiscus sabdariffa (patua) are obtained from the secondary phloem of stem.
  • The bast fibres of hemp (Cannabis sativa) and Linum usitatissimum(flax) are obtained from the pericycle.

Fibres which are obtained from pericycle are called perivascular fibres.

Leaf fibres ⇒ Manila hemp (Musa textilis) and agave hemp (Agave sislana):- These are obtained from sclerenchymatous bundle sheath.

  • Fibres are longest plant cell. Longest fibres occur in Boehmeria nivea (Ramie fibre) length–55 cm. 
  • In plant kingdom hardest and thickest (Largest) leaves are found in Victoria regia due to presence of astrosclereids. Diameter ( 1–1.5 m) 
  • Longest leaves are found in Raphia vinifera. Length 10 – 15 m.
  • Longest commercial fibres – Jute fibres
  • Sclerenchyma is classified on the basis of variation in form, structure, origin and development.
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