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Saturday, March 2, 2019

Permanent tissue: Types and Functions of simple permanent tissue

Permanent tissue: characteristics, types, and functions

 💙 Consists of cells which have lost the power of division temporarily or permanently.

💙 Formed by differentiation of meristematic tissues.
💙 Maybe living or dead.
💙 Cells of permanent tissue are arrested at the Go or G1 stage of the cell cycle.
💙 Made up of mature cells.

Types of permanent tissue

        ➤ Simple permanent tissue or homogenous tissue.

        ➤ Complex permanent tissue or Heterogenous tissue.
        ➤ Special tissue or Secretory tissue.

Simple permanent tissue or Homogenous tissue

Simple permanent tissue is made up of structurally similar types of cells that perform a common function.

⚈ Simple permanent tissue is of the following 3 types.

        1) Parenchyma

        2) Collenchyma

        3) Sclerenchyma

⚈ Very primitive and first evolved tissue.

⚈ All other tissues are derived from parenchyma, so it is also known as fundamental tissue or precursor of all other tissues.

⚈ Termed by N. Grew.
⚈ Present in almost all the parts of a plant like a root, stem, leaves etc and is thus a universal tissue.
⚈ Living tissue.
⚈ First differentiated tissue.
⚈ Living tissue.

⚈ The pulp of fruits and body of bryophytes mainly contains parenchyma.

⚈ Living storage tissue of thin pectocellulosic cell wall i.e. pectin and cellulose.
⚈ Each cell has a large central vacuole and thus associated with the storage of food.

⚈ No or small intercellular spaces. [Spaces if present is schizogenous in origin.]
⚈ The most common tissue and is morphologically as well as physiologically unspecialized.
⚈ Cells are isodiametric.
⚈ Parenchymatous cells are spherical, oval and polyhedral in shape.
⚈ Found in the cortex, pericycle, mesophyll of leaf, floral parts, pith, medullary rays etc.
⚈ Each cell has a large central vacuole and thus associated with the storage of food.

Modifications of parenchymatous tissue

 a) Prosenchyma: Fibre-like elongated, pointed and thickly walled parenchyma is prosenchyma. It provides mechanical support and is present in the pericycle of the root.

 b) Aerenchyma: Made up of round or spherical cells that surround large air chambers. Found in the cortex region of hydrophytes and thus provides buoyancy to them.
c) Chlorenchyma: Found in the mesophyll of leaf and contains abundant chloroplasts and thus performs photosynthesis.
d) Stellate parenchyma: Contains star-shaped cells, found in the leaf base (pseudostem) and petiole of banana leaves to provide mechanical support to them.
 e) Mucilage parenchyma: Large vacuoles and mucilage are present just to bring water storage.Found in the succulent plant like Aloe, opuntia, Euphorbia etc
Functions of Parenchyma
⚈ Some parenchymatous cells store waste materials called idioblasts.
The idioblasts store tannins, oils, calcium oxalate crystals etc.

⚈ As chlorenchyma, it performs photosynthesis.

⚈ As Aerenchyma provides buoyancy to hydrophytes.
⚈ As prosenchyma, stellate parenchyma it provides mechanical support.
⚈ As mucilage parenchyma stores water.
⚈ Secrete many substances like enzymes, resins, nectar, oils etc..


⚈ Living mechanical tissue.

⚈ Termed by Schleiden.
⚈ More or less elongated thin-walled cells but thick at corners
(thickening=pectin(mainly)+ cellulose+ Hemicellulose).
⚈ No intercellular spaces.
⚈ Generally, contain chloroplasts.
⚈ Usually present in Hydrophytes of dicot stem, leaf margins, petiole of a leaf, the pedicle of flowers etc.

⚈ Absent in woody parts of the plant [ showing secondary growth roots (except aerial roots of monestra , monocot stem].

⚈ Contain a vacuolated cytoplasm.
 Types of collenchyma

 a) Lamellar or Plate collenchyma:- cells arranged in lamellar form and have thickenings or tangential walls e.g sunflower stem.

b) Angular collenchyma:- Most common type and the deposition occurs at angles or corners of the cell wall e.g. Stem of Datura, Solanum, tomato.
 c) Lacunar or Tubular collenchyma:- Large intercellular spaces are present in this type and deposition occurs on the walls lying towards intercellular space.

 Functions of collenchyma

 ⚈ It provides mechanical support to the growing parts of the plant.

 ⚈ It also performs photosynthesis as it contains chloroplasts.
 ⚈ Being present at leaf margins prevents them from tearing.

 ⚈ Dead mechanical tissue

⚈ Termed by Mettenius.
⚈ Long, narrow thick walled lignified but without protoplast and thus dead.

⚈ Found in the hypodermis of the monocot stem.
⚈ Pits are present on lignified walls.
 Types of Sclerenchyma
 1) Sclereids:- small, extremely thick walled irregular isodiametric but their ends are not pointed. Sclereids have very narrow lumen but a number of pits.

Found in walls of nuts, pulp of Guava, Sapota (cheeku), seed coat of legumes, leaves of tea etc.

Term Sclereid was given by Tscherch

On the basis of morphology, Tscherch classified sclereid into following types
 a) Brachyscleroids or stone cells or Gritt cells:- small, spherical, roughly isodiametric sclereids found in endocarp of drup fruits, coconut,pulm etc
 b) Osteosclereids or bone cells or prop cells:- pillar like cells whose ends spread to form a bone-like structure e.g leaves of Hakea, Osmanthus, Seed coat of
 c) Macrosclereids or rod cells or Malphigi cells:- Rod-shaped sclereids found in
seed coats and sometimes induce dormancy. 
Hardest seed coat among legumes is in French Bean.
The hardest seed coat among all plants is in Lotus.
 dAsterosclereids:- star-shaped cells found in leaves of floating hydrophytes e.g  Victoria, Nelumbo, Nymphaea.
 e) Trichosclereids:- just like asterosclereids are found in floating leaves of hydrophytes but are spine like cells rather than star-shaped i.e why also
 called as internal hairs.
2) Sclerenchymatous Fibres:- Longest cells in plant body Thick walled cells with pointed ends and reduced lumen. Great tensile strength, flexibility, the elasticity of fibers enables the plant to withstand a variety of strains and tension.

Fibres contain both simple as wells as bordered pits. 

Sclerenchymatous fibres are of two types
a) Libriform fibres:- Highly thickened long fibres with simple pits and narrow lumen e.g phloem, pericycle, hypodermis fibres.
 b) Tracheidal fibres:- Thickened long fibres with simple as well as bordered pits but slightly broad lumen e.g xylem fibres.

This was all about the types and functions of permanent tissue. I hope you will like this article and don't forget to share it !...

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