What is Parenchyma,Collenchyma and Sclerenchyma?State their functions.
Answers
Simple tissues are a collection of similar cells that perform a common function. These tissues are of 3 types.
Epithelial Tissue - OpenStax CNX
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Epithelial Tissue - OpenStax CNX
(a) Parenchyma (b) Collenchyma (c) Sclerenchyma.
3 Types
Parenchyma
In parenchymatous tissue all cells are isodiametric and thin walled. The cells may be oval, circular or polygonal with intercellular spaces. They are living. This tissue is present in all organs of the plant e.g., roots, stems, leaves, flowers, fruits and seeds.
Functions ;
The main function of this tissue is storage of food.
2. In fleshy stems and Fig. 15.8 Parenchyma. leaves parenchyma cells function as water storage tissue e.g., Opuntia, ^Euphorbia,
3. In hydrophytes large air cavities are formed in between cells of these tissues, which are filled with air. This types of parenchymatous tissue is called aerenchyma. The plants become buoyant due to the presence of air and also gaseous exchange is facilitated.
4. Some times in parenchymatous cells develop chloroplasts. Such parenchyma is called chlo-renchyma and such cells participate in photosynthesis.
5. Some times such cells start to divide e.g., Cork cambium root cambium, and help the plant in secondary growth, formation of cork and healing of wounds.
Collenchyma
Collenchymatous cells are longer than parenchyma cell.. They are living. The intercellular spaces in this tissue are absent because in intercellular spaces at the corner of cells thickenings of cellulose and pectin develop due to which the cell wall become rigid and thick at corners. Sometimes collenchyma develops chloroplasts. Collenchyma is usually found as 3-4 layered hypodermis of herbaceous dicotyledonous stem. They are absent in monocot stems.
Functions :
1. It provides mechanical support to the organs and due to its peripheral position in stems it resists bending and pulling action of wind.
2. When chloroplasts are present it takes part in photosynthesis.
Sclerenchyma
This tissue differ from previous tissues in possessing thickened secondary walls which may or may not be lignified. They are of various shapes and sizes when mature. They are dead. They are of two types :
1. Sclerenchymatous fibres 2. Stone cells
These are discussed in detail.
1. Sclerenchymatous fibres :
Fully developed fibres are long and tapering at the ends. In some cases the cellwall becomes so much lignified that the lumen is greatly reduced.Wall has small circular pits. The normal length of fibres is 1-3 mm but in jute and Boehmeria their length may be from 20-550 mm.
The fibres are present in hypodermis of monocot stem,in pericycle of many dicots, in secondary wood, in vascular bundle sheath in monocot stems and hypodermis of many leaves.
The main function of sclerenchyma is mechanical strength.
2. Stone cells (Sclereids) :
They are lignified, extremely thick walled so that the lumen of the cells is almost oblitrated and may be spherical,oval,cylindrical,T- shaped and even stellate. They are generally found in hard parts of the plant e.g. endocarp of walnut and coconut. They form part of seedcoat in some members of leguminoseae.
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➧ Types 0f Simple Permanent Tissues are:-▬▬▬▬▬▬▬▬▬▬▬▬▬⤵
❶❭ Parenchyma:-┅┅┉┅┅┉┅┅┉┅┅┉┅┅┉┅☟
● The unspecialised living plant tissue formed of thin walled rounded cell.
● This cell are isodiametric & least specialised.
● It is considered at the fundamental tissue or ground tissue.
➧ It's Characteristics are:-━━━━━━━━━━━━━━━━━━☟
❱ Cells are living cells with thin cell wall of cellulose.
❱ They are rounded, oval or polygonal in shape with intercellular spaces.
❱ Cytoplasm is dense with one large or more than one small vehicles.
➧ It's Functions are:-━━━━━━━━━━━━━━━━━━☟
❱ It form the ground tissue or packing tissue in plants.
❱ It provide rigidity to the plant by keeping cell rigid.
❱ It's cell store food.
❱ It helps in wound healing, regeneration & grafting.
❱ It cells are allow to exchange of respiratory gases.
❷❭ Collenchyma:- ┅┅┉┅┅┉┅┅┉┅┅┉┅┅┉┅☟
● It is found in steam leaf, leaf stalk & leave midribs of dicot herbaceous plant.
● It forms a layer below the epidermis called hypodermis.
● It is absent in monocot stem.
➧ It's Characteristics are:-━━━━━━━━━━━━━━━━━━☟
❱ Cells are living unfairly elongated.
❱ They appear polygonal, 0val or circular in cross-section.
❱ Cells surrounded by thik primary cell wall alone.
❱ The cell wall is thickened along the corner due to the deposition of cellulose & pectin.
❱ The cytoplasm has a large central vacuole.
➧ It's Functions are:-━━━━━━━━━━━━━━━━━━☟
❱ It provide mechanical support to the delicate developing organs of herbaceous Dicot stem.
❱ It cells combine both tensile strength & flexibility.
❱ It cells with chloroplast carrying out photosynthesis.
❱ This cell also store food & allow growth & elongation of 0rgan.
❸❭ Scelerenchyma :- ┅┅┉┅┅┉┅┅┉┅┅┉┅┅┉┅☟
● It is a hard supporting tissue formed of long, narrow & pointed ends.
● It occurs in root stem, leaves & petiole.
● These cells are dead with thick lignified walls that gradually lose Protoplasm.
➧ It's Characteristics are:-━━━━━━━━━━━━━━━━━━☟
❱ These are dead cell without nucleus & cytoplasm.
❱ Their cell wall is formed of cellulose & hemi-cellulose.
❱ It is thickened due to the secondary the position of Lignin.
❱ Lignin act as a cement & hardens the cell wall.
❱ The lignified cell wall has pits.
➧ It's Functions are:-━━━━━━━━━━━━━━━━━━☟
❱ It provide most of the support in a plant.
❱ To compressive & tensile stresses in plants.
❱ It allows the organs to withstand bending, shearing & compression.
❱ It's cells provide protective, vascular & supportive functions.
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