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Wednesday, January 13, 2021

Plant Tissue - NEET (Botany)

Plant Tissue-NEET (Botany)

Plant Tissue
A group of cells having essentially a common function and origin is called a tissue. The plant tissue is made up of a group of cells. These cells may be either similar or dissimilar in structure, function, and origin. Plant of higher-level shows this level of cellular organization.

Fig: Plant Tissue Flowchart

Plant tissues are broadly categorized into three tissue systems. This classification is based on parts of the plants that are present.

  • Epidermis Tissue: cells formed from the outermost surface of the leaves.

  • Vascular Tissue: involved in transporting fluid and nutrients internally.
  • Ground Tissue: involved in producing nutrients by photosynthesis and preserve nutrients.

Plant tissues are grouped as two types based on their ability to divide:

A. Meristematic Tissue. 
B. Permanent Tissue.


  • It is a group of young cells, which consists of continually dividing cells and helps in the increase of length and width of the plant.
  • These are living cells with the ability to divide into the regions where they are present.
  • These are polyhedral or isodiametric in shape without intercellular spaces.
  • The cell wall is thin, elastic, mainly composed of cellulose.
  • Protoplasm is dense with a distinct nucleus at the center and vacuoles if present, are very small.
  • Cells show a high rate of metabolism.
  • It is involved in the movement of water and nutrition within the plants.
  • These tissues are responsible for both the primary and secondary growth of the plant.
  • It is the outermost tissue, functions by providing protection from mechanical injury.
  • It gives rise to the epidermis layer, cortex, endodermis, ground tissue, and vascular tissue.

Classification of Meristem:

Following criteria are used for the classification of meristems viz. origin, function, and position as follows:

A. Origin:

Primordial Meristem or Promeristem

  • It is also called an embryonic meristem.
  • It is usually occupying a very minute are at the tip of the root and shoot.

Primary Meristem

  • It originates from the primordial meristem and occurs in the plant body from the beginning, at the root and shoot apices.
  • Cells are dividing and different permanent tissues are produced from primary meristems.

Secondary Meristem

  • It develops from living permanent tissues during later stages of plant growth; hence are called secondary meristems.
  • This tissue occurs in the mature regions of the root and shoot of many plants. 

B. Position:

Apical Meristem:

  • It is produced from promeristem and forms a growing point of apices of roots, shoots, and their lateral branches.
  • It brings about an increase in the length of the plant body and is called apical initials.
  • Shoot apical meristem is terminal in position whereas in root it is subterminal i.e. located below the root cap.
  • Intercalary meristematic tissue is present in the top or base area of the node.
  • Their activity is mainly seen in monocots.
  • They are short-lived.

Lateral Meristem:

  • It is present along the sides of a central axis of organs.
  • It takes part in increasing the girth of stem or root, eg. intrafascicular cambium.
  • It is found in vascular bundles of gymnosperms and dicot angiosperms.

C. Functions:

  • The young growing root of the plant has Protoderm that forms a protective covering like epidermis around the various organs.
  • Meristem called Procambium is involved in developing primary vascular tissue while the other structures like cortex, endodermis, pericycle medullary rays, pith are formed from the region of the ground meristem. These three groups of meristem are based on the functions.
  • This is a group of cells that have lost the capacity of division and acquired permanent size, shape, and functions.
  • They are offer elasticity, flexibility, and strength to the plant.

Depending upon the types of cells, there are two types as simple and complex permanent tissues.


  • These are made up of only one type of cells carrying similar functions.
  • This tissue is either living or dead.
  • The types of simple permanent tissues: Parenchyma, Collenchyma, Sclerenchyma.

A. Parenchyma:

  • Cells in this tissue are thin-walled, isodiametric, round, oval to polygonal, or elongated in shape.
  • The cell wall is composed of cellulose.
  • The cells are living with a prominent nucleus and cytoplasm with large vacuoles.
  • This is less specialized permanent tissue.
  • The parenchyma has distinct intercellular spaces. Sometimes, cells may show a compact arrangement.
  • The cytoplasm of adjacent cells is interconnected through plasmodesmata and thus forms a continuous tissue.
  • These cells are distributed in all the parts of the plant body viz. epidermis, cortex, pericycle, pith, mesophyll cells, endosperm, xylem, and phloem.


  • The cells stores food, water, help in gaseous exchange, increase buoyancy, perform photosynthesis, and different functions in the plant body.
  • Differentiation in parenchyma cells develops vascular cambium and cork cambium at the time of secondary growth.
  • Some parenchymatous cells perform as storage chambers for starch in vegetables and fruits.

Fig: Parenchyma tissue

B. Collenchyma:
  • It is a simple permanent tissue made up of living cells.
  • The cell wall is cellulosic but shows uneven deposition of cellulose and pectin especially at corners.
  • The cell wall may show the presence of pits. 
  • The cells are similar to parenchyma containing cytoplasm, nucleus, and vacuoles but small in size and without intercellular gaps. Thus appears to be compactly packed.
  • Shape: either circular, oval, or angular in the transverse section.
  • Collenchyma is usually absent in monocots and roots of the dicot plant.


  • Collenchyma is living mechanical tissue and serves different functions in plants.
  • It gives mechanical strength to young stems and parts like the petiole of the leaf.
  • It allows bending and pulling action in plant parts and also prevents tearing of leaf.
  • Growth of organs and elongation.

Fig: Collenchyma tissue

C. Sclerenchyma:
  • It is simple permanent tissue made up of compactly arranged thick-walled dead cells.
  • The cells are living at the time of production but at maturity they become dead.
  • As cells are devoid of cytoplasm their thickened walls are due to uniform deposition of lignin.
  • The cells remain interconnected through several pits.

It is of two types: 1.) Fibers & 2.) Sclerids.

1.) Fibers

  • It is a thread-like, elongated, and narrow structures with tapering and interlocking end walls.
  • These are mostly in bundles, pits are narrow, unbranched, and oblique.
  • They provide mechanical strength.

2.) Sclerids:

  • It is usually broad, with blunt end walls.
  • These occur singly or in loose groups and their pits are deep branched and straight.
  • These are developed due to the secondary thickening of parenchyma cells and provide stiffness only.


  • This tissue functions as the main mechanical tissue.
  • It permits bending, shearing, and pulling.
  • It gives rigidity to leaves and prevents them from falling.
  • It also gives rigidity to epicarps and seeds.
  • Commercial fibers are also produced from sclerenchyma fibers. e.g. jute, flax, hemp.

  • This tissue is heterogeneous comprising more than one type of cell and all function as a single unit.
  • This tissue is involved in conducting the sap and food from source to sink area.
  • This type of complex permanent tissue: Xylem, Phloem.
Fig: Complex Permanent Tissue

A. Xylem:
  • It is dead complex tissue.
  • The xylem also provides mechanical strength to the plant body.
  • Tracheids and Vessels conduct water and minerals. These are known as hadrome = the part of the xylem mestome that conducts water and nutrients.
  • In pteridophytes and gymnosperms, tracheids are conducting elements and vessels in angiosperms, Selaginella (Pteridophyte) and Gnetum (Gymnosperm) show the presence of vessels.

1.) Tracheids:

  • It is elongated, tubular, and dead cells.
  • The ends are oblique and tapering.
  • The cell walls are uniformly thickened and dignified. This provides mechanical strength.
  • It contributes 95% of the wood in Gymnosperms and 5% in Angiosperms.
  • The different types of thickening patterns are seen on their walls such as annular (in the form of rings), spiral (in the form of spring/helix), scalariform (ladder-like), pitted is the most advanced type (small circular area) which may be simple or bordered.

2.) Vessels:

  • It is longer than tracheids with perforated or dissolved ends and formed by the union of several vessels end to end.
  • These are involved in the conduction of water and minerals.
  • Their lumen is wider than tracheids and the thickening is due to lignin and similar to tracheids.
  • In monocot, vessels are rounded.
  • In Dicot angiosperm, vessels are angular.
  • The first formed xylem vessels (protoxylem) are small and have either annular or spiral thickening.
  • The later formed xylem vessels (metaxylem) have reticulate or pitted thickenings.
  • Endarch: When protoxylem is arranged towards pith and metaxylem towards the periphery. E.g. in the stem.

  • Exarch: When metaxylem is arranged towards pith and protoxylem towards the periphery. E.g. in the roots.

Fig: Tracheids & Vessels (Xylem tissue)

3.) Xylem Parenchyma (Only living tissue):
  • The cells are small associated with tracheids and vessels.
  • This is the only living tissue among the complex tissue.
  • The function is to store food (starch) and tannins.
  • It is involved in lateral or radial conduction of water or sap.

4.) Xylem Fibers:

  • The tissue is sclerenchymatous cells and serves mainly mechanical support.
  • These are called wood fibers.
  • Shape: elongated, narrow, spindle.
  • Cells are tapering at both ends and their walls are lignified.

B. Phloem (Bast):

  • This is a living tissue. It is called as bast.
  • Phloem is responsible for the conduction of organic food material from a source (generally leaf) to a sink (other plant parts).
  • It was named leptome by Haberlandt as similar to the xylem.
  • Based on origin, it is first formed (Proto) and lately formed (Meta) phloem.
  • It is composed of sieve cells, sieve tubes, companion cells, phloem parenchyma, and phloem fibers.

1.) Sieve tubes:

  • It is a long tubular conducting channel of phloem.
  • These are placed end to end with bulging at end walls.
  • The sieve tube has a sieve plate formed by septa with small pores.
  • The sieve plates connect the protoplast of the adjacent sieve tube cells.
  • The sieve tube cell is connected to a companion cell through phloem parenchyma by plasmodesmata.
  • Sieve cells are found in the lower plants like pteridophytes and gymnosperms.
  • The cells are narrow, elongated with tapering ends and a sieve are located laterally.

2.) Companion cells:

  • This is narrow elongated and living.
  • These cells are laterally associated with sieve tube elements.
  • The companion cells have dense cytoplasm and prominent nucleus.
  • The nucleus of the companion cell regulates the functions of the sieve tube cells through simple pits.
  • From an original point of view, the sieve tube cells and companion cells are derived from the same cell.
  • The death of the one results in the death of the other type.

Fig: Sieve tubes & Companion cells

3.) Phloem Parenchyma:
  • The cells are living, elongated found associated with sieve tube and companion cells.
  • The chief function is to store food, latex, resins, mucilage, etc.
  • The cells carry out lateral conduction of food material.

4.) Phloem Fibers (only Dead tissue):

  • These are the only dead tissue among the phloem. These are sclerenchymatous. 
  • It is generally absent in the primary phloem but present in the secondary phloem.
  • These cells are with lignified walls and provide mechanical support.
  • They are used in making ropes and rough clothes.



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