Plant Tissues

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Plant Tissues

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   A plant tissue is defined as a group of similar cell to perform similar function and exhibit similar properties for example photosynthesis, transport etc.

Classification of Plant Tissues:

There are two major categories of tissues in plants i.e. Meristematic tissues and Permanent tissues.

Meristematic Tissues:

Definition:

   A meristematic tissue is the plant tissue that has the ability to divide actively throughout its life.

Location:

   They are found at the tips (apex) and sides of roots, shoots and stem.

Salient Features:

  •  These tissues are connected to cells, which have the ability to divide.
  •  The cells are thin walled, have large nucleus and number of small vacuoles.
  •  Usually they do not have intercellular spaces, so the cells are arranged compactly.

Types:

   These are two main types of meristematic tissues in plants.

  •  Apical meristematic.
  •  Lateral meristematic.

Apical Meristematic:

  •  Apical meristematic tissues are present at the apex of roots and stems.
  •  According to their position they are apical meristematic.
  •  Stem and root increase in length by the division of cells of these tissues, This type of growth is called primary growth.

Lateral Meristematic:

  •  Lateral meristematic are located on the lateral sides of roots and shoots.
  •  Lateral meristematic are responsible for increase in girth (breadth or thickness) of plant parts. This growth is called secondary growth.

Permanent Tissues:

Definition:

   Plant tissue that has completed its growth and differentiation and is usually incapable of meristematic activity.

Origin:

They originate from primary meristem.

Salient Features:

  •  The cells of these tissues do not have the ability to divide.
  •  They may have intercellular spaces in between cells.
  •  They have differentiated cells to carry out specific functions.

Types of Permanent Tissues:

There are two types of permanent tissues.

  •  Simple permanent tissue.
  •  Complex or compound tissue.

Simple Permanent Tissue:

   The simple tissue is made up of one type of cell forming a uniform or homogeneous system of cells.

Types of Simple Permanent Tissue:

   Simple tissues may be further divided into following types.

  •  Epidermal tissue.
  •  Ground tissue.
  •  Supporting tissue.

Epidermal Tissue:

   The tissue which forms the outer protective covering of the plant and is represented , in the primary plant body, by epidermis is called dermal (epidermal) tissue.

Features:

  •  Epidermal tissues are composed of a single layer of cells.
  •  They cover the plant body.

Functions:

  •  They act as a barrier between the environment and internal plant tissues.
  •  In roots, they are also responsible for the absorption of water and minerals.
  •  On stem and leaves they secrete cutin (the coating of cutin is called cuticle) which prevents evaporation.
  •  Epidermal tissues also have some specialized structures that perform specific functions; for example root hairs and stomata.

Ground Tissue:

Definition:

A ground tissue arises from the ground meristem, If fills in the soft parts of the plants, such as cortex, pith, pericycle, etc.

Salient Features:

  •  These tissues are made up of parenchyma cells.
  •  They are spherical but flat at point of contact.
  •  They have a thin primary cell wall.
  •  They have large vacuoles for storage of food.
  •  In leaves, they are known as mesophyll.

Functions:

  •  They primary function is the storage of food.
  •  They are also responsible for photosynthesis.
  •  These tissues also provide structural support to plants.

Supporting Tissues:

Definition:

   The tissues which provide strength, flexibility and structural support to plants are called supporting tissues.

Functions:

   They provide structural support and rigidity to the plant.

Types:

   They are further classified into two types.

  •  Collenchyma.
  •  Sclerenchyma.

Collenchyma:

   Collenchyma is a tissue composed of living elongated cells having unevenly thickened primary cell walls.

There are two major categories of tissues in plants i.e. Meristematic tissues and Permanent tissues.

Location:

   They are mostly found in cortex of young stems, midribs of leaves and in petals of flowers.

Function:

   These tissues provide structural support to plants without rejecting growth due to their relatively soft cell wall.

Sclerenchyma:

   The sclerenchyma consists of thick and rigid secondary cell walls, often unified.

Location:

   They are often found in xylem and hard fruit coats etc.

Salient Features:

  •  It consists of dead cells.
  •  The cell walls are lignified.

Compound or Complex Tissue:

Definition:

   A plant tissue composed of more than one type of cell is called a compound or complex tissue.

Examples or Types of Compound Tissues:

   Xylem and phloem tissues, found only in vascular plants, are examples of composed tissues.

  •  Xylem.
  •  Phloem.

Xylem:

Definition:

   The tissue that functions to transport water and minerals from roots to aerial parts is called xylem.

Location:

   In dicot they are located inside the phloem.

Salient Feature:

Due to the presence of lignin, the secondary walls of its cells are thick and rigid with overlapping ends.

Structure:

   It is composed of the following elements.

  •  Tracheid’s are non-living, long, narrow and thin cells with tapered ends.
  •  Vessels are non-living, short, wide and stacked end forming a tube like structure with perforated walls.

Functions:

  •  They perform the function of transport of water and minerals from roots to aerial parts of plants. (Ascent of sap)
  •  They also provide structural support to the plant.

Phloem:

Definition:

   The tissue that transports nutrients from leaves to various parts of plant is calledphloem. Phloem is a complex, food conducting tissue in vascular plants.

Location:

   In dicot they are located outside the xylem.

Structure:

Phloem is composed of four elements:

  •  Sieve tubes are elongated living cells with perforated end walls, which do not possess nucleus and are main conducting cells.
  •  Companion cells which are closely associated with sieve tubes and control the sieve tubes.
  •  Phloem parenchyma which is mainly concerned with storage of organic matter, tannins etc.
  •  Phloem fibers are elongated cells with lignified walls.

Functions:

   They transport food and other metabolic products from leaves to various parts of the plant.

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