Plant tissue | its classifications | their definition

-   Plant tissue 

             Plant tissue is composed of different types of tissue, like meristematic tissue, vascular tissues, etc. Unlike animal, plant body is abundant in dead supportive tissues. Plant are adapted for a sedimentary existence as they do not move. Because of this reason, the main requirement is structural support which can be provided by dead tissues which can be provided by dead tissues with least maintenance. 

     In plant body, the growth is not uniform, that is, their growth is confined to particular region. Plant tissue according to their dividing abilities can be divided in two group :- 

    1:- Meristematic tissue

    2:- Permanent tissue

1:- Meristematic tissue

          The plant tissue that can be divided throughout it's life is called meristematic tissue. Meristematic tissue again can be divided according to their position as three parts:-

      a) Apical Meristem:- seen at growing tip of roots and shoots, and help in increasing lenght of root and stem. 

      b) Intercalary Meristem :- it occurs between mature tissues. In grasses, it is responsible for the regeneration of part eaten by grazing herbivores. 

      c) Lateral Meristem :- it is responsible for increase in girth of the plant body. 

-   Permanent Tissue 

          The tissue that do not undergo division are called permanent tissue. Meristematic tissue loses its ability to divide and takes up a permanent shape, size and function. This process is called differentiation. Thus, meristematic tissue undergoes differentiation to form permanent tissue. 

        Depending on whether they are made up of one type of cell or different types of cells, permanent tissue can be divided into two :

1:- Simple Permanent tissue

2:- Complex permanent tissue

   1:- Simple permanent tissue:- simple permanent tissue is made up of only one type of cell. Simple permanent tissue are of different types listed as follows. 

     a)- Parenchyma 

     b)- Collenchyma

     c)- Sclerenchyma

    a:- Parenchyma :- they are living tissues. The cells of parenchyma can be spherical, oval, polygonal or elongated. Parenchymatous cells have a thin cell wall and dense cytoplasm. They are involved in a variety of function, like photosynthesis, gaseous exchange, food storage and other specialized functions. 

     b:- Collenchyma :- Collenchyma tissue consists of living cells. Their cell wall is irregularly thickened at the corners. Their cells can be oval, spherical or polygonal. They give mechanical support and flexibility to the plants. They allow the plants to bend without breaking. 

    c:- Sclerenchyma :- Sclerenchyma are dead tissue. Their cells are. Long with narrow lumen. Their wall is thick due to lignin deposition. Sclerenchyma provides mechanical support to the organs. It is in the fruit walls of nut, seed coats of legume, etc., for example, in coconut husk. 

  2:- Complex Permanent tissue :- 

            Permanent tissue that is made of more than one type of cell is called complex permanent tissue. There are two different types of complex permanent tissues: 

  1:- xylem 

  2:-phloem. 

     1:- Xylem :-  Xylem is involved in the transport of water and mineral nutrients that are absorbed through roots from the soil. It also provides mechanical support to the plant. 

Xylem is composed of four different elements as listed below. 

     a:- Xylem tracheids - main conducting elements. 

     b:- Phloem vessels - main conducting elements. 

     c:- Xylem Parenchyma - storage tissue and helps in lateral conduction of water. 

     d:- Xylem fibres - provide support to the plant 

      

     2:- Phloem :- Phloem tissues help in the transport of photosynthesis products to various parts of the plant body. Phloem tissue is made up of four different types of elements. 

        a:- sieve tubes - sieve tube elements are long tube-like and are placed end to end. 

        b:- companion cells - companion cells are seen associated with the sieve tube elements. 

        c:- Xylem Parenchyma :- it's function mainly in storage. 

        d:- phloem fibres - it provide mechanical strength. 

 -  Epidermal Tissue :- 

            It forms the outermost covering of the plant body. It consists of compactly arranged cells. It is usually found as single continuous layer. Epidermal Surface is coated with thick waxy later called cuticle, which prevents water loss. The specialized openings present on the epidermis are called stomata. Stomata are enclosed by a pair of kidney- shaped cells called guard cells. Gaurd cells regulate the openings and closing of stomata. Transpiration (loss of water in the form of water vapour) and gaseous exchange takes place through stomata. 

     

 

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