Permanent tissue: Parenchyma, Collenchyma, Sclerenchyma and their characteristics.

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  • The growth of plants occurs only in certain specific regions where the dividing tissue is present, this dividing tissue is called as Meristematic tissue.
  • TYPES: Depending on the region where they are present, meristematic tissues are classified as apical, lateral and intercalary
  • CELLS: Cells of meristematic tissue are very active, they have dense cytoplasm, thin cellulose walls and prominent nuclei. They lack vacuoles

PERMANENT TISSUE

  • The cells formed after division may take up specific role and lack the ability to divide will form permanent tissue.
  • This process of taking up a permanent shape, size, and a function is called differentiation.
  • Differentiation leads to the development of various types of permanent tissues.

SIMPLE PERMANENT TISSUE

(i) Parenchyma

  • Parenchyma is the most common simple permanent tissue.
  • It consists of relatively unspecialized cells with thin cell wall.
  • They vary in shape from spherical with many flat surfaces, to elongated, lobed, or folded.
  • They are usually loosely arranged, thus large spaces between cells (intercellular spaces) are found.
  • Present in almost all the plant, in leaves, root. flower, fruit and seed.
  • It is also associated with xylem and phloem as Xyle parenchyma and phloem parenchyma.
  • The cells can dedifferentiate to form secondary meristem.

Types of Parenchyma cells

  • Aerenchyma: In aquatic plants, large air cavities are present in parenchyma to help them float. it is called as aerenchyma. Air cavities help in gaseous exchange and to maintain buoyancy.
  • Chlorenchyma: In some situations, it contains chlorophyll and performs photosynthesis, and then it is called chlorenchyma.

(II) collenchyma

  • The flexibility in plants is due to permanent tissue called as collenchyma.
  • Bending of various parts of a plant like tendrils and stems of climbers is due to presence of chollenchyma.
  • Also found in leaf stalks below the epidermis.
  • It also provides mechanical support to stem and leaves.
  • Cells: The cells of this tissue are living, elongated and irregularly thickened at the corners. There is very little intercellular space.
  • Cell wall contains cellulose, hemicellulose, pectin, and water. It is plastic in nature means deformed when pressure is applied and reformed again.
  • Cells may develop extra thickening at places like angles. intercellular spaces and tangential walls, on the basis of that they are of following types:
  • In lacunate types the intercellular spaces are present and the walls are thick at corners and creating small cavities called lacunae
  • In lamellar type the thickening is deposit on tangential walls, cells arranged in alternating rows.
  • In angular type thickening are localized at angles of cell wall.

(iii) Sclerenchyma.

  • It is the tissue which makes the plant hard and stiff.
  • The cells of this tissue are dead. They are long and narrow.
  • It provides strength to the plant parts.
  • The walls are thickened due to lignin. Often these walls are so thick that there is no internal space inside the cell.
  • Cell wall is uniformly thick.
  • This tissue is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts.
  • Fibers and sclerids are types of sclerenchyma cells.





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