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

 

• 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.