question_answer

  Name the tissue responsible for flexibility in plants. How would you differentiate it from other permanent tissues? Or Describe structure and function of different types of epithelial tissues.

Answer:

  The tissue responsible for flexibility in plants is collenchyma. The distinction of collenchyma from other permanent tissues is given below

S. No.	Parenchyma	Collenchyma	Sclerenchyma
(i)	It consists of relatively unspecialized cells with thin walls. The cells of this tissue are living.	The cells of this tissue are living, elongated and irregularly thickened at the corners.	The cells of this tissue are dead. They are long and narrow as the walls are thickened due to lignin (a chemical substance which acts as cement and hardens them).
(ii)	The cells in this tissue contain large intercellular spaces.	There is very little intercellular space.	The walls of cells are so thick that there is no internal space inside the cell and between the cells.
(iii)	It provides support to plants and also stores food.	It allows easy bending in various parts of a plant (leaf, stem) without breaking. It also provides mechanical support to plants.	It provides strength to the plant parts.

Or The epithelial tissue are classified as follows (i) Squamous epithelium It consists of extremely thin and flat cells forming a delicate lining, e.g., the esophagus and lining of mouth. Skin epithelial cells arranged in many layers to prevent wear and tear, they are arranged in a pattern of layers, the epithelium called as stratified squamous epithelium.                          (1) (ii) Cuboidal epithelium Cells are cube-like with rounded nuclei and form lining of kidney tubule and duct of salivary glands, where it provides mechanical support. It also helps in absorption, excretion and secretion.                                                                                         (1) (iii) Columnar epithelium It consists of tall cells, which are pillar-like having elongated nuclei. It is found in inner lining of intestine and helps in absorption and secretion.                                                                                               (1) (iv) Ciliated columnar epithelium The ciliated columnar epithelium tissue contains cilia in respiratory tract. The sec ilia move and their movement pushes the mucus forward to clear it. This type of epithelium is thus ciliated columnar epithelium.                                                                                                                                                     (1) (v) Glandular epithelium Some-times epithelial cells acquire additional specializations as gland cells, which can secrete substances at epithelial surface. A portion of epithelial tissue folds in ward and multicellular gland is formed called glandular epithelium.                                                                                                                        (1)