Tissues, Organs, Organ System, Organism | Part 1
Tissue can be defined as a group of cells more or less alike in size, shape, performing the same function and having common origin.
Histology :- The microscopic study of tissues and their functions is known as histology.
Plants body are made up of different kinds of tissues these are classified into two groups are
(I) Meristematic tissues
These are present only at the growing regions like shoot tip, root tip and Cambium (region which is responsible for growth in thickness)
These cells divide continuously thus helping in increasing the length and the growth of the plant.
Characteristics of meristematic tissue
(1) They are living cell; compactly arranged without intercellular spaces.
(2) They are thin walled are may be round oval, polygonal or rectangular. in shape.
(3) The vacuoles are few and smaller in size.
(4) They have dense granular cytoplasm.
(5) The nucleus is large and conspicuous.
(6) The cells are immature and undifferentiated.
(7) The plastids are in preplastid stage.
(8) They are capable of dividing indefinitely.
(9) They don’t store reserve food material.
(10) They are Usually found in the apices of root and shoot.
Type of meristems
According to their position in the plant body, meristems are divided into three Categories:-
(1) Apical meristem:- It is present at the growing tips of the stems and roots and increases the length of the stem and the root.
(2) Lateral meristem (Labium): The girth of the stem or root increases due to this meristem.
(3) Intercalary maristem :- It is present at the base of the leaves or internodes
Permanent tissues are derived from meristematic tissues till they lose the ability to divide.
They have the definite shape, and size
They may be living or dead, and thin or thick walled.
The cells are large having vacuolated cytoplasm.
Simple permanent tissues
The common simple permanent tissues are-
(c) Scleren Chyma
Parenchyma :- (Living)
It is widely distributed in plants body like stem roots, leaves, flowers and fruits.
The parenchymatous cell are isodiametric
They may be oval, round, polygonal, or elongated and have thin walls.
Functions of Parenchymatous tissue
It store and assimilate food.
It provide mechanical strength.
It Stores waste products such as tannin, gum, crystals, resins of inorganic waste etc.
(b) Collenchyma (Living)
These cell are present below the epidermis
It consist of thin walled cells, which are much thickened at the corners where number of cells joint together. The thickening is due to a deposition of cellulose and pectin at the corners.
Intercellular spaces are absent
It may be circular, oval or polygonal
Main Functions of collenchyma
They provides the mechanical support and elasticity to the plants.
They manufacture sugar and starch when they contain chloroplasts.
The cell of this type of tissue are long, narrow, thick and lignified.
The length of the sclerenchyma cells varies. From 1 mm to 550 mm in different plants.
It also provides mechanical support to the plants.
Some times specials types of sclerenchyma cell called “Sclereids” develop in various parts of the plant, such as cortex, pith, phloem & hard seeds –etc.
(ii) Protective Tissue
These tissue are usually present in the outermost layer of the plant body such as leaves, flowers, stem and roots.
This layer is one cell thick and is covered with cutin, and protect the inner tissues present in the plant body.
The walls of these cells are heavily thickened by the deposition of suberin which help in prevention of loss of water.
It is used for insulation, shock absorbers, linoleum and sport good.
This layer contain the small opening called pores or stomata which helps in transpiration and exchange of gases.
(iii)Complex permanent tissues
Complex tissues are made up of more than one type of cells and work together as a unit
Complex tissues are to two types-
This conducting tissue is composed of cells. i.e., elements of four different Kinds-tracheids, Vessels or tracheas, Xylem parenchyma and xylem sclerenchyma
These carry water and mineral salts upward from the root to different parts of the shoot.
It is composed of tour elements are sieve tubes companion cells, phloem parenchyma and phloem fibres.
In this tissue, sieve tubes have perforated walls, which helps in translocation (distribution of the prepared food).