Tissue 9th Class Full Chapter Detailed Explaination

We know that unicellular organism, beings compose of just a single cell, perform all life activities in the same cell. There is no division of labour. Opposite to this, in multicellular organisms, the small cell does not perform all activities of the organisms, the same cell does not perform all activities of the organisms. In other words, all cells do not perform the same functions. Instead, there is a division of labour. Different cells of the organisms become specialised to perform a particular type of function. This process is called differentiation.

In multicellular organisms, the differentiated cells form several types of groups. The group of cells, which are similar in structure and origin, that work together to perform a particular function, forms a tissue. So a tissue can be defined as a group/ cluster of cells, which are similar in origin, structure and function. Muscles, blood, nerve, xylem, phloem etc. are all examples of tissue.

Plant and Animal Cells are not Similar

Plant Tissues are different from animal tissues. These differences have been shown in the following table.

Plant Tissues Animal Tissues
  • Plant Tissues are Stationary of fixed
  •  Some of the animal tissues such as blood and lymph are able to move from one place to another
  • Most of the Plant Tissues are dead. Living tissues are very few
  •  Most of the animal tissues are living
  • Plant Tissues mainly provide strength and rigidity
  •  Animal Tissues perform various functions and therefore they are flexible and movable. Some tissues like bones and cartilage provides strength and rigidity
  • The living tissues in plants (meristems) divide throughout their life. These tissues are localised to some specific areas. So, there is clear cut demarcations between the dividing and non-dividing regions
  •  Animal Tissus have limited division capacity. Moreover, they are Scattered throughout the body. So, there is no demarcation between dividing and non-dividing regions.
  • Tissues structures is comparatively simple and less organised
  • Tissue structure is very complex, Specilised, and more organised.

 

Plants and animals have different feeding methods. locomotion, different ways of responding to environmental stimuli. These fundamental differences in the modes of life of these two major groups of organisms make them different at the level of tissues also.

Plant Tissues

Plant contains various types of tissue. These are mainly of two types: 

  1. Meristematic Tissues
  2. Permanent Tissues

Meristematic Tissues (MERISTEMS)

Growth of plant is not uniform. Some tissues have power of division, while other do not divide at all. The tissues which have power of division are known as meristematic tissues

A meristematic tissue consists of a group of cells which remain in active and continuous state of division and they retain their power of division. Important features of these tissue are

  • They are composed of living and very active cells.
  • Usually intercellular spaces are absent.
  • Cells are oval, rounded or polygonal in shape.
  • Cells have thin cellulose walls and prominent nuclei.
  • Cells are rich in cytoplasm with small/ no vacuoles. (The Vacuoles are small/ absent because the function of these cells is to divide only i.e., not to store the materials)
  • These cells have great power of division, They help the plant to growth in length and girth (diameter). Almost all other types of tissues are derived from meristems.

Location

Meristematic Tissues are located mainly in the apical regions (Root tip and Shoot Tip). Besides, these are also present in the intermediate regions (intercalary) and also in the cambium of vascular bundles.

Permanent Tissues

Different parts of the plants have to perform different vital functions. So, the cells formed by meristematic tissues, lose their ability to divide and take up specific roles. Such cells give rise to permanent tissues. So, permanent tissues are formed by the differentiation of meristematic tissues.

Permanent tissue are those tissues, in which the growth and division capacity has been stopped (lost) temporarily or permanently. These are, therefore, not important from a growth point of view.

The process of taking up a permanent shape, size, and a specific function by the cells is called differentiation. Differentiation causes specialisation of cells.

Important Characters of Permanent Tissues

  • These tissues may be living or dead
  • These may be thin or thick-walled. The thin-walled tissues are usually living while those with thick walls, are usually dead.
  • The cells have a fixed shape.
  • The living cells have no or very poor division capacity.
  • Intercellular spaces are often present.

Protective Tissues

These Tissues are mainly present in the outer peripheral regions of root, stem, leaves, and flower Etc. and serve to provide protection to underlying tissues. Important protective tissues are: (a) Epidermis, (b) Cork.

(A) Epidermis

  • It is the outermost layer of plant organs. It is usually single-cell thick. The epidermis forms continuos layers of the aerial parts of the plant.
  • Epidermis provides protection to internal tissues.
  • Epidermis of roots contains many hair like stem is green and protective in nature. But in older stem it gets ruptured due to increase in the thickness of the plant.
  • In plant which are found under dry climate, the epidermis becomes very thick to prevent water loss.
  • Epidermal cells on the serial parts of the plants secrete a shiny, waxy layer, which is also resistant to water. This also prevents the water loss, mechanical injury and invasion by fungal parasites
  • The epidermis of the leaves in not continuous. It is perforated by very small apertures, called stomata. Each stoma consists of two kidney-shaped guard cells. These cells together enclose on aperture in the middle, called stomatal aperture. Guard cells are surrounded by many accessory cells
  • Through Stomata, exchange of gases between the atmosphere and leaves takes place. Besides, stomata are also involved in transpiration (removal of waters in the form of vapours from leaves). For extra protection, epidermis is covered with cutin/ cuticle (thick waterproof, waxy coating).

(B) Cork

It is formed by the activity of lateral meristems in older stems. Cork is a protective tissue, it is very light and highly compressible. It does not catch fire easily.

Cork cells have a chemical, called suberin. This makes the cork impervious (impermeable) to gase and water

Cork serves to protect the underlying woody tissues. Commercially, cork is used for insulation. It is waterproof. It is also used as a shockabsorber.

 

 

Leave a Comment