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Tissue

A group of cells that are specialized to perform a particular function forms a tissue.

Tissues are mainly classified into two types:
1. Plant Tissues 2. Animal Tissues

1. Plant tissues

• Plants do not move, i.e., they are stationary.
• Most of the tissues they have are supportive, which provides them with structural strength.
• Most of these tissues are dead, as they can provide better mechanical strength than the live ones, and need less maintenance.
• Some of the plant tissues keep on dividing throughout the plant life. These tissues are localised in certain regions.

Types of Plant Tissues:

Based on the dividing capacity of the tissues, various plant tissues can be classified as growing or meristematic tissue and permanent tissue which have further sub-divisions as explained below:

Tissues
Group of cells having a common origin and similar function are termed as tissues.
A. Plant tissues: On the basis of the dividing capacity, plant tissues are of two types:

1. Meristematic tissues
2. Permanent tissues

1. Meristematic tissues: Consist of actively-dividing cells. Meristematic tissues are of three types:

• Apical meristem: Present at the growing tips of stems and roots. Important function: To increase the length of stems and roots.
• Intercalary meristem: Present at the base of leaves or internodes. Important function: For the longitudinal growth of plants.
• Lateral meristem: Present on the lateral sides of the stems and roots. Important function: To increase the thickness of stems and roots.

2. Permanent tissues: Formed from meristematic tissues, the cells in the tissue loose the ability to divider Permanent tissues are divided into two categories:

• Simple permanent tissue: Consist of only one type of cells.
  Types of simple permanent tissues:
   
• • Parenchyma: Composed of unspecialised living cells with relatively thin cell walls, intercellular space, present in soft parts of the plant. Their main function is storage.
  • Collenchyma: Composed of living and elongated cells with cell walls irregularly thickened at the comers. No intercellular space. It provides mechanical support and elasticity to plant. It helps in bending of leaves and stems.
  • Sclerenchyma: Composed of long, narrow, and thick-walled cells. This tissue is made up of dead cells and there are no intercellular spaces. Sclerenchyma cells are dead, present in seeds, nuts, the husk of a coconut, fibres of jute etc.
• Complex permanent tissue: Made up of more than one type of cells (Conducting tissues.)
  Types of complex permanent tissues:

   

  • Xylem: Conducts water and minerals from the roots to the different parts of the plant.
    Composed of four different types of cells—tracheids, vessels, xylem parenchyma and xylem fibres.
  • Phloem: Conducts food material from the leaves to the different parts of the plant.
    Composed of four different types of cells—sieve tubes, companion cells, phloem parenchyma and phloem fibres.
    Protective tissue: It is made of a single layer of cells. E.g., epidermis. The epidermis of the leaf bears stomata.