Tissues

3 Simple Permanent Tissues

  • Simple permanent tissues are composed of cells which are structurally and functionally similar.
  • These tissues are made up of one type of cells.
  • A few layers of cells beneath the epidermis are generally simple permanent tissue.
  • Simple Permanent tissues are divided into two types.
    • Supporting tissues
    • Protective tissues

Supporting Tissues:

Supporting tissues are further divided into three parts:

  • Parenchyma
  • Collenchyma
  • Sclerenchyma

Parenchyma:

Parenchyma forms the bulk the plant body. Parenchyma cells are living and possess the power of division.
Structure:

  • They consist of relatively unspecialized cells.
  • The cell wall is thin and encloses dense cytoplasma.
  • They are living cells. In other words, parenchyma cells have living protoplasm.
  • They have loosely packed cells.
  • They have large spaces between cells.
  • The parenchymatous cells are oval, round, polygonal or elongated in shape.
  • They surround a large central vacuole.

Occurrence:

  • The parenchyma is widely distributed in plant bodies such as stem, toots, leaves flowers and fruits.

Functions:

  • Parenchyma generally stores and assimilates food.
  • Parenchyma is called chlorenchyma when it contains chlorophyll and performs photosynthesis
  • In aquatic plants, large air cavities are present in parenchyma to help them float. Such a parenchyma type is called aerenchyma.
  • Parenchyma servers as a packing tissue, to fill the spaces between other tissues.
  • Parenchyma acts as a primary support to the stem.
  • Transport of materials occurs through cells or cell walls of parenchyma cells.
  • Parenchyma cells are metabolically active; their intercellular air spaces allow gaseous exchange.
  • Parenchymatous tissue stores waste products of plants such as tannin, gum, crystals, resins or inorganic waste, etc.
  • In xerophytes i.e. arid plants and succulents i.e. plants having fleshy parts, parenchyma acts as a water storage issue.

Collenchyma:

Tissue also consists of living cells is characterized by the deposition of extra cellulose at the corners of the cells.
Structure:

  • The cells of this tissue are living.
  • They are elongated and irregularly thickened at the corner.
  • There is very little intercellular space in collenchyma.

Occurrence:

  • The cells of collenchyma are located below the epidermis.

Functions:

  • Chollenchyma gives flexibility to plants
  • It allows bending of various parts of a plant like tendrils and stems of climbers without breaking.
  • It also provides mechanical support.

Differences between Parenchyma and Collenchyma:

Parenchyma Collenchyma
The tissue consists of thin-walled living cells. The tissue consists of cells having localised thickening in their cell walls.
It is distributed in almost all the parts of the plant body.

It occurs mostly in the aerial parts of the plants and is restricted to the other layers.

The living cells of parenchyma assimilate and store food. They also store waste products. Collenchyma is the chief mechanical tissue in parts of a young plant particularly in the young dicotyledonous stems.

Sclerenchyma:

Sclerenchyma cells are dead cells and they are devoid of protoplasm.

Structure:

  • The cell walls of sclerenchyma are greatly thickened of lignin.
  • It is this tissue which makes the plant hard and stiff.
  • The cells of sclerenchyma are closely packed without intercellular spaces.
  • They are dead cells. Thus, these cells are fitted together like tiles in a mosaic floor.
  • Cells of sclerenchyma are of two types – Fibres and sclereids.
  • Fibres consist of very long, narrow, thick and lignified cells.
  • Fibres are usually pointed at both ends and are clustered into strands.
  • In contrast to fibres, sclereids (also called grit cells or stone cells) are irregular-shaped.

Occurrence:

  • They are found in stems, roots, veins of leaves, hard coverings of seeds and nuts.
  • Husk of coconut is made of sclerenchymatous tissue. It yields coir, a well-known fibre used for mats, cordage, brushes, etc.

Functions:

  • It provides strength to the plant parts.

Comparison between Collenchyma and Sclerenchyma:

Collenchyma Sclerenchyma
It consists of living cells. It consists of dead cells.
It cells contain cytoplasm.

It cells are empty.

Its cell walls are cellulosic. Its cell walls are lignified.
The thickening of cell wall is not uniform. Cell wall thickening is uniform.
Lumen of the cell is wide. Lumen of the cell is narrow.
It provides mechanical support and elasticity to the plant body. It is chiefly mechanical tissue.

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