Plant Tissues

The tissue is a group of cells. The cells in a tissue can be similar or different. The groups of cells thus formed carry specific functions. A group of different tissues makes an organ.

There are two types of tissues :

(i) Plant Tissue; and

(ii) Animal Tissue. 

Here we try to get a hold of what are the different type of plant tissues.

PLANT TISSUES

Plant tissues are further divided into Meristematic Tissues and Permanent Tissues.

1. Meristematic Tissue
Meristematic tissue is growth tissue and the location of cell division. It is known as an undifferentiated tissue because in the meristematic tissue will eventually become vascular, ground, or dermal tissue.  Meristematic tissue is classified on the basis of the regions, where they are present.

(i) Apical Meristem
These are present at growing tips of stems and roots. Thus, are helpful in increasing the length of the stems and the roots. It acts as pro-meristem having actively dividing cells, giving rise to other meristems.

(ii)  Intercalary Meristem
These are present at the base of the leaves or internodes (on either side of the node) of twigs.  It helps in longitudinal growth (elongation) of plants.

(iii)  Lateral Meristem (Cambium) ·
These are present on the lateral sides of stems and roots.  It helps in increasing the girth of stem and root.

1_Apical Meristem
Meristematic Tissue

2. Permanent Tissue
This tissue is formed from the cells of meristematic tissue when they lose their ability to divide and have attained a permanent shape, size and function by the process called differentiation.   As a result of differentiation, the meristematic tissues tend to form different types of permanent tissues are as follows: 

(i) Simple Permanent Tissue
It is made up of only one type of cells, i.e. the cells forming these tissues are similar in structure and function.  The simple permanent tissue is further classified as: 

(a) Parenchyma
A few layers of cells form the basic packing tissue. They are present in cortex and pith of stems and roots in the mesophyll of leaves.

Characteristics:
(i) These are simple living cells with little specialisation and thin cell wall.
(ii) Cells are usually loosely packed with large spaces between them  (intercellular spaces).

Functions:
(i) It serves as food storage tissue.
(ii) This tissue provides support to plants.
(iii) When the parenchyma cell contains chlorophyll in some situations, it performs photosynthesis. Such type of parenchyma tissue is called chlorenchyma.
(iv) In aquatic plants, large air cavities are present in parenchyma cells in order to give buoyancy to plants, wh1ch help them to float. Such type of parenchyma tissue is called aerenchyma.
(v) The parenchyma of stems and roots also stores nutrients and water.

parenchyma
Parenchyma (i) transverse section,
parenchyma 2
Parenchyma (ii) longitudinal section

(b) Collenchyma
These tissues are generally found in leaf stalks below the epidermis and leaf midribs.

Characteristics
(i) Cells are living, elongated and irregularly thickened at the corners due to the deposition of pectin.
(ii) They have very little intercellular spaces.

Functions:
(i) It provides mechanical support and elasticity (flexibility) to plants.
(ii) It also allows easy bending in various parts of a plant (leaf and stem) without breaking.

Collenchyma
Collenchyma (i) transverse section,
Collenchyma_t
Collenchyma (ii) longitudinal section;

(c) Sclerenchyma
This type of tissue is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts.

Characteristics:
(i) The cells of the sclerenchymatous tissue are dead.
(ii) The cells are long and narrow in appearance.
(iii) Cell walls are thickened due to lignin  (a chemical substance) deposition, which acts as cement and hardens them.
(iv) Due to the presence of thick walls, there is no internal space between the cells.

Function:
(i) It is known to be the chief mechanical tissue, which makes plant hard and stiff, e.g. husk of coconut is made up of sclerenchymatous tissue.
(ii) It forms a protective covering around seeds and nuts.  It gives rigidity, flexibility and elasticity to plant body.

Sclerenchyma
Sclerenchyma

(ii)Complex Permanent Tissue
A complex permanent tissue may be classified as a group of more than one type of tissue having a common origin and working together as a unit to perform a function. Types of complex permanent tissue are:

(a) Xylem

(b) Phloem

(a) Xylem
It is responsible for the transport of water and minerals from roots to other parts of the plant.  The cells of xylem have thick walls and many of them are dead. Xylem consists of various types of elements,    which are as follows:

I. Tracheids
(i) These are dead, long, tubular structures with a tapering end.
(ii) They transport water and minerals vertically.

II. Vessels
(i) Long, tube-like structures, formed by a row of cells, placed end to end.
(ii) These are also dead cells with lignified walls.
(iii) They also help in the conduction of water.

III.  Xylem Parenchyma
(i) Xylem Parenchymatous cells are living cells present in xylem.
(ii) The lateral conduction of organic solutes and storage reserves.

IV. Xylem Fibres
(i) Xylem Fibres are liquefied fibres present in xylem which provide strength to the plant body.
(ii) Xylem is a major conducting tissue of vascular plants. It serves the upward movement of water and minerals from root to different parts of the plant.

Xylem
Xylem

(b) Phloem
Phloem is a chief conducting tissue of vascular plants. The main function of phloem is a translocation of organic solutes from the leaves to the storage organ and later from the storage organ to the growing part. Sieve tube allows free diffusion of soluble, organic substances across sieve plates due to the presence of a large number of sieve pores.

Phloem is made up of the following four types of elements:

I. Sieve tubes
(i) These are tubular cells with perforated walls.
(ii) They have a thin layer of cytoplasm.

II. Companion cells
(i) These are small elongated cells having thin walls which are not perforated and have active cytoplasm.
(ii) They help sieve tubes in translocation of food.

III. Phloem Fibres
(i) They are thick walled sclerenchyma cells which provide mechanical strength to the tissue.

IV. Phloem Parenchyma
(i) They are thin-walled cells which help in storage and slow lateral conduction of food.

Phloem
Phloem
Difference Meristematic and Permanent
Difference between Meristematic Tissue & Permanent Tissue
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