Permanent Tissue

Tissues that have become mature and do not have the ability to divide further are called permanent tissues. Permanent tissues are made up of cells that do not undergo cell division. The cells in these tissues are modified to perform some specific functions. The cells in permanent tissues are fully grown, bigger in size, and have a certain shape. The metabolic rate is lower in the cells of permanent tissues. Permanent tissues are derived from the meristematic tissue.

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Types of Permanent Tissue

Depending upon their structure, origin, and function permanent tissues are of 3 types.

• Simple Permanent Tissue

• Complex Permanent Tissue

• Secretory Tissues

Simple Permanent Tissue

Simple permanent tissues are made up of cells from the same origin, which have similar structures and functions. They are also called homogeneous tissues and they are further classified into three types.

Parenchyma

Parenchyma is the kind of simple permanent tissue found all through the plant body. These tissues are made up of living cells with thin cell walls which are loosely packed to accommodate the intracellular space. The cells of parenchyma permanent tissue are generally round or oval in shape. Parenchyma consists of chlorophyll, that’s why it takes part in photosynthesis. It also has storage functions as well as other functions. The cell wall of the parenchyma is made up of cellulose and consists of vacuoles and a nucleus.

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Collenchyma

Collenchyma is also a living tissue consisting of a thick cell wall that is made up of cellulose, water, and pectin. The cells are compactly packed in collenchyma tissues causing very little intracellular space. The refractive index of collenchyma tissue is the highest due to the presence of pectin. It contains less amount of chlorophyll. It is mainly found in the hypodermis of the leaves and stems of dicots. It is not found in the roots of plants and neither in the monocots. 

Functions of Collenchyma Tissue-

The functions of these tissues are to provide mechanical strength, elasticity, and tensile strength to the plant body. It also participates in the sugar manufacturing within the plant body and stores it in the form of starch. It is also found in the leaf margins to prevent the leaf from tearing by the wind. It provides flexibility and undergoes dedifferentiation to form phellogen or cork cambium and regain meristematic activity.

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Types of Collenchyma

There are 4 types of collenchyma, these are briefly explained below.

• Tangential Collenchyma- Plate collenchyma and lamellar collenchyma are other names for them. They are organised in rows and have thicker tangential walls. The Clerodendron stem is one example. 

• Lacunar Collenchyma- The characteristic of this kind of tissue is the presence of intercellular gaps in this form of collenchyma. Thickening is particularly prominent in this form of collenchymatous cell near intercellular gaps. Examples of this type include Malva stems, Salvia petioles, and so on.

• Angular Collenchyma- Collenchyma of this sort is the most prevalent. The walls of this form of collenchyma cell thicken only at the angles or at the corners. They lack intercellular gaps and have a circular lumen. Cucurbita is a common example.

• Annular Collenchyma- These are characterised by the presence of the uniform thickening of the cell walls with heavy deposits of pectin and hemicellulose in walls.

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Sclerenchyma

Sclerenchyma tissue is composed of dead cells that have a thick cell wall with negligible protoplasm. The secondary cell wall of these tissues is very thick and secretes lignin, which provides mechanical support to the plants. There is a complete absence of intramolecular space between the cells. Due to thick and rigid outer cell walls consisting of lignin, it is impermeable to water.

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Types of Sclerenchyma Tissue:

Fibers and sclereids are the two basic forms of sclerenchyma, they are briefly described below.

Fibres-

Fibres are long, elongated cells found in stems, roots, and the vascular bundles of leaves. The bundle caps and sheaths of vascular bundles, especially in monocotyledonous plants, are made up of fibers with tapered ends and can be several centimeters long. In higher plants, they are the longest cells. They can range in size from 1 to 8 mm in length.

They're frequently seen in clusters, clumps, or patches. They lack a nucleus and cytoplasm. The cell walls of fibers are evenly thickened and lignified. Intraxylary and extraxylary fibres are the two primary kinds of fibres. The xylem contains intraxylary fibres. Outside of the xylem, extraxylary fibers can be found in the cortex, pericycle, or phloem.

Sclereids-

Sclereids may be found in a variety of plant tissues, including the periderm, cortex, pith, xylem, phloem, leaves, and fruits, and come in a variety of forms like spherical, oval, or cylindrical. This kind of cell is responsible for the hardness of nuts' shells, the coats of many seeds, and the stone of drupes (cherries and plums). They are frequently characterised by thicker cell walls. Sclereids are rigid and stiff, with very tiny cavities. Plant organs rely on them for structural and mechanical support.

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Complex Permanent Tissue

Complex permanent tissues are a collection of structurally different cells working together as a unit performing various complex functions. Thus, complex tissues consist of cells that are not of one type.  Complex permanent tissues are also called vascular tissues because they help the transportation of water, minerals, and organic matter throughout the plant body. The two most common complex permanent tissues found in plants are Xylem and Phloem.

Xylem

Xylem is also known as wood tissue. Xylem tissues are responsible for the conduction of minerals and water from roots to leaves of the plant. It also provides physical support to the plants. Xylem tissues are made up of parenchyma cells, fibres, vessels, and tracheid cells. The tracheid and vessels are long, elongated, and hollow.

Phloem

The phloem of the bust plant tissue is another type of vascular tissue found in plants. Its main function is the translocation of food from leaves to different plant parts. Phloem tissue consists of a sieve tube, companion cell, phloem fibre, and phloem parenchyma. Apart from the translocation of food, they are also responsible for the transportation of proteins and mRNAs throughout the plant body.

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Secretory Tissues

Tissues that are related to the secretion of gums, raisins, volatile substances, nectar, latex, etc. are called secretory tissue. Two types of secretory tissue are found in plants.

• Laticiferous Tissues- These tissues are elongated, thick-walled, and multinucleated and consist of a milky or yellowish pigment called latex. They are spread over the mass of parenchyma cells in plants.

• Glandular Tissues- The tissues which consist of glands are glandular tissues. These glands contain either secretory or excretory products. Internal glandular tissues secrete various essential things in various plants like essential oils, mucilage (in betel leaf), gum, resin, tannin, digestive enzymes, etc.

External glandular tissues are mostly hairs that secrete water, or gum-like substances like tobacco, honey in carnivorous plants, and poisonous substances in some plants. Example- Common Nettle.

Where are Permanent Tissues Found?

Permanent tissues are found in all mature plants. Depending upon their structure and site of origin, they carry out various important functions within the plant body. Simple permanent tissues are found below the epidermis of the plant, spread around in layers of cells. Parenchyma is found in the cortex of the stem and roots and in the mesophyll of leaves. Collenchyma is found in the leaf stalk and leaf midribs below the epidermis. Sclerenchyma is found in stems, around the vascular bundle, around the hard covering of seeds and nuts, and in veins of leaves. Complex tissue xylem is found throughout the plant body, the centre of the vascular bundle and phloem is found outside the vascular bundle, in leaf veinlets and in the innermost layers of the bark of old trees.

Based on structural and functional similarities, tissues are organized into four categories.  These categories are epithelial, connective, muscle, and nervous.   The primary tissue types work together to contribute to the overall health and maintenance of the human body. So any disruption in the structure of tissue can lead to injury or disease.

These tissues are made up of specialized cells which are grouped together to perform various important functions in the body. 

Muscle Tissue

Muscle Tissues are elastic with stimulation receptors so that they can stimulate the contraction of muscles and help with movement. There are three types of muscle tissue found in the human body- Cardiac muscle tissue, Smooth muscle tissues, and Skeletal muscle tissue.

Epithelial Tissue

Epithelial Tissues create a protective layer and cover the exterior surface of the body.  Internal cavities and passageways form certain glands. It consists of sensory receptors and is involved in the diffusion of ions and molecules. 

Connective Tissue

Connective Tissue, as the name suggests binds all the cells and organs of the body and provides protection and support to different body parts. It is found between other tissues across the body.

Nervous Tissue

Nervous tissue is a tissue of the nervous system. It is composed of neurons and all of them show the presence of an axon. Axon is the part of the cell. A bunch of axons constitutes the nerves in the tracts in the central nervous system and the peripheral nervous system. As nervous tissue surrounds the nerves, spinal cord, and the brain, its primary functions are to receive stimuli and send impulses to the brain and spinal cord.

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What is Bone Tissue?

Bone tissue is a connective tissue found in the membrane of the bones. It is hard so that it can provide rigidity to the bones. Bone tissue is also called osseous tissue. The bone tissue has two types of the matrix material. The first type which is made up of collagen and elastic fibers provides strength and flexibility. The second type is made up of minerals, salts, calcium and therefore it is hard. Adequate proportions of both kinds of matrix material in the bone tissue provide them the needed flexibility and rigidity.

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