TISSUE

Tissues

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

Plant tissue culture is a practice used to develop plant under sterile laboratory conditions, often to produce clones of a plant. The production of exact copies of plants that produce particularly good flowers, fruits, or have other desirable traits.

Advantages of Tissue Culture

• To quickly produce mature plants.

• The production of multiples of plants in the absence of seeds or necessary pollinators to produce seeds.

• The regeneration of whole plants from plant cells that have been genetically modified.

• The production of plants in sterile containers that allows them to be moved with greatly reduced chances of transmitting diseases, pests, and pathogens.

• The production of plants from seeds that otherwise have very low chances of germinating and growing, i.e.: orchids and nepenthes.

• To clean particular plant of viral and other infections and to quickly multiply these plants as 'cleaned stock' for horticulture and agriculture.

Types of Plant Tissues

1) MERISTEMATIC TISSUE

Meristematic tissue is growth tissue and the location of most cell division. It is known as undifferentiated tissue because cells in the meristematic tissue will eventually become vascular, ground, or dermal tissue.

Plants generally grow where meristematic tissue is present. At the tips of roots and stems, the meristematic tissue is called the apical meristem.

Primary Growth: The primary growth of the plant occurs in the apical meristem. The growth in length of a plant part is due to primary growth.

Secondary Growth: Lateral growth or growth in thickness in a plant is called secondary growth, which occurs in lateral meristem tissue. Woody trees and shrubs display secondary growth when the plants become enlarged and thickened.

2) PERMANENT TISSUE

When the cells formed by meristematic tissue take up a specific role and lose the ability to divide. As a result, they form a permanent tissue. This process of taking up a permanent shape, size, and a function is called differentiation. Cells of meristematic tissue differentiate to form different types of permanent tissue.

Simple permanent tissues

These tissues are called simple because they are composed of similar types of cells which have common origin and function. They are further classified into:

(I) Parenchyma

(II) Collenchyma

(III) Sclerenchyma

1. Parenchyma: Parenchyma is Greek word where "parn" means besides and "enchien" means to pour. Parenchyma is the most specialized primitive tissue. It mainly consist of thin-walled cells which have intermolecular spaces between them. The cell wall is made up of cellulose. Each parenchymatous cell is iso-diametric, spherical, or oval in shape. It is widely distributed in various plant organs like root, stem, leaf, flowers and fruits. They mainly occur in cortex epidermis, piths and mesophyll of leaves.

Function of Parenchyma: The main function of parenchymatous tissue is assimilation and storage of reserve food materials like starch, fats and proteins. They also store waste products such as gums, resins, and inorganic waste materials.

2. Collenchyma: Collenchyma is Greek word where "Collen" means gum and "enchyma" means infusion. It is a living tissue of primary body like Parenchyma. Cells are thin-walled but possess thickening of cellulose and pectin substances at the corners where number of cells join together. This tissue gives a tensile strength to the plant and the cells are compactly arranged and do not have intermolecular spaces. It occurs chiefly in hypodermis of stems and leaves. It is absent in monocots and in roots.

Functions of Collenchyma: Collenchymatous tissue acts as a supporting tissue in stems of young plants. It provides mechanical support, elasticity, and tensile strength to the plant body. It helps in manufacturing sugar and storing it as starch. It is present in margin of leaves and resists tearing effect of the wind.

3. Sclerenchyma: Sclerenchyma is Greek word where "Sclrenes" means hard and "enchyma" means infusion. This tissue consists of thick-walled, dead cells. These cells have hard and extremely thick secondary walls due to uniform distribution of ligin. Lignin deposition is so thick that the cell walls become strong, rigid and impermeable to water. Sclerenchymatous cells are closely packed without intra-cellular spaces between them. Thus, they appear as hexagonal net in transverse section. The cells are cemented with the help of lamella. The middle lamella is a wall that lies between adjacent cells. Sclerenchymatous cells mainly occur in hypodermis, pricycle, secondary xylem and phloem. They also occur in endocorp of almond and coconut. It is made of pectin, lignin, protein.

Types of Sclerenchyma

Fibres- Fibres are long, elongated sclerenchyamtous cells with pointed ends.

Sclerides- Sclerenchymatous cells which are short and possess extremely thick, lamellated, lignified walls with long singular piths. They are called sclerides.

Function of Sclerenchyma: The main function of Sclerenchymatous tissues is to give support to the plant.

2. 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. These tissues are concerned with transportation of water, mineral, nutrients and organic substances. The important complex tissues in vascular plants are xylem, phloem.

Xylem: Xylem is a chief, conducting tissue of vascular plants. It is responsible for conduction of water and inorganic solutes.

Tracheids- Trachids are elongated, tube-like dead cells with elongated end-walls. End walls remain intact and possess piths. In transverse section, they usually occur as polygonal cells and lignified walls.

Vessels - Vessels are placed one upon another. Their end walls are perforated. They form long tubes or channels for conduction of water and minerals.

Xylem Parenchyma - Xylem Parenchymatous cells are living cells present in xylem. They help in lateral conduction of organic solutes and storage reserves. 4. Xylem Fibres - Xylem Fibres are lignified fibres present in xylem which provide mechanical strength to the plant body.

Xylem is a major conducting tissue of vascular plants. It serves in upward movement of water and minerals from root to different parts of plant.

2. Phloem: Phloem is a chief conducting tissue of vascular plants. It is regarded as a living tissue responsible for translocation of organic solutes.

a. Sieve tube - Sieve tubes are long tubular structures composed of elongated sieve tube elements placed one above other forming a continuous tube.

b. Companion cell - Companion cells are living cells always associated with sieve tubes. Sieve tube elements and companion cells arrive from the same, initial cell and therefore forms a single functional unit. Each companion cell shows presence of fine piths with all the living components of the cell.

c. Phloem Parenchyma - These cells are living parenchymatous cells that are present in phloem. These cells help in storage of food.

d. Phloem Fibres - Phloem fibres are formed by dead, sclerenchymatous fibres.

The main function of phloem is 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 large number of sieve pores.

Animal Tissues

Based on morphology, animal tissues can be grouped into four basic types. Multiple tissue types comprise organs and body structures. While all animals can generally be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism.

1. Connective tissue

2. Muscle Tissue

3. Nervous Tisuue

4. Epithilial Tissue

Connective Tissue: Connective tissue is comprised of cells separated by non-living material, which is called extra cellular matrix. As the name suggests connective tissues are meant to make connections. Connective tissue holds other tissues together such as in the formation of organs, and has the ability to stretch and contract passively. Bone, often referred to as osseous tissue, and blood are examples of specialized connective tissues.

Muscle Tissue: Muscle cells form the active contractile tissue of the body known as muscle tissue. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs.

Types of Muscles

1.Smooth Muscle or Visceral Muscle found in inner linings of organs.

2.Skeletal Muscle is attached to bone to provide movement.

3.Cardiac Muscle is in heart and makes possible the pumping action of the heart.

Nervous Tissue: Cells comprising the central nervous system and peripheral nervous system are classified as neural tissue. In the central nervous system, neural tissue forms the brain, cranial nerves and spinal cord and, in the peripheral nervous system, peripheral nerves inclusive of the motor neurons. You can imagine the nervous tissue like an electrical wiring in which the brain is the power generator, the spinal cord is the main line and peipheral nerves are lines going to different organs.

Epithilial Tissue: Epithelial tissues are formed by layers of cells that cover organ surfaces such as the surface of the skin, the airways, and the inner lining of the digestive tract. The cells comprising an epithelial layer are linked via semi-permeable, tight junctions.

Functions of Epithelial Tissues: Protection of internal organs in case of intestine, kidney and heart and protection of external organs also. In fact skin is an epithelial tissue covering the body. Skin is the first line of defence against foreign substances. A burn victim doesn’t die because of burn but because the whole defensive layer of skin is broken exposing the body to various infections.