Tissue

Tissue



During the development of a multicellular organism, cells differentiate so that they can carry out different functions. Differentiation is the process by which a cell becomes a specialised type of cell.

Definition of PlantTissue

 A plant tissue can be defined as a cell or a group of cells dividing, to give rise to large number of cell, which is collectively referred as tissues. They are structurally and functionally similar to these cells.

Plant Tissue Systems

Plants do have a higher level of structure called plant tissue systems. A plant tissue system can be defined as a functional unit, which connects all organs of a plant. Like animal tissue system, plant tissue system is also grouped into various tissues based on their functions. 

Types of Plant Tissue Systems

There are three types of tissue systems.

Dermal Tissue

• They are the tissues, which covers the external part of the herbaceous plants.
• They are composed of epidermal cells, which secrete the waxy cuticle.
• Waxy cuticles are responsible for protecting plants against water loss.
• Dermal tissue consists of Epidermis and periderm. 

Epidermis

• They are the outermost layer of the primary plant body, which covers roots, stems, leaves, floral parts, fruits and seeds.
• They are one layer thick with cuticle.
• They are composed mostly of unspecialized cells- parenchyma and sclerenchyma.
• They include trichomes, stomata, buIIiform ceIIs, etc.

Periderm

• They are the outermost layer of stems and roots of woody plants such as trees. They are also called as barks.
• They replace epidermis in plants that undergo secondary growth.
• They are multilayered structures.
• They include cork cells, which are nonliving cells that cover the outside of stems and roots. 
• The periderm protects the plant from injuries, pathogens and also from excessive water loss.

Ground Tissue

• They synthesize the organic compounds and support the plants by storing the produced products.
• They are composed  of  parenchyma cells and also include collenchyma and sclerenchyma cells. 

Parenchyma

• They are the general cells of plants, which are circular in shape and have very thin wall.
• They are present in all plant cells.
• They have very large vacuoles and are frequently found in all roots, stem, leaves and in fruits
• Parenchyma cells help in synthesizing and storage of synthesized food products.
• Parenchyma cells also controls plant's metabolism like photosynthesis, respiration, protein synthesis.
• They also play a vital role in wound healing and regeneration of plants.

Collenchyma

• Collenchymas are a specialized parenchyma tissue, which are found in all green parts.
• Collenchyma cells are elongated with unevenly   thickened walls.
• They are alive during the cell maturity.
• Collenchyma cells controls the functions of young plants.
•  A collenchyma cell provides a support to plants by not restraining growth, which is caused due to their absence of secondary walls and hardening agent in their primary walls. 

Sclerenchyma

• They are rigid, non-living cells.
• They have thick, lignified secondary walls and lack protoplasts at maturity.
• They provide strength 
• A sclerenchyma cell also provides a support to plants with the help of hardening agent present in their cells.

Sclerenchyma cells are of two types:

• Sclereids: They are short, irregular in shape and have thick, lignified secondary walls
• Fibers: They are long, slender and are arranged in threads.

Vascular Tissues

• They are specialized cells with transport of water, hormone and minerals throughout the plant.
• They contain transfer cells, fibers in addition to xylem, phloem, parenchyma, cambium and other conducting cells.
• They are located in the veins of the Leaves.

Xylem

• The term “Xylem” is derived from the Greek word meaning “Wood”.
• They are dead with hollow cells, which consist of only cell wall.
• They play a vital role in transporting water and dissolved nutrients from the roots to all parts of a plant.
• They transport the nutrients in the upward direction .i.e. from the root to the stem, leaves and flower.
• Xylem is also called as water-conducting cells.

Phloem

• The term “phloem” is derived from the Greek word meaning “Bark”.
• They are live cells, which lack nucleus and other organelles.
• They transports dissolved organic food materials (sugars) from the leaves to all parts of a plant.
• They transport the nutrients in the downward direction .i.e. from the leaves to the different parts of the plant.
• Phloem is also called as sugar-conducting cells.

Types of Plant Tissue

There are two types of tissue systems.

Meristematic tissue


Meristematic tissues are group of cells, which have the ability to divide. This tissue consists of small, cubodial densely packed cells, which keeps on dividing to form new cells. These tissues are capable of stretching, enlarging and differentiate into other types of tissues as they mature. Meristematic tissues give rise to permanent tissues.

General characteristics of Meristematic tissues

• They have very small cells with thin cell walls.
• Their cells have large nuclei.
• Their cells have very small vacuoles and they lack intercellular spaces.
• They remain young forever and divide actively throughout the life of the plant.
• In plants, these tissues are found in the -Tips of roots, stems, nodes of stems, buds, in between the xylem and phloem, under the epidermis of dicotyledonous plants and also producing branch roots.

Kinds of Meristematic tissues

• Apical meristems : They are found at the tip of stems and roots. During the cell division, this meristem helps in cellular enlargement and also it influence the shapes of the mature plants.

• Lateral meristems : They are found along the sides of roots and stems .They play a vital role in increasing the width or diameter of stems and roots. 

• Intercallary meristems : They are found at the bases of young leaves and internodes. They are mainly responsible for further lengthening of stems and leaves.

Plant Tissue Functions

Different types of plant tissue have their own respective functions.

• The plant tissue helps in providing mechanical strength to both the internal and external organs.
• They also help in rendering the elasticity and flexibility to the organs. 
• The tissue also helps in easy bending in various parts of a plant like- leaf, stem and branches without causing any damages to main plant.
• The tissue also helps transportation of materials thorough out the plants and prevents water loss.
• They divide to produce new growth and build the mass of the plants.
• They are involved in various cellular metabolisms like photosynthesis, regeneration, respiration, etc