Plnt tissues

Plnt tissues

• 2.
  Tissue is acellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function.
• 3.
  The study oftissue is known as histology or, in connection with disease, histopathology.
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  Plant Tissues Permanent Tissues Meristimatic Tissues (Cells with speciallised structure and function that have lost their (These cells continuously divide throughout the life of the plant) ability to divide further) Simple Permanent Tissue Apical Meristem Complex Permanent Tissue Parenchyma Xylem Lateral Meristem Collenchyma Phloem Intercalary Meristem Sclerenchyma
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  Meristematic tissue: Cellsof this tissue continue to divide throughout the life of the plant. Some of these cells lose their ability to divide and become part of other tissues. Name of the Location Function tissue Apical Meristem Present at the growing tip of stem Increase in length of stem and root and root Lateral Meristem Found on the lateral sides of Increase in girth of stem (also called roots and stem and root cambium) Intercalary Present at the base of leaves or Growth of leaves and Meristem internodes branches
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  A longitudinal sectionthrough a growing shoot tip showing apical meristematic tissue. Note that the cells are small, have dense cytoplasm, and are very tightly packed.
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  High power viewof a longitudinal section of the Coleus apical meristem. The apical meristem is a dome-shaped mass of dividing cells at the tip of the shoot. The apical meristem will produce the three primary meristems: protoderm, procambium, and ground meristem. These three meristems in turn will produce new cells that will differentiate into the epidermis, primary vascular tissues, and ground tissues (pith and cortex).
• 9.
  A longitudinal sectionthrough a root tip. The meristematic tissue is located just above the root cap. This too is apical meristem; division of these cells followed by cell elongation results in the root growing in length.
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  It is across section of a dicot stem. Focus on the two large vascular bundles in the center of the slide. The xylem tissue is stained red. Just above the xylem is a layer of meristematic tissue, the vascular cambium. The phloem tissue is found outside of the vascular cambium.
• 11.
  This is ahigh-power view of a cross-section showing a lateral meristem, the vascular cambium, in the same plant shown in previous slide. Again, the xylem tissue is stained red, and the large cells on the top of the slide are phloem. The green brick-like cells between the xylem and phloem is the area in which the vascular cambium is located. The new cells produced by the cambium are initially like those of the cambium itself, but, as they grow and mature, their characteristics slowly change as they differentiate into other tissues. The vascular cambium is a single layer of cells within this brick like region; it is responsible for the growth in diameter of a stem. The tissues produced by the vascular cambium are secondary tissues.
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  Permanent tissue: Cellsof this tissue have lost their ability to divide and they have a specialized structure to perform specific functions. Based on the type of cells present in the tissue, the Permanent tissue is divided into two categories: Simple Permanent Tissue and Complex Permanent Tissue. While the simple permanent tissue consist of only one type of cells (eg. Parenchyma), the complex permanent tissue consists of more than one type of cells (eg. Xylem and phloem)
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  S i mp l e P e r m a n e n t T i s s u e s Parenchyma Structure:It is the fundamental tissue composed of thin walled, living cells whose cell wall is composed of cellulose. Small intercellular spaces are present between the cells. Location and function: It occurs in all soft parts of plants and is meant for storage of food and to provide turgidity to softer parts of plants. Parenchyma tissue in stem and roots store nutrients and water. Types of parenchyma: i) Chlorenchyma :Certain parenchymatous tissue contain chloroplast and synthesize food by the process of photosynthesis. ii) Aerenchyma: In aquatic plants parenchymatous cells have air cavities between them to store air, such a tissue is called Aerenchyma. It provides buoyancy to the aquatic plants so that they can float in water.
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  Collenchyma Structure: This tissueis composed of somewhat elongated cells with cell walls that are irregularly thickened at corners due to deposition of cellulose or pectin. They may be oval, circular or polygonal. Very little intercellular spaces are present. Location: It occurs below the epidermis of stem and petiole (stalk of the leaf) and around veins. Function: This tissue provides mechanical support and flexibility and in some cases it may possess chloroplasts to perform Photosynthesis. The stem and leaves are able to bend easily and then come back to their original position due to the presence of collenchyma.
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  Collenchyma in TransverseSection Showing Wall Thickenings 1. Cell Wall 2. Wall Thickenings 3. Protoplasm 4. Vacuole
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  Sclerenchyma Structure: It isa tissue of dead and thick walled cells, having no intercellular spaces. The thickenings are of cellulose or lignin or both. Several unlignified areas called pits often develop on walls. Location: This tissue is usually found in the hard and stiff parts of the plant like seed coat, husk of coconut, in the stem around vascular bundles, veins of leaves and hard covering of fruits and nuts. Function: It is the chief mechanical tissue in plants and is able to bear push, pull, strain and shearing forces. It provides strength to plant parts and also protects the delicate parts of the plants. They are of two types: fibres and sclereids.
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  Sclerenchyma
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  Epidermis and Bark The protective tissues The epidermis usually consists of a single-layered group of cells that covers plants leaves, flowers, roots and stems. It forms a boundary between the plant and the external world. Bark is formed from the meristem that appears later in the life cycle of a plant. Woody stems and some other stem structures produce a secondary covering called the secondary meristem or periderm or cork cambium that replaces the epidermis as the protective covering. The periderm replaces the epidermis, and acts as a protective covering like the epidermis. Cells produced on the outside by periderm form the cork. Cells of have suberin in their walls to protect the stem from drying and pathogen attack. Older cork cells are dead, as is the case with woody stems. As the stem grows, the cork cambium produces new layers of cork which are impermeable to gases and water.
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  A high-power viewof one glandular hair. Secretory hairs may provide a chemical defense against insects.
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  Another type ofsurface tissue, the outer bark or periderm (stained red in this slide). Periderm is found on the surface of woody plants; it includes the cork cells on the surface of older woody stems. The periderm replaces the epidermis in plants that have secondary growth. The cork cells are dead; it is their waterproofed cell walls that function as the protective outer covering of plants. Meristematic cells within the periderm (cork cambium, the other lateral meristem) produce the cork cells.
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  Complex Permanent Tissues Xylemand Phloem
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  Xylem It is acomplex permanent tissue, which is specialized for the conduction of water and mineral substances in the plant body. Xylem is a heterogenous tissue made up of four different types of cellular elements. They are: •Xylem tracheids •Xylem tracheae or vessels •Xylem fibers and •Xylem parenchyma
• 29.
  Phloem: Phloem is acomplex permanent tissue, which is specialized for the conduction of food and other organic substances. Phloem is also a heterogenous tissue, made up of four different types of cellular elements, namely, •Sieve tubes •Companion cells •Phloem parenchyma and •Phloem fibres