2. Tissue is a cellular 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 of tissue is known as histology or, in connection with disease, histopathology.
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6. Meristematic tissue: Cells of 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.
8. Alongitudinal section through a growing shoot tip showing apical meristematic tissue. Note that the cells are small, have dense cytoplasm, and are very tightly packed.
9. High power view of 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).
10. Zone of Cell elongation Apical Meristem Root cap A longitudinal section through 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.
11. It is a cross section of a dicotstem. 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.
12. This is a high-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.
13. Permanent tissue: Cells of 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)
14. Simple Permanent Tissues ParenchymaStructure: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.
16. Collenchyma Structure: This tissue is 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.
18. Sclerenchyma Structure: It is a 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.
22. 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.
27. BARK Another type of surface 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.
36. Multicellular (large) organisms function more efficiently if cells become specialized for specific functions. There are four types of tissues found in animals: epithelial, connective, nerve, and muscle tissue. Sponges do not have tissues.
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40. Epithelial tissue Epithelial tissue covers the whole surface of the body. It is made up of cells that are closely packed and are composed of one or more layers. This tissue is specialised to form the covering or lining of all internal and external body surfaces. Epithelial tissue that occurs on surfaces on the interior of the body is known as endothelium. Cellular arrangements in epithelial tissues. (a) Squamous. (b) Cuboidal. (c) Columnar. (d) Stratified squamous. (e) Pseudostratified. (f) Transitional.
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44. extracellular matrixExtracellular matrix is a special feature that distinguishes connective tissue from the other tissues of the body. This matrix may be jelly-like, fluid, dense or rigid. The nature of matrix differs according to the function of that particular connective tissue.
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47. Muscular tissue Muscles of the body are made up of elongated muscle cells also known as muscle fibre. The movement of the body is brought about by the contraction and relaxation of contractile protein present in muscle cells. These contractile proteins are actin and myosin.
52. Nervous Tissue All living cells have the ability to react to stimuli. Nervous tissue is specialisedto react to stimuli and to conduct impulses to various organs in the body which bring about a response to the stimulus. Nerve tissue (as in the brain, spinal cord and peripheral nerves that branch throughout the body) are all made up of specialised nerve cells called neurons.
53. Neurons have many different shapes and sizes. However, a typical neuron in a human consists of four major regions: a cell body, dendrites, an axon, and synaptic terminals. Like all cells, the entire neuron is surrounded by a cell membrane. The cell body is the enlarged portion of a neuron that most closely resembles other cells. It contains the nucleus and other organelles (for example, the mitochondria and endoplasmic reticulum). The dendrites and axon are thin cytoplasmic extensions of the neuron. The dendrites, which branch out in treelike fashion from the cell body, are specialized to receive signals and transmit them toward the cell body. The single long axon carries signals away from the cell body. In humans, a single axon may be as long as 1 meter (about 3 feet). Some neurons that have cell bodies in the spinal cord have axons that extend all the way down to the toes.
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55. A nerve is an enclosed, cable-like bundle of axons (the long, slender projections of neurons). A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons.
