Tissue is a cellular organizationallevel intermediate between cells anda complete organism. Hence, a tissueis an ensemble of cells, not necessarilyidentical, but from the sameorigin, that together carry out aspecific function.
The study of tissue isknown as histology or, inconnection withdisease, histopathology.
Plant tissues Animal TissuesSince plants are stationary so they Since animals are mobile so theydo not require much energy, Hence require more energy, hence moremore living tissues are not required. living tissues are required.In plants, most tissues provide Animals move from one place tostructural strength. Most of these another in search of food, sheltertissues are dead etc., hence they need more energy9can provide mechanical strength as and there more tissues are living.easily as the living ones and needless maintenance.Growth is limited to certain regions Cell growth is uniformally distributedStructural organisation of organs is Structural organisation of organs andcomparatively less complex. organ systems is more specialised and complex.
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
Meristematic tissue: Cells of this tissue continue to dividethroughout the life of the plant. Some of these cells lose theirability 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
A longitudinal section through a growing shoot tip showing apical meristematic tissue. Note that the cells are small, have dense cytoplasm, and are very tightly packed.
High power view of a longitudinal section of the Coleus apicalmeristem. The apical meristem is adome-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 threemeristems in turn will produce newcells that will differentiate into the epidermis, primary vascular tissues, and ground tissues (pith and cortex).
A longitudinal section through a root tip. The meristematic tissue islocated just above the root cap. This too is apical meristem; divisionof these cells followed by cell elongation results in the root growing in length.
It is a cross section of a dicotstem.Focus on the two largevascular bundles in the centerof the slide.The xylem tissue is stainedred.Just above the xylem is alayer of meristematictissue, the vascular cambium.The phloem tissue is foundoutside of the vascularcambium.
This is a high-power view of a cross-section showing a lateral meristem, the vascular cambium, in thesame 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.
Permanent tissue: Cells of this tissue have lost their ability todivide and they have a specialized structure to performspecific functions.Based on the type of cells present in the tissue, thePermanent tissue is divided into two categories:Simple Permanent TissueandComplex Permanent Tissue.While the simple permanent tissue consist of only one typeof cells (eg. Parenchyma),the complex permanent tissue consists of more than onetype of cells (eg. Xylem and phloem)
S i m p l e P e r m a n e n t T i s s u e sParenchymaStructure:It is the fundamental tissue composed of thin walled, livingcells whose cell wall is composed of cellulose. Small intercellular spacesare present between the cells.Location and function: It occurs in all soft parts of plants and ismeant 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 chloroplastand synthesize food by the process of photosynthesis.ii) Aerenchyma: In aquatic plants parenchymatous cells have air cavitiesbetween them to store air, such a tissue is called Aerenchyma. It providesbuoyancy to the aquatic plants so that they can float in water.
CollenchymaStructure: This tissue is composed of somewhat elongated cells withcell walls that are irregularly thickened at corners due to deposition ofcellulose or pectin. They may be oval, circular or polygonal. Very littleintercellular spaces are present.Location: It occurs below the epidermis of stem and petiole (stalk ofthe leaf) and around veins.Function: This tissue provides mechanical support and flexibility andin some cases it may possess chloroplasts to perform Photosynthesis.The stem and leaves are able to bend easily and then come back totheir original position due to the presence of collenchyma.
SclerenchymaStructure: It is a tissue of dead and thick walled cells, having nointercellular 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 theplant like seed coat, husk of coconut, in the stem around vascularbundles, veins of leaves and hard covering of fruits and nuts.Function: It is the chief mechanical tissue in plants and is able to bearpush, pull, strain and shearing forces. It provides strength to plantparts and also protects the delicate parts of the plants.They are of two types: fibres and sclereids.
Epidermis and Bark The protective tissuesThe epidermis usually consists of a single-layered group of cells that coversplants leaves, flowers, roots and stems. It forms a boundary between the plantand 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 coveringcalled the secondary meristem or periderm or cork cambium that replaces theepidermis as the protective covering.The periderm replaces the epidermis, and acts as a protective covering like theepidermis.Cells produced on the outside by periderm form the cork. Cells of have suberinin their walls to protect the stem from drying and pathogen attack. Older corkcells are dead, as is the case with woody stems. As the stem grows, the corkcambium produces new layers of cork which are impermeable to gases andwater.
A high-power view of one glandular hair. Secretory hairs may provide a chemical defense against insects.
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 thesurface 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.
XylemIt is a complex permanenttissue, which is specializedfor the conduction of waterand mineral substances inthe plant body. Xylem is aheterogenous tissue madeup of four different types ofcellular elements.They are:•Xylem tracheids•Xylem tracheae or vessels•Xylem fibers and•Xylem parenchyma
Phloem:Phloem is a complexpermanent tissue, which isspecialized for theconduction of food andother organic substances.Phloem is also aheterogenous tissue, madeup of four different types ofcellular elements, namely,•Sieve tubes•Companion cells•Phloem parenchyma and•Phloem fibres
Multicellular (large) organisms function more efficiently ifcells 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.
Epithelial tissueEpithelial tissue covers thewhole surface of the body. It ismade up of cells that areclosely packed and arecomposed of one or morelayers. This tissue isspecialised to form thecovering or lining of all internaland external body surfaces.Epithelial tissue that occurs onsurfaces on the interior of thebody is known asendothelium. Cellular arrangements in epithelial tissues. (a) Squamous. (b) Cuboidal. (c) Columnar. (d) Stratified squamous. (e) Pseudostratified. (f) Transitional.
Types of Epithelial Tissue Name of Structure Location Functionthe TissueSimple Squamous cells have the appearance of thin, flat They form the lining of cavities such Protection and transportation ofSquamous plates.The nucleus is flat and elliptical. as the mouth, oesophagus, blood substances through a selectivelyEpithelium vessels, heart and lungs permeable surface.Simple Cells are arranged in many layers and the top layers of The mammalian skin is an example of Protection and to prevent wearStratified this tissue may consist of dead cells that are covered dry, keratinised, stratified and tearEpithelium with keratin (a protein) epithelium.Cuboidal cuboidal cells are roughly square or cuboidal in shape. Cuboidal epithelium is found in Protection and mechanical supportEpithelium Each cell has a spherical nucleus in the centre glands and in the lining of the kidney tubules as well as in the ducts of the glands. They also constitute the germinal epithelium which produces the egg cells in the female ovary and the sperm cells in the male testes.Columnar Cells occur in one or more layers. The cells are elongated and Columnar epithelium forms the lining Protection, absorption of food (inEpithelium column-shaped. The nuclei are elongated and are usually of the stomach and intestines. Some small intestine), secretion of located near the base of the cells. columnar cells are specialised for enzymes sensory reception such as in the nose, ears and the taste buds of the tongue.Ciliated simple columnar epithelial cells, but in addition, they Ciliated epithelium is usually found in This movement of the cilia in aColumnar posses fine hair-like outgrowths, cilia on their free the air passages like the nose. It is certain direction causes the mucus,Epithelium surfaces. These cilia are capable of rapid, rhythmic, also found in the uterus and to move (flow or stream) in that wavelike beatings in a certain direction. Fallopian tubes of females. direction. The movement of the cilia propel the ovum to the uterus.Glandular Columnar epithelium with goblet cells is called Inner lining of stomach and salivary specialised gland cells are capableEpithelium glandular epithelium. Some parts of the glandular glands of synthesising and secreting epithelium consist of such a large number of goblet certain substances such as cells that there are only a few normal epithelial cells enzymes, hormones, milk, mucus, left. sweat, wax and saliva.
Connective TissueIt is an animal tissue that is characterized by the abundance ofextracellular components (such as fibers and intercellular substances).The tissue derives its name from its function in connecting, supporting,surrounding or binding cells and tissues.Connective tissue is composed of:•cells•extracellular matrixExtracellular matrix is a special feature that distinguishes connectivetissue from the other tissues of the body. This matrix may be jelly-like,fluid, dense or rigid. The nature of matrix differs according to thefunction of that particular connective tissue.
Muscular tissueMuscles of the body are made up of elongated muscle cells alsoknown as muscle fibre. The movement of the body is broughtabout by the contraction and relaxation of contractile proteinpresent in muscle cells. These contractile proteins are actin andmyosin.
Nervous TissueAll living cells have the ability toreact to stimuli. Nervous tissueis specialised to react to stimuliand to conduct impulses tovarious organs in the bodywhich bring about a response tothe stimulus. Nerve tissue (as inthe brain, spinal cord andperipheral nerves that branchthroughout the body) are allmade up of specialised nervecells called neurons.
Neurons have many different shapes andsizes. However, a typical neuron in a humanconsists of four major regions: a cellbody, dendrites, an axon, and synapticterminals. Like all cells, the entire neuron issurrounded by a cell membrane. The cellbody is the enlarged portion of a neuron thatmost closely resembles other cells. Itcontains the nucleus and other organelles(for example, the mitochondria andendoplasmic reticulum). The dendrites andaxon are thin cytoplasmic extensions of theneuron. The dendrites, which branch out intreelike fashion from the cell body, arespecialized to receive signals and transmitthem toward the cell body. The single longaxon carries signals away from the cell body.In humans, a single axon may be as long as1 meter (about 3 feet). Some neurons thathave cell bodies in the spinal cord haveaxons that extend all the way down to thetoes.
A nerve is anenclosed, cable-likebundle of axons (thelong, slender projectionsof neurons). A nerveprovides a commonpathway for theelectrochemical nerveimpulses that aretransmitted along eachof the axons.