Tissue and tissue system

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A tissue is an organization of cells that work together to perform a particular function

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Tissue: A tissue is an organization of cells that work together to perform a particular function.:

Tissue: A tissue is an organization of cells that work together to perform a particular function.

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Classification of Plant Tissues

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Meristematic Tissue # cells that do not differentiate # cells retain the ability to divide # Types: Apical – primary growth at root and shoot tips Lateral – secondary growth in trees and shrubs Intercalary – secondary growth in monocot stems

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Location of Meristematic Tissues

Apical meristem:

Apical meristem procambium  gives rise to 1o vascular tissue protoderm  gives rise to epidermis Cells that form at apical meristems : ground meristem  gives rise to ground tissue Lengthen shoots and roots: SAM and RAM Root cap Apical meristem Region of cell differentiation/maturation Region of cell elongation Region of cell division

Lateral meristem:

Lateral meristem Vascular cambium  2o vascular tissue Cylindrical arrays of cells Beneath the bark, in vascular bundles of dicot stems Cork cambium  periderm Increases girth of older roots and stems Basswood – stem in cross section; 1, 2, 3 year old stems

Intercalary Meristems:

Intercalary Meristems Between permanent tissues Represents the remnant of the apical meristem Particularly common at the nodal regions Contributes towards the increase in length Responsible for the formation of branches at the nodal regions

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PARMANENT TISSUE Protoplasm may be present or absent in the cells at maturity. Cell wall is thin or thick. Intercellular spaces may be present. Cells contain ergastic sub­stances. Metabolic activities are relatively slow. Cell wall is composed of sub­stances such as lignin, hemicellulose etc. “The tissues in which the power of division of cells is lost, either permanently or temporarily called perma­nent tissues. Permanent tissues develop from the derivatives of various meristems.”

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collenchyma parenchyma sclerenchyma Morphology of three simple tissue types:

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Parenchyma cells Cells are pliable, thin walled, many sided Cells remain alive at maturity and retain capacity to divide Mesophyll is a type of parenchyma that contains chloroplasts Nucleus is present and hence living Location: Soft parts of plat – Cortex of root, ground tissues in stem, mesophyll of leaves. Functions: Photosynthesis & respiration Storage (starch, oil droplets, water, and salts) Wound healing & regeneration

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Parenchyma Cell vacuole Thin cell wall Cytoplasm

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Collenchyma cells Cells are elongated, circular, oval or polygonal in cross-section. Elongated cells that have unevenly thickened cell walls Nucleus is present and hence the tissue is living. Alive at maturity flexible support system If they contain chlorophyll they are known as chlorenchyma. Location: Below the epidermis of dicot stem and petiole (Absent in monocot). Functions: Provide tensile strength to plants Allows easy bending in various parts of plant without actually breaking it Containing chlorophyll they produce food

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Collenchyma Cytoplasm Nucleus Thick cell wall

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Sclerenchyma Cells The cells are long, narrow, thick and lignified, usually pointed at both ends. Cell wall is evenly thickened with lignin and sometimes is so thick that the cell cavity or lumen is absent Nucleus is absent and hence the tissue is made up of dead cells Location: In stem around vascular bundle, roots, veins of leaves, hard covering of seeds and nuts. Found in woody plants. Functions: Gives mechanical support by giving rigidity, flexibility and elasticity to the plant body. Fibres probably play a role in the transport of water Containing chlorophyll they produce food

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There are two types of sclerenchyma cells SCLERIDS FIBERS Sclereids are developed from parenchyma cells that are secondarily modified. Deposit thick secondary walls that are heavily lignified Sclereids may pack together very densely. They are often referred to as “stone cells”. Sclereids are found in fruits such as pears and this give them their gritty texture. Fibers are derived from meristematic cells and differentiate early into elongated cells with few simple pits in their cell walls. Found often in association with vascular tissues (particularly phloem in primary growth and secondary xylem), also in the cortex, secondary phloem of tree bark also exhibits fibers.

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Complex Tissues Inside or between organs and supports and binds other tissues The cells are thorougly scattered. Called vascular tissue in plants. Support plant body Two types of complex tissue: Xylem Conducts water and dissolved minerals from the roots Phloem Conducts dissolved food materials, carbohydrates, in solution Together they constitute vascular bundles. “Complex tissues are made up of more than one type of cells and they work together as a unit. They transport water, salt and prepared food material to various parts of the plant body.”

Xylem:

Xylem Conducts water from roots to above ground plant parts. It contains conducting cells called tracheary elements Conducting cells are dead and hollow at maturity. Tracheids are evolutionarily more ancient tracheary elements found in gymnosperms. Both tracheary elements and tracheids undergo apoptosis(die) and do their jobs as empty cells (only the cell walls remain). vessel member tracheids

Phloem:

Phloem Phloem transports sugars, proteins and minerals around the plant. In flowering plants, phloem is contains four cell types: sieve tube members, companion cells, fibres and parenchyma Main conducting cells are sieve-tube members Companion cells assist in the loading of sugars companion cells which supply the RNA and proteins that keep the sieve tube member cell alive. sieve plate sieve-tube member companion cell

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Vascular Bundles with xylem & phloem Maize or Corn – vein in cross section Alfalfa – vein in cross section

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Secretory Tissues Secretory tissues occur in most vascular plants. Some of these tissues, such as hydathodes, salt glands and nectaries, secrete unmodified or only slightly modified substances supplied directly or indirectly by the vascular tissues. Other tissues secreting, for instance, polysaccharides, proteins and lipophilic material, produce these substances in their cells Two types of secretory tissue: 1. Laticiferous tissue 2. Gladular tissue “Organizations of cells which produce a variety of secretions is called secretory tissue.

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Plant Tissue Systems VASCULAR TISSUES GROUND TISSUES SHOOT SYSTEM ROOT SYSTEM EPIDERMIS There are 3 type of plant tissue systems: Ground tissue system Vascular tissue system Dermal tissue system “Large units of tissues having some features in common are called tissue systems”

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Vascular Tissue System The vascular system consists of complex tissues, the phloem and the xylem.The xylem and phloem together constitute vascular bundles. It is the conductive or “plumbing” system of the plant. The phloem transports carbohydrates from sites of production (sources such as leaves) to sites of utilization for energy or where it is being stored (sinks) elsewhere in the plant.

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The dermal tissue system is the outer covering of the plant . The dermal tissue system consists of the epidermis and the periderm . All parts of young plant body covered by an epidermis,which is a single layer or multiple layers of cells. The epidermis contains epidermal cells and other specialized cells such as guard cells. The shoot epidermis secretes a layer of wax-covered cutin, the cuticle, which helps retard water loss from stems and leaves. Dermal Tissue System Epidermis Cell

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Ground Tissue System The ground tissue system synthesizes organic compounds, supports the plant and provides storage for the plant. It is mostly made up of parenchyma cells but can also include some collenchyma and sclerenchyma cells as well. Ground tissue functions primarily in storage, support, photosynthesis, and the production of defensive and attractant substances (oils and toxins).

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