planties - . Plant organs are composed of three tissue...

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. Plant organs are composed of three tissue systems: dermal, vascular, and ground. Each organ of a plant has three tissue systems: dermal, vascular, and ground. Each system is continuous throughout the plant body. The dermal tissue is the outer covering. In nonwoody plants, it is a single layer of tightly packed cells, or epidermis, that covers and protects all young parts of the plant. The epidermis has other specialized characteristics consistent with the function of the organ it covers. For example, the root hairs are extensions of epidermal cells near the tips of the roots. The epidermis of leaves and most stems secretes a waxy coating, the cuticle, which helps the aerial parts of the plant retain water. In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots. Vascular tissue, continuous throughout the plant, is involved in the transport of materials between roots and shoots. Xylem conveys water and dissolved minerals upward from roots into the shoots. Phloem transports food made in mature leaves to the roots; to nonphotosynthetic parts of the shoot system; and to sites of growth, such as developing leaves and fruits. The vascular tissue of a root or stem is called the stele. 0 In angiosperms, the vascular tissue of the root forms a solid central vascular cylinder, while stems and leaves have vascular bundles, strands consisting of xylem and phloem. Ground tissue is tissue that is neither dermal tissue nor vascular tissue. In eudicot stems, ground tissue is divided into pith, internal to vascular tissue, and cortex, external to the vascular tissue. The functions of ground tissue include photosynthesis, storage, and support. For example, the cortex of a eudicot stem typically consists of both fleshy storage cells and thick-walled support cells. Plant tissues are composed of three basic cell types: parenchyma, collenchyma, and sclerenchyma. Plant cells are differentiated, with each type of plant cell possessing structural adaptations that make specific functions possible. Cell differentiation may be evident within the protoplast, the cell contents exclusive of the cell wall. Modifications of cell walls also play a role in plant cell differentiation. We will consider the major types of differentiated plant cells: parenchyma, collenchyma, sclerenchyma, water-conducting cells of the xylem and sugar-conducting cells of the phloem. Mature parenchyma cells have primary walls that are relatively thin and flexible, and most lack secondary walls. The protoplast of a parenchyma cell usually has a large central vacuole. Parenchyma cells are often depicted as “typical” plant cells because they generally are the least
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planties - . Plant organs are composed of three tissue...

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