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bio lecture by pauline naive
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  Pauline M. Naïve November 29, 2013 Bio 33.1 Ma’am Anita Mabao  EDA 1.   Describe the permanent tissues Permanent tissues-(matured tissues) are formed by the differentiation of the cells of the meristems (apical and lateral) and are the matured products of the Meristematic activity. These tissues are composed of cells that have lost the power of dividing, having attained their definite form and size. They may be living or dead and thin walled or thick walled. Permanent tissues are divided into 3 group tissues which are the surface/dermal tissues which constitutes the epidermis and periderm, the fundamental/ground tissues which consists of the Parenchyma, Collenchyma, Sclerenchyma, Endodermis, Secretory Tissues and lastly the vascular tissues which are the xylem and phloem. A.   Surface/Dermal Tissues -   Covers the outside of the plant and functions to protect the plants from injury and water loss. It constitutes:    Epidermis- is a dermal tissue of young plants undergoing primary growth and is the outer layer of cells produced by the apical meristems. Its surface layer is one cell thick. It is generally composed of specialized, flattened polygonal cells that occur on all plant surfaces. Shoot surfaces are usually coated with a waxy cuticle which is made up of chitin to prevent water loss and are often covered with hairs, or trichomes, which are epidermal cell extensions. It has a pair of specialized epidermal cells called the guard cells which are found surrounding microscopic pores in all leaves. The guard cells and pores are called stomata (singular stoma), which permits gas exchange (water loss, CO2 uptake, and O2 release or uptake) between the atmosphere and the interior of the leaf. The root epidermis is adapted for absorption of water and minerals, and its outer wall surface typically does not have a waxy cuticle. Extensions from the root epidermal cells, the root hairs , increase the surface area over which absorption can take place. And, the epidermis is usually closely packed, without intercellular spaces or chloroplasts. It functions are to protect the plants against water loss, regulates gas exchange, secretes metabolic compounds and absorbs water and mineral nutrients.    Periderm- is the secondary protective (dermal) tissue that replaces the epidermis during growth in thickness of stems and roots of gymnosperms and dicotyledons. Unlike typical epidermis, the periderm is a multi-layered tissue system, the bulk of which usually constitutes the cork, or phellem.. Phellem (the cork) consists of cells that are dead at maturity, and their primary walls become covered from the inside by the secondary wall which consists of parallel suberin lamellae alternating with wax layers. The lateral meristem, (cork cambium or phellogen), is one cell layer thick and encircles the stem. It produces periderm centrifugally. The layer of cork cells formed is impermeable for water and gases, but is interrupted at certain points by lenticels which function to some extent similar to stomata in the epidermis, and permit gas diffusion. In some cases parenchyma cells are produced centripetally (to the inside of the stem or root) by the phellogen as a part of the periderm. These persistent living cells are called phelloderm and structurally appear similar to cells of the cortex. The number of layers of cork and phelloderm varies greatly among different species; some plants produce no phelloderm. The most important function of the periderm is to reduce the loss of water and solutes  from interior tissues and to protect a plant from unfavourable environmental conditions. B.   Fundamental/Ground tissues -   is a simple non-meristematic tissue (non-dividing tissue) which differentiates from the ground meristem and constitutes most of the primary body of the plant. Ground tissues are covered by the epidermis and it surrounds the vascular tissues. It has several functions which are storage, basic metabolism, support, regeneration, and protection. It is consists of:    Parenchyma- consists of a collection of cells which are more or less iso-diametric that is equally expanded on all sides. Typical parenchymatous cells are oval, spherical or polygonal in shape. Their cells are thin and made of cellulose and are usually living. Parenchyma is universal occurrence in all the soft parts of plants. Its function is mainly storage of food material. Parenchyma containing chloroplasts often called chlorenchyma, manufactures sugar and starch. Star like parenchyma with radiating arms leaving a lot of air cavities is called acrenchyma, as in the petiole of banana and canna and also in many aquatic plants. Parenchyma also has the ability to dedifferentiate and then redifferentiate which means they can change activities and become more specialized and this ability of them to dedifferentiate is important because it is a primary way that plants develop and adapt to various influences such as wounding and changing of the environments. It functions as storage, support to photosynthesis and specialized for short distance transfer of solutes.    Collenchyma- this tissue consists of elongated cells with the corners or intercellular spaces much thickened with a deposit of cellulose and pectin. In a transverse section of the stem the cells look circular or oval. Their walls are provided with simple pits here and there. The cells are living and often contain some chloroplasts. Being flexible in nature collenchyma gives tensile strength to the stem. Containing chloroplasts it also manufactures sugar and starch. Its functions are both mechanical and vital. It has unevenly thickened primary cell walls. They have nonlignified cell walls which can stretch thereby enabling the cells to elongate. Collenchyma cells often differentiate in strands or as a cylinder beneath the epidermis wherein this arrangement maximizes support because a cylinder can provide more support than does a rod like. They are typically arranged in bundles or layers near the periphery of stems or leaf petioles.    Sclerenchyma- consists of very long, narrow, thick walled and lignified cells, usually pointed at both ends. They are fibres like in appearance and hence they are also called sclerenchymatous fibres or simply fibres. They have simple often oblique pits in their walls. The middle Lamella is conspicuous in sclerenchyma. Sclerenchymatous cells are found abundantly in plants and occur in patches or definite layers. They are dead cells and serve a purely mechanical function wherein they give strength and rigidity of the plant body and thus enable it to withstand various strains. Sclerenchyma consists of two types of cells, sclereids and fibers. Both have thick secondary walls and are frequently dead at maturity. Sclereids occur in a variety of shapes, ranging from roughly spherical to branched, and are widely distributed throughout the plant. In contrast, fibers are narrow, elongated cells that are commonly associated with vascular tissues. The main function of sclerenchyma is to provide mechanical support, particularly to parts of the plant that are no longer elongating.       Endodermis- is a specialized layer of cortex found at the boundary between the ground tissue and the vascular tissue in roots, and occasionally in stems. This single layer of cells srcinates from cortical tissue at the innermost layer of the root cortex and forms a cylinder that surrounds the central vascular tissue, or stele. Early in root development, a narrow band composed of the waxy substance suberin is formed in the cell walls circumscribing each endodermal cell. These suberin deposits, called Casparian strips, form a barrier in the endodermal walls to the intercellular movement of water, ions, and other water-soluble solutes to the vascular cells. And is responsible for the regulation of water flow and dissolved substances into and out of the cell.    Secretory Tissues- the tissues which are concerned with special functions like secretion or excretion of different kinds of substances like resins, latex, gums, nectar etc. are called special or secretory tissue. These tissues are of two main types: Laticiferous tissue which are long, thin walled living, multinucleate and profusely branched tube like tissues. They contain milky juices called latex. These tissues are irregularly distributed in parenchymatous tissues. And then Glandular tissues which are tissues that are made up of glands. The glands are well organized and specialized structures which contain some secretary or excretory products. They occur either single cells or in groups. Glands may be external or internal. External glands superficial in nature and formed on epidermis. They may occur as hydathodes, glandular hairs, nectarines and digestive glands etc and then internal glands which are confined to internal tissues. They are formed by lysis of some of the cells or by splitting of cells at middle lamella. They occur as oil glands, mucilage secreting glands etc. These tissues occur in most vascular plants. The cells of secretory tissues usually contain numerous mitochondria. The frequency of other cell organelles varies according to the material secreted. In most glandular trichomes the side wall of the lowest stalk cell is completely cutinized. This prevents the secreted material from flowing back into the plant. C.   Vascular Tissues -   is a complex conducting tissue, formed of more than one cell type and are specialized for long-distance transport of water and dissolved solutes. They consist of:    Xylem- transports water and mineral ions from the root to the rest of the plant. The tracheids and vessel elements are the conducting cells of the xylem. Both of these cell types have elaborate secondary-wall thickenings and lose their cytoplasm at maturity; that is, they are dead when functional. Tracheids overlap each other, whereas vessel elements have open end walls and are arranged end to end to form a larger unit called a vessel. Other cell types present in the xylem include parenchyma cells, which are important for the storage of energy-rich molecules and phenolic compounds, and sclerenchyma fibers.    Phloem- distributes the products of photosynthesis and a variety of other solutes throughout the plant. The sieve elements and sieve cells are responsible for sugar translocation in the phloem. The former are found in angiosperms; the latter perform  the same function in gymnosperms. Like vessel elements, sieve elements are often stacked in vertical rows, forming larger units called sieve tubes, whereas sieve cells form overlapping arrays. Both types of conducting cells are living when functional, but they lack nuclei and central vacuoles and have relatively few cytoplasmic organelles. Substances are translocated from sieve cell to sieve cell laterally through circular or oval zones containing enlarged pores, called sieve areas. In contrast, sieve tubes translocate substances through large pores in the end walls of the sieve elements, called sieve plates. Sugar movement through sieve tubes is more efficient and rapid than through sieve cells and represents a more evolutionarily advanced mechanism. Sieve elements are associated with, and depend on, densely cytoplasmic parenchyma cells called companion cells. The analogous cells adjacent to the sieve cells of gymnosperms are called albuminous cells. Companion cells provide proteins and metabolites necessary for the functions of the sieve tube elements. In addition, the phloem frequently contains storage parenchyma and fibers that provide mechanical support. 2.   Differentiate the 3 Life span of Plants    Annual- are plants surviving just for one growing season.    Biennial- are plants that takes two years to complete its biological lifecycle.    Perennial- are plants that lives for more than two years.
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