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kuliah anatomi akar

Nov 18, 2014

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The growth in length of a root

through the division and elongation of cells located in the apical portion of the root.

The tip of the root is covered by a mass of cells called the root cap. The cells of the root cap are parenchyma, and frequently have thick, mucilage-containing walls.

The root cap protects the root meristem and lubricates the tip to pushed through the soil. The root cap also appears to play a role in the roots response to gravity. Starch-containing plastids may act as statoliths, or gravity-sensing bodies.

The quiescent Center is a relatively inactive of slowly dividing cellsFungsi ?

Surrounding the quiescent center is the apical meristem which actively divides

The epidermis arise from protoderm The cortex from the ground meristem The vascular tissue from the procambium.

The cortex between the epidermis and the vascular cylinder The cortex is composed of parenchyma cells which frequently store starch. There are air spaces between the cells. The innermost layer of the cortex is called the endodermis (a cylinder of tightly packed cells without intercellular spaces).

The endodermis The endodermis separates the Cortex from the Stele an endodermis to regulate water uptake by the roots and maintain the water balance of the plant The Exodermis has the same anatomy as the Endodermis and probably restricts water loss to the outside in older roots.

The cells of the endodermis have specialized walls that known as the Casparian strip The specialized walls, composed of a mixture suberin and lignin

The presence of the Casparian strip makes the walls impervious to water, so that all substances entering the vascular tissue must pass through the cytoplasm of the endodermal cells.

The walls of the epidermis and the cortical cells form a continuous system through which water and dissolved substances can diffuse without entering the cytoplasm; that is, until they reach the endodermis, where the way is blocked by the Casparian strip. Here, any substance entering the vascular tissue must pass through the cytoplasm of the endodermal cells where, presumably, the flow is regulated

STELE

The vascular tissue, or stele, at the center of the root. The stele is composed of xylem and phloem, and is surrounded by the pericycle. The pericycle is the outermost layer of the stele and is directly beneath the endodermis. In young roots the pericycle is composed of thin-walled parenchyma cells, but in older roots the walls may become thickened.

The cells of the pericycle retain their meristematic capacity and are the site of formation of secondary roots.

The cells of the metaxylem Differentiate, larger in diameter than the protoxylem They are located inside protoxylem and may occur in the center of the root if pith is not present If pith is present, the metaxylem forms a ring around it

The phloem consists of protophloem and metaphloem. The direction of differentiation and maturation of the phloem is the same as the xylem, namely from the younger portions of the root toward the mature and from the edges toward the center.

Lateral (Secondary) Roots Lateral

(Secondary) Roots originate in the Stele or the Endodermis. They grow through the Cortex and Epidermis Vascular Connection between it and the parent Stele

in most angiosperms The pericycle of the root is usually a single-cell-layer thick. It retains its ability to divide long after the other cells of the root have lost this ability.

Because of this capacity, it is the site of formation of the secondary roots. It also functions in the thickening of the root during secondary growth

The first sign of secondary root initiation is the periclinal division of a limited number of periderm cells. These are followed by divisions in both periclinal and anticlinal planes. These divisions result in the formation of a group of meristematic cells that soon becomes organized into an apical meristem having the same pattern as the parent root.

As this new apical meristem grows, it pushes its way through the cortex and epidermis of the parent root. As the tissues of the new root differentiate and mature, the xylem and phloem develop, so that they become continuous with the xylem and phloem of the parent root.

cells that remain undifferentiated between the primary phloem and primary xylem form the vascular cambium that gives rise to the secondary phloem and secondary xylem.

Divisions of the pericycle initiate the formation of the cambium. The cambium differentiating from the provascular tissue between the phloem and xylem and from the pericycle over the protoxylem poles.

THE DIFFERENCE THE DIFFERENCE MONOCOTYL AND MONOCOTYL AND DICOTYL ROOT DICOTYL ROOT

Number of Xylem ArmsTwo = Diarch Three = Triarch Four = Tetrarch Five = Pentarch Six = Hexarch More than five = Polyarch

Monocots are usually Polyarch

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