Epidermis

Epidermis

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  EPIDERMIS Presented by: AminaAbbas Roll#06 5th Botany(Evening) IUB
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  Contents ■ Epidermis ■ Structure& Development ■ Functional & Evolutionary Specialization
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  Epidermis: The epidermis isthe outermost cellular layer which covers the whole plant structure, i.e. it covers roots, stem, leaves.
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  Structure & Developmentof Epidermis:  It is composed of a single layer of living cells, although there are exceptions.  Epidermis is usually closely packed, without intercellular spaces or chloroplasts. Instead, the epidermis is like a clear spray coating whose sole purpose is to protect the plant from the elements, while still letting the sun shine in. That's particularly important for a leaf because their main job is to photosynthesize. Composition of Epidermis: ■ Epidermal Proper Cells ■ Specialized cells ■ Stomatal Guard Cells ■ Trichomes
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  Epidermal Proper Cells: ■These cells vary in thickness and shape ■ The outer walls, which are exposed to the atmosphere and usually thickened, and may be covered by a waxy, waterproof cuticle which are made up of cutin. Apart from the normal epidermal cells there are also stomata in the epidermis of leaves and stem. ■ Wax in the form of granules or rods may be deposited on the surface of cuticle as continuous.
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  Specialized Epidermal Cells: ■In certain species of pteridophytes and gymnosperm, many species of Graminae and certain dicots, fiber- like epidermal cells are formed. ■ In Graminae and many other monocots ,bubble-like cells are formed called Bulliforms cells, these cells are larger then normal epidermal cells and are thin walled. Function: ■ These cells are concerned with opening of rolled leaf as enclosed in bud. ■ Rolling and unrolling of mature leaves as a result of loss and uptake of water.
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  Stomatal cells: ■ Astoma is an opening (pore) which is bounded by two bean shaped cells called guard cells and two to four subsidiary cells that lack chloroplasts. ■ The guard cells differ from normal epidermal cells in that they have chloroplasts and the cell walls are thickening unevenly; the outer wall is thin and the inner wall (nearest the opening) is thick. ■ The leaf and stem epidermis is covered with pores called stomata (sing., stoma), part of a stoma complex consisting of a pore surrounded on each side by chloroplast-containing guard cells.
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  Trichomes: ■ The thin-walledepidermal cells of roots give rise to root hairs. Hair- like outgrowths may also be found in the epidermis of leaves and stems. The epidermal cells of roots that produce root hairs are called trichoblasts, whereas epidermal cells without the capability of root hair formation are called as atrichoblasts.
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  Evolutionary Specialization ■ Theplant epidermis is a multifunctional tissue playing important roles in water relations, defense and pollinator attraction. This range of functions is performed by a number of different types of specialized cells, which differentiate from the early undifferentiated epidermis in adaptively significant patterns and frequencies. These various cells show different degrees of morphological specialization.
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  Function of Epidermis: ■The epidermal cells protect the underlying cells. ■ The waxy cuticle prevents the loss of moisture from the leaves and stems. ■ The transparent epidermal cells allow sunlight (for photosynthesis) to pass through to the chloroplasts in the mesophyll tissue. ■ The stomata of leaves and stems allow gaseous exchange to take place which is necessary for photosynthesis and respiration. ■ Water vapour may be given off through the stomata during transpiration. ■ The root-hairs absorb water and dissolved ions from the soil.