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Tissues

This document summarizes the different types of plant tissues. It describes two main categories of plant tissues - meristematic and permanent tissues. Permanent tissues are further divided into simple and complex tissues. Simple tissues include epidermis, parenchyma, collenchyma, sclerenchyma and cork. Complex tissues include xylem and phloem. Each tissue type is then defined and their structure and functions are explained.

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B-pharm• 2nd-sem• 1st-Year•
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Plant Tissues DEFINITION- An aggregation of similar cells having same functions is known as tissue. Depending on origin, structure and physiology, plant tissues can be classified as 1. Meristematic or embryonic tissue 2. Permanent tissue a. Simple permanent tissues b. complex permanent tissues
Differences
2 • Simple permanent tissue • 1. Epidermis • 2. Parenchyma • 3. Collenchyma • 4. Sclerenchyma • 5. Cork • Complex permanent tissue • 1. xylem • 2. Phloem
EPIDERMIS Outermost cellular layer  Covers the whole plant structure  Covers roots, stem, leaves, flowers and fruit.  Living cells.  Closely packed, without intercellular spaces or chloroplasts.  Outer wall thickened, covered by a waxy, waterproof cuticle which are made up of cutin. Stomata found in the epidermis of leaves and stem.  root hairs (trichomes) found in the epidermis of leaves and stems.
3  A stoma is an opening (pore)  Which is bounded by two bean shaped cells called guard cells .  Guard cells are covered by various numbers of subsidiary cells. Stomata 5 types 1. Paracytic 2. Diacytic 3. Anisocytic 4. Anomocytic 5. Actinocytic structure
4 Types of stomata
Structure of epidermal cell • 1. Straight walled polygonal • 2. Thick walled beaded • 3. wavy walled
Functions  Protect the underlying cells.  Cuticle prevents the loss of moisture from 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.  Help in transpiration, water vapor may be given off through the stomata.  Trichomes excrete water and volatile oils etc.
Parenchyma  Composed of living cells  Thin-walled, made with cellulose.  Found in all organs of higher plants.  Iso-diametric  Intercellular space is present.  Contain vacuolated protoplast.  Main function is manufacturing and storage of food.
7 The secondary thickening may give rise to various types of parenchyma, such as 1. simple parenchyma. 2. Parenchyma with intercellular space. 3. lignified parenchyma 4. Reticulate parenchyma
Collenchyma  Supporting tissue  found underneath of epidermis of stem. leaf  Thick, soft, plastic and non-lignified cell wall.  Walls have lots of pectin, which holds water.  Also contains lots of cellulose in the cell wall.  Generally longer than parenchyma cells.  Cells have protoplast, chloroplasts are normally absent.  Thick walled cells give mechanical support to plant.
9 Type of collenchyma 1. Angular - Walls thickened where cells meet in the corners. 2. Lamellar or plate – thickened on tangential walls. Cells appear to line up in rows just below epidermis. 3. Lacunar, i.e. with a hole - thickening around the spaces between the cells. Hole may be closed later by pectin substances.
Sclerenchyma • Mature sclerenchyma cells are dead. • Have secondary cell walls thickened with cellulose and usually impregnated with lignin. • The cell cavity or lumen is very small or it may disappear completely. • It is found in stems, roots and leaves. Functions: • sclerenchyma is an important supporting tissue in plants, provide mechanical support plant. • sclereids are responsible for the hardness of seeds and the shell of walnut. • fibres probably play a role in the transport of water in the plant,
11 There are two types of sclerenchyma cells, namely sclereids and fibres. Sclereids:  The cells are irregular in shape.  The cell walls are thick, hard and lignified which makes the lumen very small.  Simple pits (canals) are found in the thickened cell walls and link adjacent cells.  Sclereids are commonly found in fruit and seeds.  They are found in groups or single.
12 Fibres:  The cells are needle-shaped with pointed tips, thick walls and rather small lumen.  Secondary cell walls, impregnated with, are formed.  Simple pits are also present.  Fibres are abundant in the vascular tissue of angiosperms, i.e. flowering plants.  They are also called as internal hairs.  They gradually loose protoplast and become dead.  They are pericyclic fibres, xylem fibres, phloem fibres etc.
CORK  Cork is a tissue found in many vascular plants as part of the periderm.  The cork is a lateral meristem  A mature cork cell is non-living.  Cell walls are composed of a waxy substance that is highly impermeable to gases and water called suberin.  cork cell may be filled with air or may contain traces of lignin, tannins, or fatty acids.  May vary in thickness from one to the next.  Packed closely together.
14  Cells are generally arranged in radial rows.  Separation among the cells is achieved by structures arising from the cork cambium called lenticels.  These pore-like structures allow gases to be exchanged between the plant stem and the outside environment.  The cork cambium provides the internal cells of the plants with extra insulation and protection.
Xylem • Xylem is one of the transport tissue in vascular plants. • The basic function of xylem is to transport water, but it also transports some nutrients. • Give mechanical support to the plant. • Composed of tracheids, tracheae or vessel, xylem parenchyma and xylem fibres. • Tracheids are elongated cells with large cavities and tapering end. • tracheids are dead cells.
15 • Cell wall is hard, lignified with bordered pits. Vessel/trachea: • They are long tube like bodies. Trachae is formed from a row of cylindrical cells. • The cell wall is hard & lignified with annular to pitted. • It should be noted that trachied is a single cell, but a trachea or vessel is a tube like body formed from a row of cells.
20 • The initially formed xylem vessels are smaller cavities & annular with spiral thickening called as Protoxylem vessel. • But lately formed vessels are reticulate with pitted thickening called metaxylem vessel.
21
Types of xylem vessel
PHLOEM • Phloem is the living tissue . • The phloem is the innermost layer of the bark. • The phloem is concerned mainly with the transport of soluble organic material made during photosynthesis. • Phloem composed of Sieve tube, Companion cell, phloem parenchyma also phloem fibres.
Phloem
• Seive tube is living, having lining cytoplasm with a large central vacuole. • The nucleus disintegrates with the maturity of the tube. • Cell wall is thin & made up of cellulose. • Vacuole is rich in nitrogenous matter. • A carbohydrate called callose is deposited on the seive plate in the form of a pad called callous pad. • Companion cells are closely associated with sieve tubes & are connected with them by pores.