Simple Tissue.pptx

Simple Tissue

1. Permanent or Mature Tissues Cells derived from meristems gradually change in their structure, metabolism and chemistry and acquire specialized characters by their various modes of differentiation. Not all the cells totally differ from the meristems. Some cells retain the power of division and others cannot divide. In a strict sense only those cells which have lost the power for division must be regarded as permanent tissues, but in a broad sense, cells derived from meristem that have acquired a special function like photosynthesis, secretion, storage are treated as part of matured tissue. The cells of these tissues may be living or dead and thin or thick walled. The thin walled tissue are generally living whereas the thick walled may be dead or living. There are two types of mature or permanent tissues: Simple and Complex.

2. Simple P ermanent Tissue: Parenchyma (Para-beside, enchyma-In poured) ( i ) Aerenchyma : (ii) Chlorenchyma: Collenchyma ( Kolla - Glue) Sclerenchyma ( Scleros -hard) Fibers : Sclereids:

3. It is found in every part of the plant body like pith and cortex of stem and root, mesophyll of leaves, flesh of fruits, floral parts and even in xylem and Phloem. Parenchyma cells are oval, rounded and polygonal in shape having well developed spaces among them. The cells are living and contain sufficient amount of cytoplasm in them. Usually each cell possesses one or more nuclei. Generally cells of parenchyma are involved in storage of starch, sucrose, protein, water, phenol derivatives, many mineral substances, etc. Parenchymatous cells may also perform specialized functions and are structurally modified. The turgid parenchyma helps in giving rigidity to the plat body. Partial conduction of water is also maintained through these cells. Parenchyma (Para-beside, enchyma-In poured)

4. The following are the different types of parenchyma. Aerenchyma : Parenchyma in aquatic plants gets modified and the cortex cells possess well developed air spaces.eg Marsilea quadrifolia Intercellular spaces filled with air are large in size and many in number and such tissue are called aerenchyma. Cells occupy a smaller area and the cells are smaller, still they provide the required strength to the aquatic plants. In these plants air spaces are common, helping in aeration and buoyancy. Air spaces are also seen in roots of grasses, petioles(stalk that joins leaf to ste m) of canna, aroids etc. In petiole of Musa stelar kind of aerenchyma is observed.

5. (ii) Chlorenchyma: Cells of photosynthetic parenchyma contain numerous chloroplasts. When parenchymatous cells are exposed to sunlight they develop chloroplast in them and called chlorenchyma. These cells are commonly seen in green parts of plant like leaves, sometimes in young shoots. The chlorenchyma cells also possess large intercellular spaces. Cells of Chlorenchyma are of two types: 1) Palisade cells that is elongated and compactly arranged. 2) Spongy cells that are spaciously arranged and irregularly shaped

6. b) Collenchyma ( Kolla - Glue) Collenchyma is a simple, living tissue composed of elongated cells with acidic heteropolysaccharide .This heteropolysaccharide is called as pectin . Cell walls are thickened due to deposition of pectin. Morphologically it is a simple tissue because of having one type of cells. Collenchyma is the primary supporting tissue in stems, leaves and floral parts of dicots, where as in stems and leaves of monocots collenchyma is usually absent, (instead, sclerenchyma is present in monocots). The most important character of this tissue is its early development and its adaptability to change in rapid growing organ. Collenchyma is usually hypodermal in position just beneath the epidermis and typical supporting organ. Cells are more elongated and narrower than parenchyma. Like parenchyma, collenchyma may also contain chloroplasts or may regain the thickening. Intercellular spaces may or may not be present.

7. Three forms of collenchyma are recognized based on the types of thickenings: i . Thickening is on the tangential wall - lamellar collenchyma . ii. Deposition of pectin is in the corners where several cells meet- angular collenchyma . iii. Thickenings are around the intercellular spaces - tubular or lacunar collenchyma

8. c) Sclerenchyma ( Scleros -hard) Cells of sclerenchyma are thick walled and are usually lignified. The thickness is due to formation of secondary wall. At least initial the secondary wall is free from primary wall. At maturity, usually the cells are devoid of protoplast means they are dead one. The cell wall encloses a cavity lumen and on the cell wall, pits are usually present (simple type). This is supporting tissue that withstands various strains resulting from stretching and bending of plant organ without any damage. They are of various shape and size; even some of these cells are longest in plant kingdom. The primary function of this tissue is to provide mechanical support. Commonly sclerenchyma cells are classified into fibers and sclereids

9. Fibers: These are usually long, spindle shaped structures, with tapering or blunt ends. Longest fiber is seen in Boehmeria nivea (55 cms ). They are arranged in groups. Secondary thickening may account for 90% of the area of the cell; the lumen is narrow. Cells have pits which are very small, round or slit like and often oblique. Fibers are grouped into xylary fibers and extra xylary fibers. Xylary fibers, also called wood fibers are parts of xylem and are longest among xylem elements.

10. The fiber cells are classified according to their mode of origin. They can be classified into three groups: 1- Surface fibers, 2- Wood fibers and 3-Bast fibers. 1. Surface fibers are found in the testa of many seeds and covering of fruits in many plants like cotton ( Gossypium ), coconut, Calotropis sp. etc. These are made up of cellulose and used in stuffing pilose etc.

11. 2. Wood fibers are present in xylem of the stem and roots and also known as xylary fibers. They are of two types: libriform fiber and fiber tracheids . The two differ from each other in their length, thickness of walls and type of pit chambers. The wall in libriform is thick and in tracheids it is thinner, libriform cells have simple pits and tracheids have bordered pits, in libriform cells the pit aperture does not exceed in diameter but exceeds in fiber tracheids .

12. 3. Bast Fibers or phloem fibers are lignified or non-lignified and obtained from the phloem and pericycle of the plant. On account of their elasticity, fibers enable the plant body to withstand various strains. Plants yielding phloem fibers are Corchorus capsularis , Hibiscus cannabis, Tilia sp., Nerium sp., Vinca sp. and Crotolaria juncea etc. These fibers are used in manufacturing of coarse cloth, cordage, ropes,

13. Sclereids: These are shorter than fibers with thick wall and spherical, oval and cylindrical shape. Sclereids occur singly or in groups with lignified walls and cells devoid of living content. Sclereids are commonly found in fruit wall, seed coat, epidermal scales, and occasionally found in cortex, pith, mesophyll and petiole of submerged aquatics. They can be obtained from the endocarp of the almond and coconut and from the hard seed coats of some leguminous seeds ( Pisum , Phaseolus ) The cells devoid of living content and have tubular canals called simple pits. They may be simple or branched. On basis of structure there are many types of sclereids: 1. Asterosclereids are star shaped (Found in leaf)

14. 2. Macrosclereids are similar to palisade cells or rod like shaped (Found in seed coat) 3. Osteosclereids are bone like that are enlarged at their ends (Found in leaf) 4. Brachysclereids are isodiametric like parenchyma (Found in bark, pith and cortex)