2.1 PLANT TISSUE HALIMAHTUN SAEDIAH BT ABU BAKAR KOLEJ TEKNOLOGI TIMUR

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2.1 PLANT TISSUE HALIMAHTUN SAEDIAH BT ABU BAKAR KOLEJ TEKNOLOGI TIMUR GENERAL Plant cell are differentiated possessing structural adaptations that make specific functions possible.

1 2.1 PLANT TISSUE HALIMAHTUN SAEDIAH BT ABU BAKAR KOLEJ TEKNOLOGI TIMUR GENERAL Plant cell are differentiated possessing structural adaptations that make specific functions possible. Modifications of cell walls also play a role in plant cell differentiation. Major types of differentiated plant cells: 1. Parenchyma 2. Collenchyma 3. Sclerenchyma 4. water-conducting cells of the xylem 5. sugar-conducting cells of the phloem TYPES PLANTS TISSUES Dermal tissues: Epidermis and periderm Ground tissues: Basic Cell: Parenchyma, collenchyma, sclerenchyma (Modified parenchyma) Vascular tissues: phloem and xylem DERMAL TISSUES The dermal tissue is the outer covering. Guard cells: a. To facilitate gas exchange between the inner parts of leaves, stems, and fruits, plants have a series of openings known as stomata (singular stoma). b. These openings would allow gas exchange, but at a cost of water loss. c. Guard cell are bean-shaped cells covering the stomata opening. They regulate exchange of water vapor, oxygen and carbon dioxide through the stoma STOMATA In non woody plants: It is a single layer of tightly packed cells, or epidermis that covers and protects all young parts of the plant. The epidermis has other specialized characteristics consistent with the function of the organ it covers. For example: The root hairs are extensions of epidermal cells near the tips of the roots. The epidermis of leaves and most stems secretes a waxy coating, the cuticle, which helps the aerial parts of the plant retain water. 1

2 In woody plants: Protective tissues periderm replaces the epidermis in older regions of stems and roots. GROUND TISSUES Parenchyma 1. Mature parenchyma cells have primary walls that are relatively thin and flexible, and most lack secondary walls. 2. The protoplast of a parenchyma cell usually has a large central vacuole. 3. Parenchyma cells typical plant cells because they generally are the least specialized, but there are exceptions. For example: the highly specialized sievetube members of the phloem are parenchyma cells. GROUND TISSUES Parenchyma LEAF STRUCTURE 4. Parenchyma cells perform most of the metabolic functions of the plant, synthesizing and storing various organic products. 5. For example: photosynthesis occurs within the chloroplasts of parenchyma cells in the leaf. Some parenchyma cells in the stems and roots have colorless plastids that store starch. The fleshy tissue of most fruit is composed of parenchyma cells. Most parenchyma cells retain the ability to divide and differentiate into other cell types under special conditions, such as the repair and replacement of organs after injury to the plant. Characteristic: large, thin-walled, and usually have a large central vacuole In areas not exposed to light, colorless plastids predominate and food storage is the main function. The cells of the white potato are parenchyma cells. Where light is present, e.g., in leaves, chloroplasts predominate and photosynthesis is the main function. 2

Palisade parenchyma cells are elogated cells located in many leaves just below the epidermal tissue. Palisade mesophyll: Column-shaped cells found below the upper epidermis.

They are loosely packed with many large intercellular spaces for gaseous exchange. They have fewer chloroplasts than palisade cells to carry out photosynthesis.

3 Palisade parenchyma cells are elogated cells located in many leaves just below the epidermal tissue. Palisade mesophyll: Column-shaped cells found below the upper epidermis. The cells contain many chloroplasts to carry out photosynthesis. Spongy mesophyll cells occur below the one or two layers of palisade cells Isodiametric or irregular-shaped cells. They are loosely packed with many large intercellular spaces for gaseous exchange. They have fewer chloroplasts than palisade cells to carry out photosynthesis. Endodermis: Consists of a single-celled ring which forms a selective barrier between the outer contex and the inner pericycle tissue. In roots, the endordermis cells are impregnated with to form a distinctive Casparian strip and prevent the movement of water via the apoplast pathway. Non-suberised passage cells in the endordermis permit lateral movement of water and mineral salts. The endordermis cells contain starch granules as energy store. Mineral ions are actively secreted into the xylem vessels to maintain the root pressure. Pericycle One to several layers of parenchyma cells. Pericycle is found between the endordermis and the central vascular tissues. It can divide to produce the lateral roots and is involved in the secondary growth of roots. Collenchyma Cells Have thicker primary walls than parenchyma cells, though the walls are unevenly thickened. Grouped into strands or cylinders, collenchyma cells help support young parts of the plant shoot. Young stems often have strands of collenchyma just below the epidermis, providing support without restraining growth. Mature collenchyma cells are living and flexible and elongate with the stems and leaves they support. 3

Sclerenchyma Cells Have thick secondary walls usually strengthened by lignin and function as supporting elements of the plant. They are much more rigid than collenchyma cells.

Many sclerenchyma cells are dead at functional maturity, but they produce rigid secondary cells walls before the protoplast dies.

Two types of sclerenchyma cells, fibers and sclereids, are specialized entirely for support. Fibers are long, slender, and tapered, and usually occur in groups.

4 Sclerenchyma Cells Have thick secondary walls usually strengthened by lignin and function as supporting elements of the plant. They are much more rigid than collenchyma cells. Unlike parenchyma cells, they cannot elongate. Sclerenchyma cells occur in plant regions that have stopped lengthening. Many sclerenchyma cells are dead at functional maturity, but they produce rigid secondary cells walls before the protoplast dies. In parts of the plant that are still elongating, secondary walls are deposited in a spiral or ring pattern, enabling the cell wall to stretch like a spring as the cell grows. Two types of sclerenchyma cells, fibers and sclereids, are specialized entirely for support. Fibers are long, slender, and tapered, and usually occur in groups. Those from hemp fibers are used for making rope, and those from flax are woven into linen. Sclereids are irregular in shape and are shorter than fibers. They have very thick, lignified secondary walls. Sclereids impart hardness to nutshells and seed coats and the gritty texture to pear fruits. VASCULAR TISSUE INTRODUCTION The vascular tissue of a root or stem is called the stele In angiosperm, the vascular tissue of the root forms a solid central vascular cylinder, while stems and leaves have vascular bundles, strands consisting of xylem and phloem. 4

5 INTRODUCTION TO XYLEM Continuous throughout the plant, is involved in the transport of materials between roots and shoots. Xylem conveys water and dissolved minerals upward from roots into the shoots. INTRODUCTION TO XYLEM Four types of cells: 1. Vessels 2. Tracheids 3. Fibres 4. Xylem parenchyma INTRODUCTION TO PHLOEM Phloem transports food made in mature leaves to the roots; to non photosynthetic parts of the shoot system; and to sites of growth, such as developing leaves and fruits. Xylem: The water conducting elements of xylem, the tracheids and vessel elements, are elongated cells that are dead at functional maturity. The thickened cell walls remain as a non living conduit trough which water can flow. Both tracheids and vessels have secondary walls interrupted by pits, thinner regions where only primary walls are present. Xylem: Tracheids are long, thin cells with tapered ends. Water moves from cell to cell mainly through pits. Because their secondary walls are hardened with lignin, tracheids function in support as well as transport. Vessel elements are generally wider, shorter, thinner walled, and less tapered than tracheids. Vessel elements are aligned end to end, forming long micropipes or xylem vessels. The ends are perforated, enabling water to flow freely. Xylem vessels: These are only found in the xylem tissue of flowering plants. Most water travels in the xylem vessels. Xylem vessels are formed from a column of tubular cells. The end cross-walls break down so that the cells (xylem elements) combine to form a continuous long tube. 5

Xylem vessels: The walls of these tubes become strengthened by the deposition of lignin. The lignified walls are impermeable to water, solutes and gases. Xylem vessels are composed of dead cells.

The xylem of angiosperms contains more vessels and less tracheids. Tracheids are generally longer but more narrow than vessel elements.

6 Xylem vessels: The walls of these tubes become strengthened by the deposition of lignin. The lignified walls are impermeable to water, solutes and gases. Xylem vessels are composed of dead cells. There is no protoplasm in the xylem vessels and hence more water can flow through the hollow continuous tube with less friction. Tracheids The xylem of ferns and conifers contains only tracheids. The xylem of angiosperms contains more vessels and less tracheids. Tracheids are generally longer but more narrow than vessel elements. They are elongated spindle-shaped single cells with tapering end walls. The tapered ends of the tracheids overlap and interlock with one another further increasing their combined strength. The cell walls are lignified. When mature, tracheids are dead cells with empty lumens. Pits are present in the walls to allow water to move from one tracheid to another and also to the surrounding living cells. Tracheids transport water and mineral ions but are less efficient than vessels. They do not have large perforated or open ends between the cells and water has to move through smaller pits. Xylem fibres: These are similar in structure to sclerenchyma fibres: They are dead cells with thickened lignified walls. They help to support the plant body and are not involved in water transport. 6

In angiosperm, phloem of sieve tubes element, companion cells, phloem parenchyma, fibres and sclereids. A sieve tube: Consist of sieve elements(sieve cells) joined together to Form a long tube.

7 Xylem parenchyma: The xylem parenchymas are living cells. They act as packaging tissue in the primary xylem. In secondary xylem, the parenchyma cells form radial medullary rays which function in radial transport of food and water, gases and food storage. PHLOEM Phloem is a component of the vascular tissue. In angiosperm, phloem of sieve tubes element, companion cells, phloem parenchyma, fibres and sclereids. A sieve tube: Consist of sieve elements(sieve cells) joined together to Form a long tube. Their end walls are perforated forming sieve plates with sieve pores. This allows cytoplasmic connections between the sieve elements and the flow of liquid from one sieve element to the next. The cells are alive, with thin cellulose cell walls and protoplasm. As the cells mature some of the organelles for example, the nucleus, ribosomes and the Golgi apparatus degenerate. A sieve tube: This leaves a narrow layer of cytoplasm containing few small mitochondria and endoplasmic reticulum at the periphery to facilitate smooth flow of soluble food. In some plants the sieve tube elements also contain fibrous phloem proteins. Companion cells: Companion cells are found only in the angiosperm. They are adjacent and closely associated with the sieve tube elements. Companions cells have a nucleus, dense cytoplasm with small vacuoles. They are metabolically active and have numerous mitochondria and ribosomes. The companion cells are linked by numerous plasmodesmata to sieve elements. Companion cells move sugars such as sucrose and amino acids into the sieve elements. 7

8 Phloem fibres and sclereids: They occur occasionally in the primary phloem but are more common in the secondary phloem of dicotyledons. They help to support other phloem cells when the plant is growing. Phloem parenchyma: Phloem parenchyma is only found in dicotyledonous plants. They act packaging tissue in the primary phloem. In secondary phloem, the cells for radial medullary rays. Phloem parenchyma: Function of phloem: Translocation of organic products of photosynthesis. Sugars and amino acids for example, are translocated from the leaves ( source ) to other parts ( sinks ) of the plant such as the meristem and roots where are utilised or stored. Phloem parenchyma: The companion cells are closely associated with the sieve elements, actively move substances such as sugars and amino acids into the sieve elements. EUDICOT & MONOCOT SYSTEM In eudicot stems, ground tissue is divided into pith, internal to vascular tissue, and cortex, external to the vascular tissue. The function of ground tissue includes photosynthesis, storage, and support. For example, the cortex of a eudicot stem typically consists of both fleshy storage cells and thick-walled support cells. A eudicot stem. eudicot stem (sunflower), with vascular bundles forming a ring. Ground tissue toward the inside is called pith, and ground tissue toward the outside is called cortex. A monocot stem. A monocot stem (maize) with vascular bundles scattered troughout the ground tissue. In such an arrangement, ground tissue is not partitioned into pith andcortex. SUMMARY OF PLANT TISSUES: Cell type Distribution Cell shape and structure. Parenchyma Cortex, pith, ground tissue in xylem and phloem. Living cells. Usually isodiametric, sometimes elongated. Thin cell wall contains cellulose, hemicellulose and pectin. Large central vacuole, thin layer of cytoplasm and nucleus push to the periphery. Function Ground tissue in stems and roots. Turgid cells give support especially to herbaceous. Metabolically active. Stores food. Permits transport of food through apoplast or symplast pathways. Large intercellular spaces gaseous exchanges. Some parenchyma cells are modified to form specialized cells e.g. epidermis, mesophyll, endodermis and pericycle. 8

9 SUMMARY OF PLANT TISSUES: Cell type Distribution Cell shape and structure. Collenchyma Below epidermis, midribs of leaves, leaf petioles. Sclerenchyma Below epidermis xylem and phloem, pericycle of some stems. Living cells. Polygonal, elongated with tapering ends. Uneven thickenings of cell walls, usually at the corners of cell walls with deposits of cellulose, pectin and hemicellulose. Dead cells. Lignified walls. Polygonal, elongated with overlapping and interlocking tapering ends. Function Gives mechanical support, flexibility. Some cells contains chloroplast that carry out photosynthesis. Supporting tissue. SUMMARY OF PLANT TISSUES: Cell type Distribution Cell shape and structure. Xylem vessels and tracheids Phloem sieve tubes and companion cells. Vascular tissue Dead cells. Lignified walls. Xylem vessels are continuous hollow tubes. Tracheids are elongated cells with tapering ends. Function To transport water and mineral salts. Supporting tissue. Vascular tissue Sieve tubes are To translocate organic elongated and products of tubular, consisting of photosynthesis. phloem elements Companion cells closely Companion cells are associated with sieve smaller, with dense tubes. cytoplasm. THE END 9

2.5 : Cells are grouped into tissue

2.5 : Cells are grouped into tissue 1 CELL STRUCTURE AND FUNCTIONS Prokaryotic and eukaryotic cells Structures & functions: Cell membrane and organelles Animal Cells are grouped into tissue Plant Cell