Plant Biology Lecture Notes PDF

BIO 2203. PL ANT BIOLOGY Assist. Prof. Dr. Aydan ACAR ŞAHİN [email protected] 4.10.2024 Biology is the study of complicated things that have the appearance of having been designed...

BIO 2203. PL ANT BIOLOGY Assist. Prof. Dr. Aydan ACAR ŞAHİN [email protected] 4.10.2024 Biology is the study of complicated things that have the appearance of having been designed with a purpose… Richard Dawkins. TODAY…OUTLINE What is histology? What is the main difference between the real and pseudo tissues? The importance of intercellular spaces system, formation mechanism and types Cell wall, pits and their properties Classification of plant tissues? What is meristem? What are the permanent tissue types? Different types of simple permanent tissue (Parenchyma and Collenchyma) Functions of different parenchyma tissues. What is the main differences between parenchyma and collenchyma tissues?  LEARNING OBJECTIVES: ❖ The Importance of Meristematic cell and their types ❖ What is The Main Difference Between The Meristematic and Permanent Tissues? ❖ Distinguish the plant tissue types, their structures and their functions ❖ Distinguish the types of parenchyma due to their functions ❖ Distinguish the differences between parenchyma and collenchyma tissues “STRUCTURE CORRELATES TO FUNCTION”  Plant histology Histology – (Histos = tissue + logos = study). A plant tissue can be defined as a cell or a group of cells dividing, to give rise to large number of cell, which is collectively referred as tissues. They are structurally and functionally similar to these cells. Histology is the study of tissues and cells under a microscope. Histology is obviously related to Cell Biology (Cytology) and to Anatomy; it also forms the structural basis for understanding function (physiology) and is the preparation for the study of abnormal or normal structure and function. Tissue produce organs. Plants do have a higher level of structure called plant tissue systems. A plant tissue system can be defined as a functional unit, which connects all organs of a plant.  HISTOLOGY The tissue occurs as a result of cell division. While, dividing cells in unicellular organism constitute a new members separated from one another, dividing cells in multicellular organisms, together with a new cell wall are formed adjacent to each other. These membranes have passageways (pits) and protoplasmic structures called plasmadesmata, which pass matter and stimulus between two protoplasms through these passages. This is how the adjacent cell groups formed a tight relationship between the protoplasts occur tissues. In some primitive plant groups, in particular cells which are united independently combine together and give subsequently side view of a tissue. For example; Pediastrum ve Gloeocapsa. There is no cytoplasmic relationship between these cells. This is called a pseudo-tissue or cell colony. Pediastrum  The basic shape and relationships of plant cells and Intercellular Spaces As the cell expands in volume in the meristematic area, the primer cell wall takes on the shape of the lowest surface. So after mitosis, the pups want to get a shape close to the spherical shape. But there is no intercellular space between intensely co-existing cells. The cell therefore has a very superficial shape. The base of the cell is a 14-faced polyhedron. The number of faces can be 12-16 or more. The surfaces are pentagonal. But they can also be tetragonal and hexagonal. We can see something similar in soap bubbles. The increase in cell volume during growth leads to a further increase in cell surface. This makes it impossible for all surfaces to become contact with the surfaces of neighboring cells. Therefore, the intercellular space system starts to form. In some tissues, intercellular spaces reach very large sizes and form air gaps and secretory channels.. FUNCTIONS OF INTERCELLULAR SPACES Through Intercellular space; 1. The air entering the tissues on the inside of the plant, whether it is in plants, in water or on land, from stomata and similar organs, is reached via this system. In the internal tissues, carbon dioxide, water vapor and other gases, which result in physiological activities, are thrown out of the plant in this way. So, they provide gas exchange for the internal parts of the plant. 2. The spaces are exceptionally well developed in aerenchyma of many aquatic plants. They form a connected system throughout the entire plant body. The spaces may be vertical and are filled with air and water, thus forming air spaces and air canals. Air spaces and air canals help in aeration and add buoyancy to plant. It has been suggested that, the honeycomb-like system of intercellular spaces in aquatic plants can withstand considerable mechanical stress. 3. In terrestrial plants, the enlarged intercellular space gives rise to secretory glands (ex. Citrus sp.) or ducts (ex. Pinus). Based on the mode of formation, four types of intercellular spaces are distinguished: 1. Schizogenous intercellular spaces, The most common intercellular spaces result from separation of cell walls from each other along more or less extended areas of their contact. The resin ducts in the Coniferales, and the secretory ducts in the Compositae and Umbelliferae are the typical examples. 2. Lysigenous intercellular spaces, This type of intercellular space arises through dissolution of entire cells, which are therefore called lysigenous intercellular spaces. Citrus and Gossypium are good examples. These cavities of intercellular spaces store up water, gases and essential oils in them 3. Schizo- Lysigenous intercellular spaces, Sometimes intercellular spaces of mixed origin develop, which, having been formed schizogenously, enlarge rhexigenically or lysigenously. Schizo- Lysigenous intercellular has features between Schizogenous and Lysigenous intercellular spaces. For example protoxsilem cavity (Closed-collateral vascular bundle). 4. Rhexigenic intercellular spaces. Rhexigenic intercellular spaces, result from the rupture, or rhexis, and subsequent atrophy of cells. The large cavities in the internodes of stems in many Gramineae and Labiatae are formed by cellular rhexis. For example: Triticum (Wheat) QUİZ….??? 1. Which type of intercellular spaces are seen in this figure? 2. ……..is the study of tissues under a microscope. A. Morphology B. Cytology C. Organographies D. Histology 3. What is a tissue? A. group of cells that share a common goal B. a tissue that has a function C. a group of cells that share a common function, structure or both D. a group of cells ANSWERS 1. Citrus sinensis (orange)- Lysigenous intercellular spaces 2. Histology 3. a group of cells that share a common function, structure or both  THE CELL WALL ✓ One of the most distinctive structural features of plant cells is the surrounding wall, characteristically composed of the carbohydrate present only in plant cells cellulose deposited in fibrillar form. non-protoplasmic ✓ The cell wall is widely considered to be a nonliving entity or considered as metabolic by secretion of the protoplast that further protects and supports the protoplast while strengthening the cell and tissue to which it product of the protoplast belongs. provides support and protection to cell ✓ Cell walls provide rigidity and define cell shape. They must be strong enough to maintain turgor pressure, yet they must also plays an important role in possess properties capable of permitting cell expansion. absorption, translocation and secretion ✓ The wall is a dynamic structure that grows and has the ability to alter both its shape and composition. ✓ Cell walls play important roles in plant development, cell-to-cell communication, physiology, and environmental adaptation and stress responses  THE CELL WALL Composed of different layers: 1. The Cell Plate and Middle Lamella The cell wall first becomes visible as a cell plate that arises during late telophase of mitosis. Each cell has its own middle lamella. The cell wall of the adjacent cells is joined by middle lamella. Middle lamella is a thin layer. Cellulose is absent in it. It is mainly composed of pectic compounds and can be dissolved by applying certain chemicals. It separates the cells. This process is called maceration. Middle lamella acts as an intercellular substance and holds the cell together. Chromosomes are attracted to the poles. Pectic substances are synthesized by the dictyosomes (Golgi apparati) and transported to the cell plate in vesicles, the cell plate is transformed into the middle lamella. it is finally middle lamellar formation at the end of telophase stage 2. The Primary Wall The primary wall is optically anisotropic, meaning that its wall materials have unequal optical properties along different axes. It is the first visible layer of the cell wall, and its formation accompanies extension growth. It develops on either side of the middle lamella when two cells are adjacent and largely determines cell shape and size during plant growth and development. It is composed of a continuous interconnected, fortifying system of aggregated, threadlike cellulosic microfibrils that result from the simultaneous polymerization and crystallization of cellulose molecules. 3.The Secondary Wall The secondary wall is very thick and also are strongly anisotropic. In cells like the gymnospermous secondary xylem water-conducting tracheid, they are microscopically layered, consisting of a relatively narrow outer layer (S1), a middle layer of variable width (S2), and narrow inner layer (S3). The three layers are characterized by a different fibril angle of orientation of the abundant and extremely long cellulose microfibrils.  WALL PITS They act as the channels for the transport of water and minerals between adjacent cells. Pits of two neighboring cells are usually located opposite to each other and these opposite pits together are called pit pair. Each pit has a cavity called pit cavity. Pit cavity opens internally to the lumen of the cells. Wall pits Bordered Half Simple pits pits bordered pits SIMPLE PITS Pits which lack the borders are called simple pits. Two opposite simple pits are called simple pit pair. Simple pits are usually present in parenchyma cells and Sclereid cells.  BORDERED PITS During the development of pits, the secondary cell wall may over arch the pit cavity forming a border, leaving an inner opening called pit-aperture. Such pits with borders are called bordered pits. Two opposite bordered pit are called bordered pit pair. It is found in lignified fibres, opposite between tracheary cells (trachea or tracheid). The middle of the pit membrane forms a circular thickening structure called torus. Torus is larger in diameter than the pit aperture and is composed of primary cell wall materials. The remaining part of the pit membrane surrounding the torus is called margo. Margo is flexible and thin. Under certain circumstances, the margo moves towards one or the other pit aperture closing the same with the torus pit aperture In tracheary cells, the bordered pits are arranged in three characteristic patterns: (1). Scalariform pitting: If pits are elongate and are arranged in a ladder like series (2). Opposite pitting: Pits are arranged in horizontal rows or pairs. In opposite pitting, the pits are so closely placed and hence the outline of the pits become rectangular in surface view (3). Alternate pitting: Pits are arranged in diagonal rows, in alternate pitting, the pits are so closely placed and hence the outline of the pits become hexagonal  HALF BORDERED PITS When a bordered pit is opposed by a simple pit. It is found to opposite between parenchyma cell and tracheid or trachea cells. Bordered pits Half Bordered pits Simple pits  Differences between simple pits and bordered pits summary Simple Pits Bordered Pits Simple pits occurs mainly in parenchymatous cells and rarely in 1 Occurs in trache, tracheid cells only. Absent in parenchymatous cells sclerenchymatous cells Found in medullary rays, extra-xylary fibres, companion cells and Abundantly found in vessels of angiosperms and tracheids of gymnosperms 2 in tracheids of some angiosperms and ferns 3 Pit cavity remains in the same diameter throughout Size and shape of pit cavity varies 4 Closing membrane of pit remain in same diameter throughout Closing membrane of pit varies in their diameter during development 5 Simple organization of pit membrane Pit membrane with complex organization 6 Pit border absent Pit border present, formed by the overarching of secondary cell wall 7 Pit aperture absent Pit aperture present, formed due to presence of pit borders Pits may be circular, oval, polygonal, elongated or irregular in facial 8 Pit aperture may be circular, linear or oval in facial view view Simple pits occurring in the thin walls are shallow where as in In the case of thick secondary wall, the border divides the cavity into two thick wall the pit cavity may have the form of a canal passing from parts- the space between the closing membrane and the pit aperture is 9 the lumen of the cell towards the closing or common pit called pit chamber, and the canal leading form pit chamber to the lumen of membrane the cell is called pit canal Pit membrane homogenous or heterogenous. Homogenous in angiosperms 10 Pit membrane homogenous and heterogenous in gymnosperms Torus is present ,torus is the thickening of pit membrane which act as 11 Torus is absent valves Torus and margo together with pith aperture acts like valves and which 12 Valve like opening and closing mechanism absent regulate the opening and closing of pits 13 Plasmodesmatal connections are seen in pit membrane Plasmodesmatal connections are absent in the pit membrane PLANT TISSUES  PLANT TISSUES Plant tissues are broadly classified into two categories based on their capacity of cell division.: (1) Meristematic tissues (2) Permanent tissues. Meristem is a type of tissue system in plants, composed of a mass of undifferentiated cells and their primary function is to take part in the growth of plants. Permanent tissues are differentiated tissues doing specific functions such as conduction, providing mechanical support or carrying out photosynthesis etc. Permanent tissues are originated and differentiated from meristematic tissues!!  MERISTEMATIC TISSUE Meristematic tissue is group of immature cells that has capacity of division and redivision. The term meristem was coined by Nageli (1858). Meristems in plants are found in apex of stem, root, leaf primordia, vascular cambium, cork cambium, etc. Meristems are continuously dividing tissues of the plant. They are responsible for primary (elongation) and secondary (thickness) growth of the plant. Secondary tissues such as, cork, wood are also occured due to activity of meristematic tissue. They are small and tightly packed with small vacuoles, rudimentary chloroplasts, and thin cell walls. CHARACTERİSTİCS OF MERİSTEMATİC CELL  Meristems are divided into two types criterions: 1. Classification based on position in the plant body: - Apical meristem - Lateral meristem -Intercalary meristem 2. Classification based on nature of cell giving the meristem: - Primary meristem - Secondary meristem  1. Classification based on position in the plant body 1. APİCAL MERİSTEM Apical meristems are found at tip of stem, roots and leaves. They are also called as APICAL CELL or apical initial. The activity of apical meristem causes increase in the length of shoot and root. Apical meristem produces the primary structure of plants. Shoot apex Root apex  APICAL MERISTEM-SHOOT APEX The tissue zones of shoot apex are: Protoderm: give rise to epidermis Procambium: give rise to primary vascular tissue (xylem & phloem) Ground meristem (fundamental meristem): give rise endodermis, pericycle, cortex, medulla and pith  APİCAL MERİSTEMS –SHOOT APEX: There are many theories have been put forward to explain the shoot apex FOR ANGIOSPERMS (NAGELİ, 1858) THE TUNİCA-CORPUS THEORY (SCHMİDT, 1924) THE TUNİCA-CORPUS THEORY  FOR GYMNOSPERM_SHOOT APEX ❖ Gymnosperm meristems do not have distinct tunica layers and are better described by apical meristematic zones. ❖ The major zones include: Apical initials Central mother cells, Rib meristem, Surface layer cells, Peripheral zone. Recent cytohistological studies indicate that the gymnosperm shoot apex contains a complicated arrangement of groups of cells which are characterised by their size and nucleus, differential staining pat- tern, relative wall thickness, and the frequency and orientation of the plane of cell division. Cycas type Ginkgo type Crytptomeria-Abies type  Based On The Structure And Development, Popham (1952) Distinguished Three Main Types of Gymnosperm Shoot Apex: 1. Cycas Type: In Cycas type (See above figure) there are three meristematic zones: (a) The Surface Meristem: The cells of this meristematic zone divide anticlinally, periclinally and diagonally. They are not uniform in size and the apical initials are distinguished in the centre of this zone in the seedling stage. Epidermis and other meristematic regions arise from this zone. (b) The Rib Meristem: This meristem is situated centrally in the apex below the surface layer. Cells of this meristem are arranged in vertical rows. They divide periclinally, anticlinally and diagonally near the base. Pith develops from this zone. (c) The Peripheral Meristem: The cells of this meristem are elongated. Cell division takes place within the zone itself. Further addition of cells to this zone takes place from the surface layer and from the periphery of the rib meristem. The derived cells of this zone differentiate into the cortex, the procambium and the leaf primordia. 2. Ginkgo Type: In Ginkgo type, there are five meristematic zones as: (a) The Surface Meristem: This zone remains at the summit of the apex. Cells of this zone are large, polyhedral and irregularly arranged; they divide in various planes. (b) The Zone of Central Mother Cells: Beneath the surface meristem this zone is located centrally. (c) The Rib Meristem: Just beneath the cambium like transitional zone the rib meristem is distinguished. The cells of these zones are usually arranged in rows. From this meristem, pith of the stem develops. (d) The Peripheral Meristem: The peripheral meristem forms a cylinder surrounding the rib meristem and is a continuation of the cambium-like transitional zone. In this zone, the number of cells increases by division in the meristem itself as well as by the addition of cells from the surface meristem and the cambium-like transitional zone. (e) The Cambium-Like Transitional Zone: The cambium-like transitional zone is cup-shaped, relatively narrow and characterized by frequent cell divisions. This zone forms a transitional zone between the central mother cells and the rib and flank meristems. Most of the divisions are periclinal in relation to the central mother cells. So the cells are added to the zones below it. The cortex, leaf primordia, procambium and in some cases the outer region of the pith develop from this zone. 3. The Cryptomeria-Abies Type: In this type four meristematic zones are distinguished. Excepting the cambium-like transitional zone all other zones are remaining same like that of Ginkgo type. In Pinus montana, Sequoia, Metasequoia glyptostroboides, Abies concolor, Taxus baccata, Ephedra altissima and Cryptomeria japonica. This type shoot apex is found.  2. Intercalary Meristem Ø They are not typical meristems since these cells later completely differentiated into permanent tissues. Ø They are the cells with meristematic activity present between permanent tissue regions in the plant. Ø They are portions of apical meristem that were separated from the apex during development by layers of differentiated tissues. Ø Regions with intercalary meristems are the actively growing region behind apical meristem. Ø Intercalary meristem is commonly found in internodes of vascular plants. They also occur in leaf sheath of some grasses. Ø In Equisetum (a primitive Pteridophyte) intercalary meristem is present just above the node.  3. Lateral Meristem Ø Lateral meristems are the meristematic tissue present parallel to the organs in which they occur. Ø They help in increasing diameter of the plant body by adding new cells to the existing tissues. Ø They divide only in one plane. Ø Example: Vascular cambium and Cork cambium (phellogen)  SUMMARY Apical meristem is present on root and shoot tips of the plant. This tissue divides and results in growth of stem and roots of the plant. Intercalary meristem is present on leaf base and nodes. Lateral meristem is responsible for increase in circumference i.e. girth of the stem or root of the plant. https://learnfatafat.com/meristematic-tissue 2. Classification based on nature of cell giving the meristem:  QUİZ….??? 1. Compared to primary cell walls, secondary cell walls are typically… a. thicker. b. stronger. c. less active. d. more lignified. e. all of the above. 3. Which tissue gives rise to secondary growth? a. apical meristem. b. adventitious roots. c. germinating seed. d. terminal buds. e. vascular cambium. 1-2:E  PERMANENT TISSUES Evolutionary history of plants ❖ more hours of light, ❖ more light intensity, ❖ more free movement of CO2 In return, plants had to solve new challenges, most of them related to obtaining and retaining water, keep an erect body, as well as the dispersion of seeds in the air  -SIMPLE TISSUES- 1.PARENCHYMA The term parenchyma (Para means “beside” and chyma means “infilling”) was first introduced by Nehemiah Grew (1682). They are a simple permanent tissue. They have living cells. They are found in the cortex, pith of roots and stems, mesophyll of leaves, succulent roots, endosperm. Parenchyma cells are generally polyhedral in shape.. Parenchyma cells usually have thin primary walls and simple pits.  From the evolutionary point of view, the parenchymatic cell is regarded as the ancestor or precursor of the other cell types of the plant because it is not much differentiated and shows similar behavior as meristematic cells. For example, it can dedifferentiate by decreasing the thickness of the cell wall, and becomes a totipotent cell that can proliferate. Thus, parenchyma is an excellent source to produce callus (in vitro mass of undifferentiated cells that proliferate and differentiate to give an adult plant) Shape and arrangement Parenchyma cells are generally polyhedral i.e. with many sides. Even if the parenchyma cells are approximately isodiametric, they are not spherical but have many facets. Plant cells rarely approach this ideal from because inside the tissue the pressure exerted is uneven. Parenchyma cells may be elongated columnar in shape as found in palisade tissue of the leaf. Stems of plants shows well-developed air spaces (Scirpus, petiole of Canna leaf) with their stretched arms, such parenchymatous cells are called stellate parenchyma. Parenchyma cells can be variously lobed e.g. spongy mesophyll and palisade parenchyma of Helium and Pinus needle. B C A Figure: A) Transverse section of leaf of cattail (Typha) leaf showing stellate parenchyma. B) T.S. of needle leaf of pine (Pinus) showing presence of lobed parenchyma cells (all the red-stained cells). 1. SYNTHETIC PARENCHYMA It is generaly found in the mesophyll tissues of leaves. Mesophyll tissue is differentiated into compactly arranged columnar cells called as palisade and loosely arranged tissue called spongy parenchyma. These are chlorophyll containing cells so known as chlorenchyma. Palisade parenchyma Spongy parenchyma 2. AERENCHYMA Nymphaea leaf  A B C D Figure: A) T.S. of Nymphaea leaf showing aerenchyma tissue; B) T.S. stem of Myriophyllum showing aerenchyma cells in the cortex region; C) T.S. of adventitious roots of (a) rice and (b) maize taken 50 mm from the root apex and showing lysigenous aerenchyma formation. Note the cubic cell packing in the rice cortex contrasting with the hexagonal packing in maize  3. T R A NSP O RT PA R ENCH Y MA The parenchymatous cells in xylem or phloem is meant for the transportation of water, minerals and food particles are called as transport parenchyma. Figure: T. S. stem of Cucurbita pepo showing primary xylem and phloem (the arrow indicates a sieve plate). Transfer cells with wall ingrowths called a labyrinth. In a variety of tissues where transport of solutes over short distances i.e. active transport or facilitated transport is required, surface area including cell membrane increases by wall ingrowths e.g. haustorial cells in parasitic plants such as Cuscuta. Figure: Cuscuta campestris: haustorium penetrating host tissues. 4. STORAGE PARENCHYMA Reserve materials are stored in the cytoplasm and vacuoles of storage parenchyma cells in form of fluid (amides and proteins) or in the form of small solid particles (starch, proteins, oils, fats) or liquid. Cotyledonary cells of legumes show proteins and starch grains in the cytoplasm. Parenchyma cells may be involved in the storage of water as in succulent plants as like cactus or arid plants. in Opuntia ficus-indica in Solanum tuberosum Water Storage parenchyma Food Storage parenchyma  A) B) C) Figure: Parenchyma cell including A) chloroplast and B) chromoplasts C) starch grains (bean cotyledons) Properties of collenchyma Cell wall of collenchyma in addition to cellulose contains large amounts of pectin and hemicelluloses without lignin deposition. Presence of pectin makes them hydrophilic and helps in retaining much water. Ultrastructural detail shows presence of cross poly lamellate or helicoidal structure in collenchyma wall with primary pit fields. Collenchyma cells are known to possess several pattern in their wall thickening which can be seen either in the corners of the cell, inner and outer tangential wall or on two opposite wall. Figure: Collenchyma cell A) transverse section B) longitudinal section. THERE ARE FOUR TYPES OF COLLENCHYMA ON THE BASİS OF NATURE OF WALL THİCKENİNG ARRANGEMENT OF CELLS:  A. ANGULAR COLLENCHYMA Thickening materials deposited only at the corners of the cells and found under the epidermis. Figure: Angular collenchyma in Celery petiole It can be seen in the stem of Atropa belladonna, Solanum tuberosum and petiole of Begonia, Beta, Coleus, Cucurbita, Morus, Ricinus Vitis, Cannabis and Celery (Apium graveolens).  B. LAMELLAR COLLENCHYMA *Wall thickening is resticted to tangential walls of the cells  C. LACUNAR COLLENCHYMA Wall thickening is restricted around the intercellular spaces. D. ANNULAR COLLENCHYMA  Parenchyma vs Collenchyma Similarities and Differences between Parenchyma and Collenchyma Similarities between Parenchyma and Collenchyma ✓ Both parenchyma and collenchyma are simple permanent tissues in the plants. ✓ Both are differentiated cells. ✓ Both are living cells with primary cell wall. ✓ Both cells possess cytoplasm and cell organelles including the nucleus. ✓ Both are the components of ground tissue system in plants. ✓ Both cells can do photosynthesis if chloroplasts are present in them. ✓ Both can store food materials as starch grains. ✓ Pits are absent in the cell wall of both parenchyma and collenchyma. ✓ Plasmodesmatal connections between cells occur in both cells. Differences Between Parenchyma and Collenchyma Parenchyma Collenchyma 1 Cells with thin cell wall. Cell wall is thick. 2 Cell wall made up of cellulose. Cell wall made of cellulose and pectin. Deposition of cellulose and pectin is uneven in the cell wall. Wall thickening is 3 Deposition of cellulose is even in the cell wall. more in the corners of the cells. 4 Cells are usually loosely arranged with intercellular spaces. Cells are usually closely packed without intercellular spaces. 5 Parenchyma is present in all parts of the plant body. Usually present below the epidermis of the plant as hypodermis. 6 Secondary thickening absent. Secondary thickening present. 7 Cells usually isodiametric to circular in shape. Cells usually polygonal in shape. 8 Cells can store waste products, tannins, gums, resins etc. Usually cells do not store any waste products or ergastic substances. Can provide mechanical support even in the flaccid condition due to the thick 9 Can provide mechanical support only when the cells are fully turgid. cell wall. 10 Present in both in the primary and secondary structures of the plants. Usually present only in the primary structures of the plants. 11 Present in both xylem and phloem as one component. Collenchyma is not found in xylem and phloem. Parenchymatous cells undergo several modifications such as 12 Collenchymatous cells do not show such modifications. chlorenchyma, aerenchyma, palisade, spongy etc.. Cells can be dedifferentiated into meristematic cells (example: formation 13 The ability of dedifferentiation is literally absent in collenchyma. of vascular cambium and phellogen during secondary growth). Functions of Parenchyma: Functions of Collenchyma: (a). Store water (a). Provide mechanical support (b). Store food materials (starch) (b). Provide flexibility to petiole, leaves etc. 14 (c). Chlorenchyma can assist in photosynthesis (c). Facilitate bending of the plant organ without breaking (d). Aerenchyma can provide buoyancy (d). Collenchyma can also store food materials (e). Store ergastic substances (e). Can perform photosynthesis if chlorophyll is present (f). Can provide meristematic tissue  QUİZ….??? 1. Totipotency is the ability of a cell to a. undergo metabolism. b. undergo mitosis. c. differentiate into any cell type. d. die at maturity. e. secrete cell wall material. 2. which of the following is a function of the parenchyma tissue? a. photosynthesis b. storage c. Provides buoyancy d. wound repair e. all of above QUİZ….??? 3. Which type of collenchyma is seen in this figüre? 4. Cell walls of collenchyma cells are flexible due to…. a. a high lignin content. b. their elastic nature due to contractile proteins. c. irregular secondary thickenings. d. a helicoidal arrangement of cellulose microfibrils. e. layers that slide past one another ANSWERS 1C 2E 3 angular collenchyma 4B  Difference between Meristematic Tissues and Permanent tissues: Meristematic Tissues: (1). Meristematic tissue composed of undifferentiated cells (2). Meristems will be always a simple tissue, composed of only one type of cells (3). Cells are always living (4). Cells always contain dense cytoplasm KEY POINTS (5). Cells always contain prominent nucleus (6). Cells divide very rapidly (7). Cells are smaller and isodiametric in shape with large lumen (8). Cells are compactly packed without inter-cellular spaces SUMMARY (9). Cells usually lack vacuoles (10). Cells show very high rate of metabolism (11). Cell wall very thin and cellulosic (12). Cells do not undergo secondary thickening (13). Lignified secondary cell wall completely absent (14). Cells only contain primary pit fields (15). Cellular inclusion and ergastic substances completely absent in the cells (16). Cells do not store reserve food materials (17). Meristematic tissues produce permanent tissues (18). Meristematic tissues are restricted to certain parts of plant body (19). Example: Root apex, Shoot apex (20). Primary function of meristem is to assist in plant growth Permanent Tissues: (1). Permanent tissue composed of differentiated cells (2). Permanent tissues may be simple tissue or complex tissues (usually complex tissue, containing more than one type of cells, example: xylem, phloem) (3). Cells may be living (Parenchyma and Collenchyma) or non-living (Sclerenchyma) (4). Cells may or may not contain cytoplasm (Parenchyma contain cytoplasm, Sclerenchyma do not contain cytoplasm) (5). Prominent nucleus present in some cells (Parenchyma) absent in others (Sclerenchyma) (6). Cells do not divide, they are completely differentiated (7). Cells are larger, varying in shape with very wide or very narrow lumen KEY POINTS (8). Cells loosely packed in parenchyma and compactly packed in sclerenchyma (9). Living cells are vacuolated but dead cells are devoid of protoplasm (10). Metabolic rate usually very less or no metabolism at all (11). Cell wall cellulosic (Parenchyma and Collenchyma) or lignified (Sclerenchyma) SUMMARY (12). Cells may or may not undergo secondary thickening (13). Lignified secondary cell wall sometimes present (as in Sclerenchyma) (14). Cells usually contain many advanced types of pits (15). Ergastic substances and cellular inclusion usually present (16). Some cells store reserve food materials such as starch (17). Permanent tissues are derived from meristematic tissues (18). Permanent tissue are found throughout the plant body. Example: Xylem, Phloem, Mesophyll (19). Primary function varies with tissue types. It may be conduction, provide mechanical support, or carry out photosynthesis