Cell Biology of Plants PDF - MSCBOT-506

MSCBOT-506 M.Sc. II Semester CELL BIOLOGY OF PLANTS DEPARTMENT OF BOTANY SCHOOL OF SCIENCES UTTARAKHAND OPEN UNIVERSITY CELL BIOLOGY OF PLANTS MSCBOT-506...

MSCBOT-506 M.Sc. II Semester CELL BIOLOGY OF PLANTS DEPARTMENT OF BOTANY SCHOOL OF SCIENCES UTTARAKHAND OPEN UNIVERSITY CELL BIOLOGY OF PLANTS MSCBOT-506 MSCBOT-506 CELL BIOLOGY OF PLANTS DEPARTMENT OF BOTANY SCHOOL OF SCIENCES UTTARAKHAND OPEN UNIVERSITY Phone No. 05946-261122, 261123 Toll free No. 18001804025 Fax No. 05946-264232, E. mail [email protected] htpp://uou.ac.in UTTARAKHAND OPEN UNIVERSITY Page 1 CELL BIOLOGY OF PLANTS MSCBOT-506 Expert Committee Prof. J. C. Ghildiyal Prof. G.S. Rajwar Retired Principal Principal Government PG College Government PG College Karnprayag Augustmuni Prof. Lalit Tewari Dr. Hemant Kandpal Department of Botany School of Health Science DSB Campus, Uttarakhand Open University Kumaun University, Nainital Haldwani Dr. Pooja Juyal Department of Botany School of Sciences Uttarakhand Open University, Haldwani Board of Studies Late Prof. S. C. Tewari Prof. Uma Palni Department of Botany Department of Botany HNB Garhwal University, Retired, DSB Campus, Srinagar Kumoun University, Nainital Dr. R.S. Rawal Dr. H.C. Joshi Scientist, GB Pant National Institute of Department of Environmental Science Himalayan Environment & Sustainable School of Sciences Development, Almora Uttarakhand Open University, Haldwani Dr. Pooja Juyal Department of Botany School of Sciences Uttarakhand Open University, Haldwani Programme Coordinator Dr. S.N.Ojha Assistant Professor Department of Botany, School of Sciences Uttarakhand Open University, Haldwani, Nainital UTTARAKHAND OPEN UNIVERSITY Page 2 CELL BIOLOGY OF PLANTS MSCBOT-506 Unit Written By: Unit No. 1. Dr. Kirtika Padalia 1 Assistant Professor Department of Botany Uttarakhand Open University, Haldwani 2- Dr. Arun Joshi 2 Assistant Professor, Department of Botany SGRR PG College, Dehradun 3. Dr. Shalabh Gupta 3 Associate Professor, Department of Botany SBS Government Post Graduate College, Rudrapur 4. Dr Gyanendra Awasthi 4, 5, 6 & 7 Associate Professor Department of Biochemistry Dolphin Institute of Biomedical & Natural Sciences Dehradun 5. Dr. Narendra Kumar 8, 9 & 10 Assistant Professor Department of Botany M. B. Govt. P. G. College, Haldwani Chief Course Editor Prof. R.C. Dubey Head, Department of Botany & Microbiology Gurukul Kangri University, Haridwar Editorial Board Dr. Pooja Juyal Dr. S.N. Ojha Department of Botany Assistant Professor, Department of Botany School of Sciences School of Sciences Uttarakhand Open University, Haldwani, Uttarakhand Open University, Haldwani Dr. Kirtika Padalia Dr. Prabha Dhondiyal Assistant Professor (AC) Assistant Professor (AC) UTTARAKHAND OPEN UNIVERSITY Page 3 CELL BIOLOGY OF PLANTS MSCBOT-506 Department of Botany, School of Sciences, Department of Botany, School of Sciences Uttarakhand Open University, Haldwani Uttarakhand Open University, Haldwani Dr. Pushpesh Joshi Assistant Professor (AC) Department of Botany, School of Sciences Uttarakhand Open University, Haldwani Title : Cell Biology of Plants ISBN No. : Copyright : Uttarakhand Open University Edition : 2022 Published By: Uttarakhand Open University, Haldwani, Nainital-263139 UTTARAKHAND OPEN UNIVERSITY Page 4 CELL BIOLOGY OF PLANTS MSCBOT-506 CONTENTS BLOCK-1 PLANT CELL PAGE NO. Unit-1 Prokaryotic and Eukaryotic 7-44 Unit-2 Cell Division 45-59 Unit-3 Cell Senescence 60-72 BLOCK-2 EXTRANUCLEAR ORGANELLES PAGE NO. Unit-4 Cell Wall 74-101 Unit-5 Mitochondria 102-122 Unit-6 Chloroplast and Endoplasmic Reticulum 123-150 Unit-7 Ribosome and Golgi apparatus 151-192 BLOCK-3 INTRANUCLEAR ORGANELLES PAGE NO. Unit-8 Nucleus 194-203 Unit-9 Chromosomes 204-223 Unit-10 Cell signaling and Cell receptors 224-243 UTTARAKHAND OPEN UNIVERSITY Page 5 CELL BIOLOGY OF PLANTS MSCBOT-506 BLOCK-1 PLANT CELL UTTARAKHAND OPEN UNIVERSITY Page 6 CELL BIOLOGY OF PLANTS MSCBOT-506 UNIT-1 PROKARYOTIC AND EUKARYOTIC Contents 1.1 Objectives 1.2 Introduction 1.3 Structure and organization of cells 1.3.1 Prokaryotic cells 1.3.2 Eukaryotic cells 1.3.2.1 Shape 1.3.2.2 Size 1.3.2.3 Number 1.3.2.4 Structure 1.4 Specialized plant cell types 1.4.1 Cells of the ground tissue system 1.4.2 Cells of the dermal system 1.4.3 Cells of the vascular system 1.5 Chemical composition of cell 1.5.1 Inorganic compounds 1.5.2 Organic compounds 1.5.1.1 Carbohydrates 1.5.1.2 Lipids 1.5.1.3 Protein 1.5.1.4 Nucleic acids 1.6 Summary 1.7 Glossary 1.8 Self assessment questions 1.8.1 Multiple choice questions 1.8.2 Fill in the blanks 1.8.3 True and False 1.9 References 1.10 Suggested readings 1.11 Terminal questions 1.11.1 Short answer type questions 1.11.2 Long answer type question UTTARAKHAND OPEN UNIVERSITY Page 7 CELL BIOLOGY OF PLANTS MSCBOT-506 1.1 OBJECTIVES The present topic provides an overview of structure, organization and chemical composition of the prokaryotic as well as eukaryotic organisms. After reading this topic you will learn about the following:  Fundamental characteristics of prokaryotic and eukaryotic organisms.  Able to differentiate between prokaryotic and eukaryotic organisms  Cell structure and organization of organisms  Know about cellular structure of plant and animal cell  Specialized plant cell types  Chemical composition of cell 1.2 INTRODUCTION Cell "building blocks of life" is the smallest unit of all organisms. The cell was first discovered by Robert Hooke in 1665 after building of the microscope. The word cell is derived from a Latin word ―cella” which means small room. Cell is considered as basic biological, structural and functional unit of all living organisms. Cells consist of cytoplasm enclosed within a membrane, which contain many vital macromolecules such as proteins and nucleic acids. The cell is a unit of biological activity delimited by a semipermeable membrane and capable of self-reproduction in a medium free of other living systems. However, this definition is not applicable for the viruses because they are capable to self-multiply only using the cellular machinery of other organisms. All the living organisms, except virus and certain group of plants (Rhizopus, Vaucheria etc.) possess the well-organized cellular body which may contain one or more cells. According to the number of cells, the organisms can be divided into two categories. The living organisms which are made up of a single cell are known as unicellular organisms. All blue green algae, some higher algae (diatoms, Cosmarium, Chlorella, Microcystis, Pinnularia, Haematococcus etc.) and group of protozoa are the good examples of unicellular organisms. On the other hand, the organisms made up of more than one cell is called multicellular (other group of plants and animals). The cells are found in different varieties of shapes, sizes and numbers which indicate their evolutionary adaptation at different environmental conditions. Cells range in size from the smallest bacteria, only a few tenths of µm in diameter to certain large marine algae and to various bird eggs with dimension of centimeters. Besides all its apparent diversity, however, cells have many common characteristics, for example, potential for an independent existence. Thus cells have the ability to continue living in the absence of any other cell. In the same reference, the cell theory explains that all living organisms are constructed by one or more cells, UTTARAKHAND OPEN UNIVERSITY Page 8 CELL BIOLOGY OF PLANTS MSCBOT-506 and the functions of a multicellular organism are a consequence of the types of cells it has. According to this theory, each living beings on this earth begin its life as a single cell. Some living being, including bacteria, remain single-celled in the process of evaluation, while the other living things (including plants and animals) grow and develop into many cells. Collectively, all the living cells are broadly classified into two category i.e., prokaryotic cells and eukaryotic cells, according to whether their genetic materials are enclosed by a nuclear envelope or not. Eukaryotic cells possess this envelope while a prokaryotic cell does not. Eukaryotic cells may have evolved from prokaryotic cells but contain different types of organelles like well-organized nucleus, endoplasmic reticulum, golgi body, mitochondria etc, which are specific in their functions. But features like growth, response, and most importantly giving birth to the young ones are the commonly shared by all living organisms. 1.3 STRUCTURE AND ORGANIZATION OF CELLS Life exhibits varying degrees of organization. Based upon the origin and development, cells fall into two major groups: prokaryotes and eukaryotes. The term prokaryotic and eukaryotic were coined by Hans Ris in the early 1960‘s. Any cellular organism may have only one kind of cell either prokaryotic or eukaryotic. Prokaryotic cells are usually more primitive, smaller, simple, and lack the internal compartmentalization while eukaryotic cells have a great variety of organelles and have internal organization. No matter, which type of cell we are considering; all cells have certain features in common, such as a cell membrane, genetic material, cytoplasm, and ribosomes. 1.3.1 Prokaryotic cells Prokaryotic cells may be defined as the cells which do not have a true nucleus and the membrane-bound organelles. Organisms that possess such kind of cells are known as prokaryotes and they are typically unicellular in organization (Nelson and Cox 2005). For example: Archaea, bacteria, pleuropneumonia like organisms (PPLO), blue green algae, protozoa etc. The prokaryotic (Gr., pro- primitive, karyon- nucleus) cells are the most primitive type of cells that exist on this earth from the morphological point of view. These are the simplest and mostly small sized (1-10 µm) cells. It is essentially one envelope system. As its name indicates, the nucleus are primitive type but true nucleus is absent. The cells comprise of a central nuclear components, sometime called nucleoid (resemble like nucleus, but not true nucleus) which contain their vital biomolecules (nuclear protein and DNA). Neither the nuclear apparatus nor the respiratory enzyme systems are separately enclosed by membrane. However, the inner surface of the plasma membrane itself may serve for enzyme attachment. The cytoplasm of such kind of cells lack in well-defined cytoplasmic organelles (endoplasmic reticulum, mitochondria, centrioles, golgi bodies etc). UTTARAKHAND OPEN UNIVERSITY Page 9 CELL BIOLOGY OF PLANTS MSCBOT-506 Reproduction takes place by the vegetative means. Binary fission and budding are the common methods of reproduction in prokaryotes. Sexual reproduction is usually absent; however, if present it is unidirectional transfer of genes from donor to recipient. The mode of nutrition is principally absorption type. However, some blue green algae synthesize their own food due to the presence of photosynthetic pigments. Some examples of the typical prokaryotic cells and cell organization are given below. (i) Pleuropneumonia like organisms (PPLO) The Pleuropneumonia like organisms (PPLOs) are the simplest known cells devoid of cell wall. They are small in size and having deformable triple layer plasma membrane around the cell. PPLO resemble with the bacteria cell which differ with only in the absence of cell wall and mesosomes. Therefore, they are excluded from the group of bacteria. The diameters of the smallest PPLO are 0.1-0.3 µm, and of the largest on the order of a micron. Thus, in size, the PPLOs overleaped with the largest viruses and with the smallest bacteria (Verma and Agarwal, 2008). Mycoplasma is the widely studies genus of the PPLO. Fig. 1.1: Diagram of a typical prokaryotic cell (PPLO) The cell of PPLO (Fig. 1.1) is restricted by a thick (75 Aº) plasma membrane. The granulated ground material called cytoplasm contains vacuoles of undefined significance. At the end of the cell, a bud like structure called bleb is present with less known function. The genetic material (DNA=fibrils form or a single circular double helix) is limited in nuclear region and not enclosed by nuclear membrane. The nuclear region is encircled by many ribosomes and other components involved in protein synthesis. PPLOs are free living and do not required host cell for its multiplication. In PPLO the reproduction takes place by the method of budding, binary fission, formation of tiny spore like bodies and growth of large branched filament that fragmented ultimately and produced as new organisms. UTTARAKHAND OPEN UNIVERSITY Page 10 CELL BIOLOGY OF PLANTS MSCBOT-506 (ii) Bacteria cell Cell organization of a typical bacterial cell (Fig.1.2) is given as below: 1. Outer covering: The outer covering of the bacterial cell possess three layers i.e.: Layer 1: Capsule: It is the outermost, additional protective layer of the bacterial cell which is slimy in nature and made up of polysaccharides. It may or may not be present around the cell wall. Layer 2: Cell wall: After the capsule, a rigid and strong layer is present which is known as cell wall. The cell wall besides containing protein, lipids, carbohydrates, phosphorus and certain inorganic salts, also contains an amino acid diaminopimelic acid (only in bacteria and blue green algae) and a derivative of glucose known as muramic acid. The bacterial cell walls are made of peptidoglycan which is made up of polysaccharide chains cross-linked by unusual peptides containing D-amino acids (van Heijenoort 2001; Koch 2003). Therefore, the cell wall of bacteria is different from the plant and fungi. In plant and fungi, cell walls are made up of cellulose and chitin, respectively. The bacterial cell wall can be divided into two categories i.e., Gram positive and Gram negative according to differences in their cell wall. Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan, teichoic acids and a traces of RNA. In contrast, Gram- negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins. They do not contain teichoic acids and RNA. Layer 3: Plasma membrane: After cell wall, a thin bilayer surrounds the whole cytoplasm. This thin layer membrane is called plasma membrane or cytoplasmic membrane. This layer functioned as a selective permeability barrier that regulates the passage of substances into and out of the cell. The bacterial membrane allows passage of water and uncharged molecules up to molecular weight of about 100 Daltons, but does not allow passage of larger molecules. This membrane also contains the oxidative or respiratory enzymes which have the similar functions as mitochondria in eukaryotic cells. The plasma membrane is composed of a phospholipid bilayer. Bacterial membranes are composed of 40% phospholipid and 60% protein. The phospholipids are amphiphilic molecules with a polar hydrophilic glycerol "head" attached via an ester bond to two nonpolar hydrophobic fatty acid tails, which naturally form a bilayer in aqueous environment. 2. Cytoplasm: The bacterial cytoplasm is a viscous, dense, colloidal and granulated material. All the cell organelles, which are usually present in the eukaryotic organisms, are absent in it. However, no membrane bound, organelles occur in cytoplasm. The ribosomes function in the protein synthesis. UTTARAKHAND OPEN UNIVERSITY Page 11 CELL BIOLOGY OF PLANTS MSCBOT-506 DNA molecule or bacterial chromosome is considered as the genetic material which is confined in a particular region called nucleoid. Certain bacteria are able of photosynthesis with the help of a pigment called bacteriochlorophyll. This photosynthesis pigment and some other enzymes are associated with the internal membranes that are arranged as lamellae, tubules or vesicles in different species. Many bacteria are able to swim freely with the help of thread like structure called flagella, which usually help the bacteria in locomotion. Generally, rod and spiral shaped bacteria regularly contain flagella while it is entirely absent in spherical bacteria. Some bacteria also possess a hair like out growth called pili or fimbriae. Pili somewhat resemble with the flagella including a basal body anchor within the cytoplasm. In most bacteria pili are responsible for recognizing and attaching to the host. In some bacteria, sex pili in male strain play a role to make a bridge with the female cell during mating. Fig. 1.2: A typical bacterial cell 1.3.2 Eukaryotic cells Eukaryotes represent a tiny minority of all living things (Whitman et al. 1998). However, due to their much larger size, their collective worldwide biomass is estimated to be about equal to that of prokaryotes (Whitman et al. 1998). Eukaryotes evolved approximately 1.6–2.1 billion years ago, during the Proterozoic eon. These are the advanced type of cells which may be derived or evaluated from the prokaryotic cells. There is a hudge differences between pro and eukaryotic cells as given below: UTTARAKHAND OPEN UNIVERSITY Page 12 CELL BIOLOGY OF PLANTS MSCBOT-506 Properties Prokaryote Eukaryote Size Generally small < 2 µm in Usually larger. 2 to 100µm diameter in diameter Basics Origin Most primitive Relative new, or evolved from the prokaryote Phylogenetic group Bacteria, Archaea Algae, fungi, protozoa, plnt and animal cell Forms of motility Flagellar Flagella composed of single type Flagella or cillia; composed movement of protein arrange in a fiber; of microtubues; do not flagella rotate rotate Nonflagellar Gliding motility; gas vesicle Cytoplasmic streamlining movement mediated and ameboid movement; gliding motility Nuclear Absent Present membrane Nuclear structure and function Nucleolus Absent Present DNA Single molecule generally Linear, present in several covalently closed and circular, not chromosomes, usually complexed with histones complexed with histones. Division No mitosis Mitosis, mitotic apparatus with microtubular spindle Sexual Fragmentary process, Regular process, meiosis reproduction unidirectional, no meiosis, usually reassortment whole only portions of genetic chromosome complement complement reassorted Introns in genes Rare Common Cytoplasmic Usually lacks sterols: hopanoids Sterols usually present; Cytoplasmic structure and membrane may be present hopanoids absent Internal membrane Relative simple, limited to specific Complex, endoplasmic organization group reticulum and Golgi complex Ribosomes 70S in size 80S, excepts for ribosome of mitochondria and chloroplasts, which are 70S Membranous Absent Several present organelles UTTARAKHAND OPEN UNIVERSITY Page 13 CELL BIOLOGY OF PLANTS MSCBOT-506 Photosynthetic In internal membranes of In chloroplasts pigments chromosomes, chloroplast are absent Respiratory system Part of cytoplasmic membrane In mitochondria Cell wall Present (in most), composed f Present in plant, algae, peptidoglycan (bacteria), other fungi, usually polysaccharides, protein, polysaccharid, absent in glycoprotein animals and most protozoa Endospores Present (in some), very heat Absent resistant Gas vesicles Present (in some) Absent The eukaryotic (Gr., eu- well or true, Karyotic-nucleus) cells are those cells which contain a well-constructed nucleus (nucleus enclosed within the membrane) and membrane bounded cell organelles (Fig. 1.3). Organisms that possess such kind of cells are known as eukaryotes. They are mostly multicellular in organization (Nelson and Cox 2005) which include organisms consisting of many cell types forming different kinds of tissue. For example, animal and plant cells. Difference between animal and plant cells: 1. Shape and Size: Plant cells are 10-100 micrometers in length, typically rectangular or cubic in shape, however animal cells are 10-30 micrometers in length and irregular in shape. 2. Energy store: Animals cells store energy in the form of the complex carbohydrate glycogen. Plant cells store energy as starch. 3. Differentiation: In animal cells, only stem cells are capable of converting to other cell types. Most plant cell types are capable of differentiation. 4. Growth: Animal cells increase in size by increasing in cell numbers. Plant cells mainly increase cell size by becoming larger by absorbing more water into the central vacuole. 5. Cell Wall: Animal cells do not have a cell wall but have a cell membrane. Plant cells have a cell wall composed of cellulose as well as a cell membrane. 6. Centrioles: Animal cells contain these cylindrical structures that organize the assembly of microtubules during cell division. Plant cells do not typically contain centrioles. 7. Lysosomes: Animal cells possess lysosomes which contain enzymes that digest cellular macromolecules. In plant cells vacuole handles molecule degradation. UTTARAKHAND OPEN UNIVERSITY Page 14 CELL BIOLOGY OF PLANTS MSCBOT-506 8. Plastids: Animal cells do not have plastids. Plant cells contain plastids such as chloroplasts, which are needed for photosynthesis. 9. Plasmodesmata: Animal cells do not have plasmodesmata. Plant cells have plasmodesmata, which are pores between two plant cell walls that allow molecules and communication signals to pass between individual plant cells. 10. Vacuole: Animal cells may have many small vacuoles. Plant cells have a large central vacuole that can occupy up to 90% of the cell's volume. Fig. 1.3: Typical eukaryotic cells (animal and plant cell) Eukaryotes possess the true nuclear, which contains chromatin fibres, nucleoplasm, nucleolus etc. remain separated from the cytoplasm by the thin perforated nuclear membranes. Apart from the true nucleus, eukaryotic cells also possess some other membrane-bound organelles such as endoplasmic reticulum, golgi apparatus, mitochondria etc. In addition, group of photosynthesis plants also contain chloroplasts. The process of reproduction takes place by both asexual and sexual methods in eukaryotes. They can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. Before UTTARAKHAND OPEN UNIVERSITY Page 15 CELL BIOLOGY OF PLANTS MSCBOT-506 going to the detail of the eukaryotic cells, it is advisable to known the general characteristics of different types of eukaryotic cells. 1.3.2.1 Shape The eukaryotic cells exhibited various forms and shapes (Fig. 1.4). The shape may vary with animal to animal or organ to organ. Even the cells of the same organ may display variations in the shapes. The shape of the cells may depend upon the following; (i) Functional adaptations of the cell. (ii) Internal or external environment of the cell. (iii) Mechanical stress or pressure and surface tension of the cell. (iv) Viscosity of the protoplasm. (v) Mechanical action exerted by the adjoining cell. (vi) Rigidity of the cell membrane. Typically the animal cell is spherical in shape but irregular, cylindrical, cuboidal, triangular, tubular, polygonal, oval, round elongated etc have also been seen in different organisms. Some cells (Amaeba and leucocytes) able to change their body shape very frequently. 1.3.2.2 Size Generally, the eukaryotic cells are microscopic in nature but some animals and plant cells are easily visible by the necked eyes. For example: the egg of ostrich is the largest cell in the diameter, some nerve cells are considered more than 3-5 feet in length (Verma and Agrawal 2008). Usually, the size of cells may vary between 1µm and 175000 µm (175 mm). 1.3.2.3 Number The body of the unicellular and acellular organisms (protozoa and protophyta) is composed by a single cell. Most of the eukaryotic cells have many cells in the body therefore known as multicellular organisms. The numbers of the cells in particular organisms depend upon the size of the organisms. Usually, larger in size have the great number of the cells in their body. The number of cells in eukaryotic organisms varies from single cell to trillions. For example in the unicellular organisms a single cell is present however, the human body contain approximately 26 trillions cells, 5 million erythrocytes cells per cubic ml in blood and 10 billion neurons in nervous system. UTTARAKHAND OPEN UNIVERSITY Page 16 CELL BIOLOGY OF PLANTS MSCBOT-506 Fig. 1.4: Various types of eukaryotic cells exhibiting diverse shapes; (A). human sperm, (B). leucocyte, (C). diatom, (D). goblet cell, (E). ceratium, (F). epithelial cell, (G). Ostrich egg, (H). choanocyte, (I). osteocyte, (J). chromatophore, (K). muscle cell, (L). nerve cell 1.3.2.4 Structure The eukaryotic cells are well defined cell. It can be categorized in the following components: (A) Cell wall and plasma membrane, (B) Cytoplasm and (C) Nucleus (A) Cell wall and plasma membrane: Cell wall is the characteristic feature of the plant cells which is completely absent in animal cells. The protoplasm of the plant cells become separated from the external environment by a laminated, semi rigid and the layer of non-living cells known as cell wall. The composition of the cell wall depends upon the species, type of cell, function and developmental process. Usually, the plant cell wall is composed of the polysaccharide cellulose, hemicellulose and pectin. Some polymers (lignin, suberin and cutin) are also embedded in plant cell wall. Glycoproteins and polysaccharides such as carrageenan and agar exclusively occur in the cell wall of few algae which are completely lacking in land plants. The UTTARAKHAND OPEN UNIVERSITY Page 17 CELL BIOLOGY OF PLANTS MSCBOT-506 cell wall of diatoms is composed of biogenic silica. The composition of fungal cell wall is quite different from the plant which is made up of N-acetylglucosamine polymer chitin. The main functions of cell wall are to provide the shape, support, strength, rigidity, and protection against mechanical/ biological stress. The cell wall of certain plants possesses the pit like small apparatus known as plasmodesmata which help to connect the cell to the adjacent cell. Most plant and animal cells have an external covering of living, thin, porous and semipermeable cells known as plasma membrane or cell membrane. This membrane is composed of three layers in which the inner and outer layers are constituted by protein and middle layer by lipid. Technically, plasma membrane gives the mechanical strength to the cell. It is selectively permeable to ions and organic molecules thus regulate the movement of substances in the cells. (B) Cytoplasm: The plasma membrane is followed by a cytoplasm which can be divided into two parts i.e., (1) cytoplasmic matrix and (2) cytoplasmic structures. (1) Cytoplasmic matrix: The space between the plasma membrane and the nucleus is occupied by the gel like, translucent and homogenous colloidal liquid known as cytoplasmic matrix or hyaloplasm. The 90 % of the cytoplasm is constituted by water. Remaining 10% is constituted by various inorganic compounds including salts of Na, K and minerals, organic compounds such as carbohydrates, lipids, fats, proteins, vitamins, nucleoproteins, nucleic acids (RNA and DNA) and enzymes. The peripheral region of cytoplasmic matrix is comparatively non granular, viscous, clear and rigid as known as the plasmagel, cortex or cortical layer and ectoplasm. On the other hand the inner region is granular, less viscous and known as endoplasm. The main function of the cytoplasmic matrix is to conduct the various vital activities of the cells. Some important functions are listed as:  Biosynthesis of biochemical substances (proteins, carbohydrates, proteins, nucleic acid etc).  The process of glycolysis, anaerobic respiration and pentose pathway type of respiration occur in the matrix part of cytoplasm.  The cell organelles are usually unconnected. They exchange materials through the cytoplasmic matrix.  The products of cell organelles are passed out into the matrix.  The cytoplasmic matrix is always in motion. It is autonomic and is called cytoplasmic or protoplasmic streaming. This helps in distribution of various materials inside the cell. (2) Cytoplasmic structures: In the cytoplasmic matrix, some non-living and living substances are suspended. The non-living substance grouped under paraplasm, deutoplasm or cytoplasmic inclusions while the living, membrane bounded structure are called organoids or organelles (Fig. 1.5). (i) Cytoplasmic inclusions: The stored food and secretory substances of the cell remain suspended in the cytoplasmic matrix in the form of granules which form the cytoplasmic UTTARAKHAND OPEN UNIVERSITY Page 18 CELL BIOLOGY OF PLANTS MSCBOT-506 inclusions. It includes oil drops, yolk granules, pigments, secretory granules, starch granules in plant whereas glycogen granules in animal cells. (ii) Cytoplasmic organelles: The organelles are the living structure of the cytoplasm having double membrane. They perform various important biosynthesis and metabolic activities such as respiration, transportation, support, storage and reproduction. Some most important cell organelles are discussed below: a. Microtubules: The cytoplasm of eukaryotic cells is traversed by many ultrafine tubes of tubulin protein called microtubules (Fig. 1.5A). It is complex structure generally comprised of thirteen individual protofilaments arranged to form a hollow cylinder. Microtubules are filamentous intracellular structures that are responsible for various kinds of movements including transportation of water, ions or small molecules, cytoplasmic streaming in all eukaryotic cells. Microtubules are also involved in asters formation in the mitotic and meiotic spindle during cell division. Moreover, they form the structural units of the centrioles, basal granules, cilia and flagella. b. Cytoplasmic filaments: The cytoplasm is fastened with ultrafine, tube like, proteinous and soil filaments of various sizes. There are three types of cytoplasm filaments. The smallest is microfilaments around 40 to 60 A° in diameter that occur next to plasma membrane where they form the web in ectoplasm. The second class is myosin filament. It is also called actin filaments. Microfilaments are usually about 7 nm in diameter and made up of two strands of actin. This filament is involved in many kinds of cell movements including division, various extension of the cell surface, such as microvilli. In addition of both the above mentioned filaments, a third class of filament simply called 100 A° filaments. These filaments are involved in movement in both the cell itself and of material within the cell. c. Centrosome: The centrosome possesses thick cytoplasm and located adjacent to nucleus. This cell organelle is found only in the animal cells, not in the plant and fungal cells (Fig. 1.5 B). The centrosome is composed of two centrioles at right angles to each another. They are surrounded by a shapeless mass of protein. A centrosome is the site where microtubules are organized. Other than this, it plays an important role in cell division in animal cell especially where one cell divining into two daughter cells. UTTARAKHAND OPEN UNIVERSITY Page 19 CELL BIOLOGY OF PLANTS MSCBOT-506 Fig. 1.5: Various types of eukaryotic cell organelles; (A). Microtubues, (B). Centrosome, (C). Cilia, (D). Flagella, (E). Endoplamic reticulum, (F). Ribosome, (G). Golgi bodies, (H). Lysosomes, (I). Mitochondria, (J). Chloroplast, (K). Nucleus UTTARAKHAND OPEN UNIVERSITY Page 20 CELL BIOLOGY OF PLANTS MSCBOT-506 d. Cilia and flagella: The cells of the many unicellular organisms and ciliated epithelium of multicellular organisms consist of some hair like cytoplasmic outgrowth on the surface of the cell. These are known as cilia or flagella. There is some difference between cilia and flagella. Cilia are typically 2-10 µm long and 0.5 µm in diameter, however, flagella are longer (100-200 µm) in size (Fig. 1.5 C & D). Usually there are no more than one or two flagella in a single cell. Both cilia and flagella help in the locomotion. e. Endoplasmic reticulum: In a eukaryotic cell, endoplasmic reticulum (ER) is a reticulated organelle of the cytoplasm. They form an interconnected network of flattened, tubular structures known as cisternae (Fig. 1.5 E). Usually, endoplasmic reticulum present in all the eukaryotic cells, however, some cells (spermatozoa and red blood cells) do not contain it. ER continues to the outer membrane of the nucleus. Endoplasmic reticulum can categorize into two types according to variation in its structure; (i) Rough Endoplasmic Reticulum (RER) (ii) Smooth Endoplasmic Reticulum (SER). The ribosomes remain attached to the outer surface of RER which gives a rough appearance; therefore, it is called rough endoplasmic reticulum. It frequently occurs in cells such as hepatocytes and site of protein synthesis. On the other hand, the smooth endoplasmic reticulum lacks ribosomes and functions in lipid synthesis but not metabolism, the production of steroid hormones and detoxification. The smooth ER is especially abundant in mammalian liver and gonad cells. Other than the above mentioned functions, endoplasmic reticulum forms the ultrastructure skeleton framework of the cytoplasmic network and provides mechanical support. f. Golgi complex: The Golgi complex or Golgi body, or Golgi apparatus, or Golgi is a cytoplasmic organelle found in most eukaryotes (Fig. 1.5 G). It was discovered by Camillo Golgi in 1897. Golgi complex is made up of a series of compartments and is a collection of fused, flattened membrane-enclosed disks known as cisternae, originating from vesicular clusters that bud off the endoplasmic reticulum. Each Golgi is composed of many lamellae, tubules, vesicles and vacuoles. The functions of Golgi complex are storage of proteins and enzymes secreted by ribosomes and transported by endoplasmic reticulum. In plants cells the Golgi complex is known as dictyosome that secretes necessary materials for cell wall formation during cell division. It is of particular function of storage of proteins and enzymes which are secreted by ribosomes and transported by endoplasmic reticulum. Further, it has most important secretory function is secreting many secretory granules and lysosomes. The Golgi apparatus tends to be larger and more numerous in cells that synthesize and secrete large amounts of substances for example, the antibody- secreting plasma B cells of the immune system have prominent Golgi complexes. g. Lysosomes: The cytoplasm of animal cell possessing numerous membrane- bound organelles originated from the Golgi complex is called lysosomes (Fig. 1.5 H). They are spherical or irregular vesicles that contain hydrolytic enzymes which help to break UTTARAKHAND OPEN UNIVERSITY Page 21 CELL BIOLOGY OF PLANTS MSCBOT-506 down the biomolecules (carbohydrates, lipids, proteins). They are not only accountable for breaking down of biomolecules but also help to get rid of waste products of the cell. A lysosome has a specific composition, of both its membrane proteins, and its lumenal proteins. Besides degradation of biomolecules, they are involved in secretion, plasma membrane repair, cell signaling, and energy metabolism. It is commonly called ―suicide bags of cell‖. Lysosomes are known to contain more than 60 different enzymes, and have more than 50 membrane proteins. Enzymes of the lysosomes are synthesised in the rough endoplasmic reticulum. The lysosomes of plant cells are storage granules containing hydrolytic enzymes and are comprised of spherosomes, aleurone grain and vacuoles. h. Cytoplasmic vacuoles: The vacuole is a membrane-bound, closed sacs of membranes filled with organic or inorganic molecules. They do not have a certain size and shape, wither cell can change them. The entire vacuole contains a watery substance called cell sap. They are much more important in plant and fungus cells than in animal cells. Some common functions of a vacuole are to grasp waste products, maintain amount of water in plant cells, balance internal hydrostatic pressure or turgor steady in a cell, maintain pH inside of the cell and hold small molecules. Vacuoles are also important in autophagy. In protists, vacuoles also store and help digested food. The vacuoles of the plant cells are bounded by a single, semipermeable membrane known as tonoplast. These vacuoles contain water, phenol, flavonols, anthocyanins, alkaloids, and stored product such as sugar and proteins. i. Microbodies: The cytoplasmic matrix of many kind of cells (yeast, protozoa, cells of higher plants etc) contains certain roughly spherical, membrane bounded particles (0.3-1.5 µm diameter). These particles have a central granular or crystalloid core containing some enzymes; occur in intimate relation with endoplasmic reticulum, mitochondria and chloroplast are called microbodies. It contains enzymes that participate in the preparatory or intermediate stages of biochemical reactions within the cell. This facilitates the breakdown of fats, alcohols and amino acids. Generally, microbodies are involved in detoxification of peroxides and in photorespiration in plants. j. Ribosomes: The ribosomes are the small, spherical structured, minute organelle of cytoplasm (Fig. 1.5 F). It is found in all the living organisms (including prokaryotes and eukaryotes). The ribosomes are originated in the nucleolus and consist of mainly the ribonucleic acids (RNA) and proteins. In eukaryotic cells they are attached with the membrane of endoplasmic reticulum, or occur freely in the cytoplasm. The eukaryotic ribosomes are differ structurally from the prokaryotic ribosomes, however, in both kind of cells, it is the site of protein synthesis. In prokaryotic cell, the ribosomes (70S type) consist of with two ribosomal subunits: the small subunits (30S) and large subunits (50S). On the other hand, the eukaryotic ribosomal subunits (80S type) are composed of 40S as small UTTARAKHAND OPEN UNIVERSITY Page 22 CELL BIOLOGY OF PLANTS MSCBOT-506 subunit and 60S as large subunit. In ribosomes, the small ribosomal subunits read the mRNA, and the large subunits join amino acids to form a polypeptide chain. Each subunit consists of one or more ribosomal RNA (rRNA) molecules and a variety of ribosomal proteins (Weiler and Nover 2008). k. Mitochondria: The shape, size and number of mitochondria varied from cell to cell. Generally, they are rod and round shaped having double membrane bound structure, occurring in most eukaryotic cells, however, some cells lack of them (for example, mature mammalian red blood cells). Both the inner and outer layer along with the central region are filled with a viscos fluid known as mitochondrial matrix. The outer membrane forms a bag like structure around the inner membrane which gives out many fingers like folds in the lumen of the mitochondria. The folds of the inner membrane are known as cristae (Fig. 1.5 I). The matrix, outer and inner membranes possess many oxidative enzymes and coenzymes. The main functions of mitochondria are respiration, oxidation of food and metabolized the energy. They store the energy and release when needed in the various vital activities of life. Mitochondria generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy (Campbell et al. 2006); therefore, named the ―power house of the cell‖. l. Plastids: Plastids are known as the ―kitchen of the cell‖. The plastids exhibit only in plant cells and completely absent in animal cells. They give the particular colour to the plants. The size of plastids range from 4 to 6 µm and colour from colorless to many colours. The colourless plastids are known as leucoplast. They functions specially for the storage of starch, lipids and proteins, therefore, they are called amyloplasts, lipoplasts and proteinoplasts, respectively. The coloured or pigmented plastids commonly called as chromoplast occur in many colours, in which the green is the most common. The green coloured plastid is known as chloroplast (Fig. 1.5 J) which helps in the biosynthesis of food by the process of photosynthesis. The chloroplasts have complicated organization and contain DNA, ribosomes and complete protein synthesis machinery. (C) Nucleus: The nucleus is well defined, centrally located and spherical cellular component which regulate all the vigorous process of the cell. Nucleus is constituted by the three structures (Fig. 1.5 K). a. Nuclear membrane: Nuclear membrane is the outer most layer of the nucleus and occurs in both plant and animal cells. The nuclear membrane is made of two layer of lipoprotein. It forms an envelope like structure around the nucleus known as nuclear envelop. The nuclear envelop contain many tiny pore which regulate the movement of the chemical substance. The outer nuclear membrane of nuclear remains continues with the membrane of endoplasmic reticulum and plasma membrane. The main function of the nuclear membrane is to create a barrier that physically protects the genetical material of the cell from the chemical reactions that are occurring elsewhere in the cell. UTTARAKHAND OPEN UNIVERSITY Page 23 CELL BIOLOGY OF PLANTS MSCBOT-506 b. Nucleoplasm and chromosomes: Like the cytoplasm, the nucleus contains a watery substance called nucleoplasm or karyoplasm. The space between the nuclear membrane and nucleolus is filled by nucleoplasm. It contains dissolved phosphorus, ribos sugar, proteins, nucleotides and nucleic acids. The nucleoplasm contains some threads like structure called the chromosomes. The chromosomes appear only during the cell division otherwise they occur in the form of chromatin granules. The chromosomes and chromatin granules contain the genetic materials along with the many nucleoproteins. c. Nucleolus: The nucleoplasm contains a conspicuous darkly stained spherical body known as the nucleolus. Chemically, nucleolus is composed of large amount of ribosomal protein and ribosomal RNA. The nucleolus stores the rRNA molecules synthesized by nucleolar organizer region of DNA and provides the raw material such as different kind of rRNA's and ribosomal proteins for the biogenesis of ribosomes. 1.4 SPECIALIZED PLANT CELL TYPES The multicellular organism are composed of different type of cells which are designed to perform the specific activates. The cells are distinguished from each other by their shape, size, properties of the cell wall and protoplast. The similar type of cells performed the similar type of work and organized into tissues, which ultimately forms the organs. A tissue system may be constitute by many specialized cells to perform a particular function or may carries out different functions or few cells are found in more than one tissue systems. Many specialized cells are present in plants (Fig.1.6) which makes them unique from others. For example, in plants, cell wall is the prominent distinguishing features of the different kinds of specialized cells. The primary cell wall of plants is made up of cellulose and carbohydrates. Furthermore, a thick, rigid secondary cell wall is also present which is made up of cellulose impregnated with lignin. Other than the cell wall many other specialized cells are also present in the plants. Therefore, for the suitability, the specialized cell types in plant (roots stems, leaves, stem appendages and fruits) can be categorized into three different tissue systems; 1. Ground tissue system: Provides support, photosynthesis and storage. 2. Dermal tissue system: Provides protection and gaseous exchange. 3. Vascular tissue system: Transports water and solutes over long distances within the plant. 1.4.1 Cells of the ground tissue system The ground tissue system is originated by the ground meristems and function to synthesize the organic compounds that support, and protect the plants. In some cases, the ground tissue also stores UTTARAKHAND OPEN UNIVERSITY Page 24 CELL BIOLOGY OF PLANTS MSCBOT-506 food in the form of starch. Basically, the ground tissue system is made up of three types of cells; parenchyma, collenchyma and sclerenchyma. a. Parenchyma cells: These are the living, generalized, multipurpose, thin walled cells and range from spherical to barrel-like in shape. The parenchymatic cells of leaves are adapted for photosynthesis due to the presence of many chloroplasts, therefore, they are called chlorenchyma cells. In some species, parenchyma cells often store food reserves. For example, in potato and apple the cells store starch and sugar, respectively. Sometime, these cells are specialized for transportation of solute across the membrane and called as the transfer cells. Transfer cells are common in nectaries. b. Collenchyma cells: These are the living, elongated and irregularly thickened primary cell walls composed of cellulose. The secretory apparatus (ER and Golgi) proliferates to secrete additional primary wall. Collenchyma cells develope from meristem cells that initially resemble parenchyma, but differentiate quickly becoming apparent. Plastids do not develop in it, therefore, these cell do not help in the photosynthesis. The main functions of these cells are in the support of growing tissues especially the stem and leaves. Collenchyma cells form long cables of thousands of cells that together can provide mechanical support during stem and leaves elongation. Collenchyma is common in the veins of leaves and forms the strings of celery stalks. c. Sclerenchyma cells: The sclerenchyma cells are dead, elongated, rigid, heavily thickened secondary walls containing lignified cells. These cells frequently occur in those meristematically inactive regions (bark or old trunk) of the plant. Unlike both parenchyma and collenchyma cells, sclerenchyma cells become dead at maturity. These cells provide mechanical support to tissues that are no longer expanding. Sclerenchyma fibers make up the bulk of woody tissues and also form long strands in the leaves and stems of many plants. Natural fiber ropes (hemp or sisal plants) are made up of sclerenchyma fibers. Some sclerenchyma cells called sclereids are much shorter than the fibers; these form the hard layers of walnut shells and peach pits, and small clusters of sclereids form the grit in pear fruits. 1.4.2 Cells of the dermal system The dermal tissue system protects the soft tissues of plants and controls interactions with the plants to the surroundings. The examples of specialized plant cell of dermal system are given below; a. Epidermal cells: These cells comprise of numerous types of cells which constitute the outer covering of plants called epidermis layer. Usually the cells of epidermis are flat and form a continuous sheet with no spaces between the cells. Most epidermal cells also secrete waxes on the surface of the cutin, which further reduces transpiration, as well as wettability of the leaf surface. The cells of epidermis vary in shape and size. They may be irregular UTTARAKHAND OPEN UNIVERSITY Page 25 CELL BIOLOGY OF PLANTS MSCBOT-506 wavy shape (in Arabidopsis thaliana), interlocking jigsaw puzzle pieces like (in the leaves of many dicots), and rectangular (in stem and elongated plant organs). Therefore, the shape of the epidermis depends upon the functions and organs where they are located. Epidermis layer serves numerous important functions in plant. The main function is to provide the protection to the plant cell from a variety of external harmful factors (environmental stressors) including microbes, chemical compounds as well as physical influences. Apart from the protection, these layers prevent the loss of water from the exposed area of plants. b. Guard cells: These are the specialized epidermal cells that function to open small pores in the plant surface, allowing the CO2 needed for photosynthesis to diffuse from the external atmosphere into the chlorenchyma tissue. Guard cells are usually crescent-shaped, contain green chloroplasts, and are able to rapidly change their shape in response to changes in water status. As guard cells take up water, the pore opens as they lose water the pore closes. The two guard cells and pore are termed a stomate. They surround each stoma and help to regulate the rate of transpiration by opening and closing the stomata. c. Trichomes: The word trichome is derived from a Greek word meaning hair. These are like a fine outgrowths or appendages on plants, algae, lichens, and certain protists which project from the surface of the body of the organisms. They may vary in shape and size according to the species. They are reported as simple, straight, spiral, hooked, glandular, peltate and etellate in various organisms. In plants, they function to reduce the water loss through the trapping of water vapor near the plant surface. In some plants trichomes serve protection by secreting sticky or toxic substances that repel insect herbivores. 1.4.3 Cells of the vascular system The vascular system of the plant is composed of xylem and phloem cells. Both the components regulate the supply of food and water in the plant. a. Xylem cell: Xylem is made up of several types of cells i.e., xylem tracheids, xylem vessel and xylem parenchyma. Xylem tracheids are the long elongated cells that help transport xylem sap and also provide structural support. Vessels are shorter than tracheids, but also help to conduct water. They are generally found in angiosperm plants (flowering plants) but not in gymnosperms. Vessel elements have perforation plates that connect each vessel element to form one continuous vessel. Xylem also contains parenchyma, a tissue that makes up most of the soft parts of plants, and long fibers that help support the plant. b. Phloem: Phloem tissue functions to transport the prepared food after process of photosynthesis to the various part of the plant where energy-rich carbohydrates are required for storage or growth. Sieve elements are the conducting cells of the phloem which are elongated and thick primary wall. Sieve elements have large, conspicuous pores on the end UTTARAKHAND OPEN UNIVERSITY Page 26 CELL BIOLOGY OF PLANTS MSCBOT-506 walls, forming a sieve plate. The sieve plate pores allow the phloem sap to travel from cell to cell along the file of cells called a sieve tube. Each sieve element is living with an intact plasma membrane; the differential permeability of the membrane prevents solutes from leaking out of the sieve tube. Sieve-tube elements lack a nucleus and some other components of the cytoplasm; this feature functions to keep the pores unplugged. Companion cells are small parenchyma cells associated with each sieve element. The nucleus of the companion cell must direct the metabolism of both the companion cell itself and of its sister sieve element. Fig. 1.6: Some specialized plant cell types 1.5 CHEMICAL COMPOSITION The chemical composition of a cell can be categorized into two parts: inorganic compounds and organic compounds. UTTARAKHAND OPEN UNIVERSITY Page 27 CELL BIOLOGY OF PLANTS MSCBOT-506 1.5.1 Inorganic compounds The inorganic compounds normally occur in physical, non living universe such as elements, metals, non metals and their compounds like water, salts and the verities of the electrolytes and non electrolytes. From the 104 elements of the universe, the cytoplasmic matrix contains only 36 elements (Verma and Agrawal, 2008). Generally they are grouped into three categories: Occur predominantly in matrix, e.g., oxygen, carbon, hydrogen and Major constituent : nitrogen. Occur in low percentage in matrix, e.g., calcium, phosphorus, Trace element : chlorine, sulphur, potassium, sodium, magnesium, iodine and iron. Ultrastructure Occur in the matrix in 0.756%. The remaining 23 elements are : element copper, cobalt, manganese, zinc, molybdenum, boron, silicon etc. These inorganic compounds play the vital role in the various biological and chemical activities in the cell. Various physiological activities such as osmosis, diffusion, impulse conduction etc are influenced by the trace inorganic compounds. Ultrastructure elements play an important role as cofactors in various chemical reactions. Water: It is the most abundant inorganic compound of the cell and constitute about 70-80% of the matrix. They occur in the two forms viz., free water and bound water. About 95% water of the matrix is free water and functions as the solvent for many substances. The remaining 5% of the cellular water remains loosely linked with protein molecules by hydrogen bonds and known as bound water. Functions of water 1. Water is the best solvent for the various cellular substances. 2. It is the main component of the process of photosynthesis in the plant. Without it, plant cannot synthesize their food. 3. Water forms the good dispersion medium for the colloidal systems of the matrix. 4. Water serves as a natural stabilizer for the atmospheric temperature. 5. It has greater importance for the various metabolic functions because most of them require the exclusively aqueous medium. 6. Water is used by the cell as a transporting media for the food, nitrogen waste and other necessary substances. 1.5.2 Organic compounds The chemical substances which contain the carbon in combination with one or more other elements as hydrogen, nitrogen, sulphur etc are called organic compound. Usually they are the large molecules formed by the similar or dissimilar unit structure known as the monomers. UTTARAKHAND OPEN UNIVERSITY Page 28 CELL BIOLOGY OF PLANTS MSCBOT-506 The four main classes of molecules (viz., carbohydrates, lipids, proteins and nucleic acids) occurring in the cells are called biomolecules (Slabaugh and Seager, 2013) in a typical cell. Many small micromolecules get linked together to prepare a large macromolecule known as polymers and this process is known as dehydration synthesis. The detail description of chemical composition (organic) of the cell is given below: 1.5.2.1 Carbohydrates Carbohydrates are the main source of the energy in all living organisms on the Earth. Only green plants and few groups of microbes are able to synthesize the carbohydrate from the water and carbon dioxide in the presence of the Sun light and chlorophyll pigment. Therefore, all the animals, non-green plants (fungi) and bacteria depend on green plants for the supply of the carbohydrates. Carbohydrates can be represented by the stoichiometric formula (CH2O)n, where n is the number (at least 3) or CnH2nOn. The ratio of carbon to hydrogen to oxygen represents as 1:2:1 in carbohydrate molecules. They are called carbohydrate because as the formula explains itself that it is buildup of the components of carbon (carbo) and water (hydrate). Carbohydrates are classified into three subtypes: monosaccharaides, disaccharides, and polysaccharides. (a) Monosaccharides: Monosaccharides (mono= one, sacchar= sweet) are the simplest type of the carbohydrate. Here the number of carbon is restricted three to seven in number and their names end with the suffix ―-ose”. Depending upon the numbers of carbon molecules they may be known as trioses (C=3, e.g., glyceraldehydea and dihydroxy acetone), tetrose (C=4 e.g., erythrose), pentoses (C=5, e.g., ribose, deoxyribose, arabinose and xylulose), hexoses (C=6, e.g., glucose, fructose and galactose) and heptose (C=7, e.g., sedoheptulose). If the sugar has an aldehyde group (the functional group with the structure R-CHO), it is known as an aldose, and if it has a ketone group (the functional group with the structure RC(=O)R′), it is known as a ketose (Fig. 1.7). UTTARAKHAND OPEN UNIVERSITY Page 29 CELL BIOLOGY OF PLANTS MSCBOT-506 Fig. 1.7: Showing the Aldoses (R-CHO at the end of the carbon chain) and keto (R-CO at the middle of the carbon chain) group in the monosaccharide. Triose, Pentose and Hexose have three, five and six carbon, respectively Example: Glucose, galactose and fructose are the example of monosaccharide. They all are hexose sugars having similar chemical formula (C6H12O6), therefore, known as isomers. However, chemically and structurally, they are differ from each other because of arrangement of functional groups around the asymmetric carbon (Fig. 1.8). Glucose is one of the most important monosaccharides, fructose, the sugar commonly associated with the sweet taste of fruits, and galactose occurs in the milk. Fig.1.8: Isomers of hexose sugar (Glucose, Galactose and fructose) UTTARAKHAND OPEN UNIVERSITY Page 30 CELL BIOLOGY OF PLANTS MSCBOT-506 (b) Oligosaccharides: The oligosaccharides consist of 2 to 10 monosaccharides in a single molecule of oligosaccharide. The monosaccharides are pooled together by the specific covalent bond called glycosidic bond and a molecule of water is released. In this process, OH group of one monosaccharide joins with the hydrogen group of another molecule of monosaccharide and form a water molecule. Therefore, one molecules of disaccharide is made up of two molecules of monosaccharides. Therefore, when reverse reaction takes place the glycosidic bond of a disaccharide broken into two monosaccharides is termed hydrolysis, for example, the molecules of disaccharides (contain two monomers). The most abundant oligosaccharides of the animal and the plant cells are disaccharides such as sucrose, maltose and lactose. The sucrose (Fig.1.9) and maltose occur mainly in the plant cells, whereas the lactose occurs exclusively in the animal cells. Fig. 1.9: Formation a molecule of sucrose (oligosaccharides) by joining one molecules of glucose and one molecules of fructose Certain important oligosaccharides are: disaccharides (two monomers, e.g., sucrose, maltose, lactose etc), trisaccharides (tree monomers e.g., raffinose, mannotriose, rabinose, rhaminose, gentianose and melezitose), tetrasaccharides (four monomers e.g., stachyose, scordose), pentasaccharides (five monomers e.g., verbascose). (c) Polysaccharide: The polysaccharides are the group of carbohydrate composed of ten to many thousands monomers of monosaccharides in their macromolecules. The macromolecules of this group contain colloidal size with high molecular weights. Polysaccharide can be subdivided into two categories. i.e., homo-polysaccharide (contain similar type of monosccharides in their molecules, e.g., starch, cellulose, glycogen etc), hetro-polysaccharide (contain different type of monosccharides and amino-nitrogen or sulphuric or phosphorus acids in their molecules, e.g., chitin, heparin etc). Functions of Carbohydrate 1. The glucose, a hexose sugar is the main source of energy in all living organisms. Fructose is also an important source of energy. 2. Carbohydrate functions as the main structural elements in plants in two forms i.e., cellulose and hemicellulose. Cellulose, a polysaccharide, is used to build the cell wall. UTTARAKHAND OPEN UNIVERSITY Page 31 CELL BIOLOGY OF PLANTS MSCBOT-506 3. Carbohydrates give the mechanical support to the plant body. 4. The pentose sugar, ribose is the important constitution of the ribonucleic acid (RNA) and certain co enzymes as Nicotinamide Adenine Dinucleotide (NAD), Nicotinamide Adenine Dinucleotide Phosphate (NADP), Adinosine triphosphate (ATP) and coenzyme A (CoA). Another pentose sugar dioxyribose is an important constitute of genetic material, dioxyribonucleic acid (DNA). 5. Polysaccharides such as starch serve as storage molecules. Plants store starch in root, tuber and leafy parts mainly during photosynthesis activity. 1.5.2.2 Lipids (Fats) The lipids (Gr., lipos=fats) are the organic compound which are insoluble in water whereas soluable in organic compound (chloroform, ether, alcohol, benzene and other organic compound) (Fig. 1.10). Lipids are non polar and hydrophobic in nature. The lipids are classified into three classes. (a) Simple lipids: These are the esters of the alcohols or the triglycerides containing fatty acids and alcohols. The composition of this type of class may be saturated, e.g., palmatic acid, stearic acid etc. or unsaturated, e.g., oleic acid, linolenic acid, arachedonic and clupanadonic acid. The simple lipids of the matrix are given: i. Natural fats: These are the naturally occurring fats in animal and plant cells in the form of stored food substances. ii. Wax: These are the esters of fatty acids of high molecular weight with the alcohol except the glycerol. The most important constituent alcohol of the molecules of wax is the cholesterol, bee wax. (b) Compound lipids: The compound lipids contain fatty acids, alcohols and other compounds such as phosphorus, amino-nitrogen carbohydrates etc in its molecules. Steroids, phospholipids, glycolipids, lipoproteins and carotenoids are some of the examples of the compound lipids. (c) Derived lipids: These are the group of lipids which are derived from the simple or compound lipids by hydrolysis. These include fatty acids, alcohols, monoglycerides and diglycerides, steroids, terpenes, and carotenoids. The most common derived lipids are steroids, terpenes and carotenoids. UTTARAKHAND OPEN UNIVERSITY Page 32 CELL BIOLOGY OF PLANTS MSCBOT-506 Fig. 1.10: Structure of some common lipids. At the top are cholesterol and oleic acid. The middlestructure is triglyceride composed of oleoyl, stearoyl and palmitoyl chains attached to a glycerolbackbone. At the bottom is the common phospholipid phasphatidylcholine (Maitland, 1998) Functions of lipids 1. The lipids are important constituents of the cellular membrane, hormones and vitamins of the cells. 2. They serve as the source of energy in the cells. 3. Lipids, especially phospholipids, are also used in various pharmaceutical products either as co-solubilisers (e.g., in parenteral infusions) or else as drug carrier components (e.g., in a liposome or transfersome). 4. Protective wax coating found in certain group of plants. 5. In plants, seed oils such as triacylglycerols (TAGs) provide food storage for seed germination and growth in both angiosperms and gymnosperms. 6. Lipids provide to the plants the necessary energy for their metabolic processes and signals between cells. UTTARAKHAND OPEN UNIVERSITY Page 33 CELL BIOLOGY OF PLANTS MSCBOT-506 1.5.2.3. Proteins Proteins are very large molecules (macro-biopolymers) made up of monomers called amino acids. An amino acid consists of an alpha carbon atom attached to an amino group, –NH2, a carboxylic acid group, –COOH (although these exist as –NH3+ and –COO− under physiologic conditions), a simple hydrogen atom, and a side chain commonly denoted as "–R". The side chain "R" is different for each amino acid of which there are 20 standard ones. It is this ―R‖ group that makes each amino acid different, and the properties of the side-chains greatly influence the overall three-dimensional conformation of a protein. Amino acids can be joined via a peptide bond. In this dehydration synthesis, a water molecule is removed and the peptide bond connects the nitrogen of one amino acid's amino group to the carbon of the other's carboxylic acid group. The resulting molecule is called as dipeptide, and short stretches of amino acids (usually, fewer than thirty) are called peptides or polypeptides. Longer stretches merit the title proteins. The structure of proteins is traditionally described in a hierarchy of four levels. a. Primary structure: Primary structure of a protein consists of its linear sequence of amino acids found in the protein. It is determined by the covalent peptide bonding between amino acids. Primary structure also includes the other covalent bonds in proteins. b. Secondary structure: Secondary structure is concerned with local morphology. It is any regular repeating organization of the polypeptide chain. c. Tertiary structure: Tertiary structure is the entire three-dimensional shape of the protein. This shape is determined by the sequence of amino acids. In fact, a single change can change the entire structure. Tertiary structure is defined as any irregular loops or bends in the polypeptide chain and is typical of globular protein structure. d. Quaternary structure: The highest type of the protein structure called quaternary refers to the subunit structure of proteins. Proteins that have more than one polypeptide chain may also have more than one independently folded unit, each of at least on chain. The independently folded units are called subunits. The manner in which subunits are arranged to form the intact functional protein is called the quaternary structure. Functions of protein 1. Enzymes are proteins that aid the thousands of biochemical reactions taking place within and outside of the cells. 2. Some proteins are hormones, which are chemical messengers that aid communication between your cells, tissues and organs. 3. Some proteins are enzymes, which catalyse the chemical reactions. 4. Protein contains four calories per gram, the same amount of energy that carbohydrates provide. Fats supply energy as nine calories per gram. 5. Growth, maintenance and repairing of the cells. 6. The structural proteins which forms various structures of the cell. UTTARAKHAND OPEN UNIVERSITY Page 34 CELL BIOLOGY OF PLANTS MSCBOT-506 1.5.2.4. Nucleic acids The nucleic acids are the complex macromolecular organic compounds of immense biological importance. They control the important biosynthetic activities of the cells and carry hereditary information from generations to generations. There are two type of nucleic acids in animal as well as in the plant cells viz., deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Both are the polymers of nucleotides. A nucleotide is composed of nucleoside and phosphoric acid. Even the nucleoside is composed of the pentose sugar and nitrogen based (purines or pyrimidines). The purines are adenine and guanine and the pyrimidines are the cytosine, thymine and uracil. The cytoplasmic matrix contains only RNA, while DNA exclusively remains concentrated in the nucleus. The DNA and RNA almost have the similar chemical compositions except few differences (Fig. 1.11). Fig. 1.11: Structure of DNA and RNA (Nucleic acids) Functions of nucleic acids 1. Nucleic acids play an essential role in mitosis and meiosis. 2. Certain sections of nitrogenous bases along the strand of DNA form a gene which contain genetic information or codes for a particular product and transmits hereditary information to the next generation. In simple words, nucleic acids are reserve bank of genetic information. 3. Nucleic acids are the basic information pathway and control the cellular function of the organisms. 4. Responsible for the maintaining the identity of different species of organisms over millions of years. UTTARAKHAND OPEN UNIVERSITY Page 35 CELL BIOLOGY OF PLANTS MSCBOT-506 1.6 SUMMARY  The cell is a unit of biological activity delimited by a semipermeable membrane and capable of self-reproduction in a medium free of other living systems.  Cells emerged on the Earth at least 3.5 billion years ago.  Collectively, all the living cells are broadly classified into two category i.e., prokaryotic cells and eukaryotic cells, according to whether their genetic materials are enclosed by a nuclear envelope or not.  The shape may vary with animal to animal or organ to organ. Even the cells of the same organ may display variations in the shapes.  Typically the animal cell is spherical in shape but irregular, cylindrical, cuboidal, triangular, tubular, polygonal, oval, round elongated etc have also been seen in different organisms. Some cells (Amaeba and leucocytes) are able to change their body shape very frequently.  Generally, the eukaryotic cells are microscopic in nature but some animals and plant cells are easily visible by the necked eyes. For example, the egg of ostrich is the largest cell in the diameter and some nerve cells are considered more than 3-5 feet in length. Usually, the size of cells may vary between 1µm and 175000 µm (175 mm).  The numbers of the cells in particular organisms depend upon the size of the organisms. Larger size has the great number of the cells in its body.  The animal and plant cells are different from each other. The plant cells possess cell wall containing cellulose, hemicelluloses and pectin and large vacuole that regulates turgor pressure and allows plants to grow tall, while animal cell do not.  The cell provides the structure and protection to the cell.  The plasma it is selectively permeable to ions and organic molecules and thus regulates the movement of substances in the cells.  The cytoplasm conducts various vital activities of life.  The microtubules help and support in transportation to the cell.  Plastids are the characteristic features of the plant cell. They functions specially for the storage of starch, lipids and proteins, therefore, they are called amyloplasts, lipoplasts and proteinoplasts, respectively.  The green coloured plastid is known as chloroplast which helps in the biosynthesis of food by the process of photosynthesis.  Mitochondria are called the power house of the cell which provides the energy to conduct the various vital activities of the cell.  Endoplasmic reticulum provides the mechanical support to the cell and sites for a number of enzymes and cytochromes to carry out specific reactions.  Golgi complex carries out the processing of proteins generated in endoplasmic reticulum and also transports protein to the different parts of cell. UTTARAKHAND OPEN UNIVERSITY Page 36 CELL BIOLOGY OF PLANTS MSCBOT-506  Cytoplasmic vacuole is also the characteristic feature of the plant cell. Vacuoles are important in autophagy, store and help the digested food, contain water, phenol, flavonols, anthocyanins, alkaloids, and stored product such as sugar and proteins.  Ribosomes are the site of protein synthesis.  Nucleus controls all the functions of the cell. It regulates the heredity characters, synthesis of particular enzymes, responsible for protein synthesis, cell division, growth and differentiation.  Many specialized cells are present in plants which makes them unique from others. For example, in plants, cell wall is the prominent distinguishing features of the different kinds of specialized cells.  For the suitability, the specialized cell types in plant may be divided into three; Ground tissue system, dermal tissue system and vascular tissue system.  The chemical composition of the cell can be categorized into two parts viz., inorganic compounds and organic compounds.  The inorganic compounds normally occur in physical, non living universe such as elements, metals, non metals and its compounds like water, salts and the verities of the electrolytes and non electrolytes.  Water is the best solvent and plays a major role in the biochemical rections.  The chemical substance which contain the carbon in combination with one or more other elements as hydrogen, nitrogen, sulphur etc are called organic compound.  Carbohydrates can be represented by the stoichiometric formula (CH2O)n, where n is the number (at least 3) or CnH2nOn.  Carbohydrate functions as the main structural elements in plants in two forms i.e., cellulose and hemicellulose. Cellulose, a polysaccharide, is used to build the cell wall.  The lipids are the organic compound which are insoluble in water, whereas, soluable in organic compound (chloroform, ether, alcohol, benzene and other organic compound).  The lipids are important constituents of the cellular membrane, hormones and vitamins of the cells.  Proteins are very large molecules (macro-biopolymers) made from monomers called amino acids.  Proteins play a crucial role in the various biochemical activities of the cell.  The nucleic acids are the complex macromolecular organic compounds of immense biological importance. They control the important biosynthetic activities of the cells and carry hereditary information from generation to generations.  Nucleic acids play an essential role in mitosis and meiosis.  Nucleic acids are the basic information pathway and control the cellular function of the organisms.  Nucleic acid carried the genetic information to generation to generation. UTTARAKHAND OPEN UNIVERSITY Page 37 CELL BIOLOGY OF PLANTS MSCBOT-506 1.7 GLOSSARY Amyloplast: Organelle found in some plant cells that helps store and synthesize starch. When a plant is in need of energy, amyloplasts can also convert its starch back into sugar for food. Many amyloplasts can be found in starchy plants like potato tubers. ATP: Adenosine triphosphate. An adenine molecule, or a nucleotide, attached to three linearly connected phosphate groups (–H2PO4R, where R is a functional group). ATP basically shuffles energy around to support metabolism and a bunch of super important cellular processes, like photosynthesis. Cell Membrane: A thin semi-permeable membrane that surrounds the cytoplasm of a cell. Cell theory: The scientifically supported idea that the basic structural unit of life is the cell and that all cells arise from other cells. Cell wall: A rigid, but often flexible, layer containing cellulose or chitin, pectin, and other polymers. The cell wall is the outermost structure of plant, algal, fungal, and some prokaryotic cells. Centriole: A tubular structure that is made of protein and found only in animal cells. It is involved in cell division and the formation of flagella and cilia. Chloroplast: The organelle (see definition; think "mini organ") in plant cells, and a few other eukaryotic cells, which contains chlorophyll, the magical green pigment, and carries out the process of photosynthesis. Chromatin: The mass of genetic material composed of DNA and proteins that condense to form chromosomes during eukaryotic cell division. Chromosome: A long, stringy aggregate of genes that carries heredity information (DNA) and is formed from condensed chromatin. Cilia and Flagella: A rotrusions from some cells that aid in cellular locomotion. Collenchyma: Tissue composed of cells with unevenly thickened walls. Cytoplasm: All of the contents outside of the nucleus and enclosed within the cell membrane of a cell. Cytoplasm: The cytosol (fluid inside cells), organelles (except the nucleus), and other particles enclosed within the cell membrane. The cytoplasm is the site of most cellular activities, including glycolysis, production of energy from carbohydrates, and cell division, or the way cells reproduce. Cytoskeleton: A network of fibers throughout the cell's cytoplasm that helps the cell maintain its shape and gives support to the cell. UTTARAKHAND OPEN UNIVERSITY Page 38 CELL BIOLOGY OF PLANTS MSCBOT-506 Cytosol: The fluid component of the cytoplasm (collective name for the stuff within the boundaries of the cell membrane) composed of cytoskeleton filaments, dissolved molecules, and water. The cytosol is the part of the cytoplasm between the cell membrane and organelle membranes. DNA: Deoxyribonucleic acid. DNA is a macromolecule ("macro" = big) also known as a nucleic acid that is composed of phosphate groups, deoxyribose sugar groups, and the nucleotides adenine, guanine, cytosine, and thymine. DNA contains the genetic code needed by all cells to produce proteins and other molecules necessary to sustain life. He seems to make into every one of Shmoop's Biology glossaries. Endoplasmic Reticulum: A network of tubules and flattened sacs that serve a variety of functions in the cell. Enzymes: A protein that catalyzes, or increases the rate of, a chemical reaction in a cell. Eukaryote: An organism whose cells contain a membrane-bound nucleus. Flagellum: A protrusion of the cell membrane in some eukaryotic and prokaryotic cells that spins or lashes back and forth to aid in cellular locomotion. Genes: Segments of DNA located on chromosomes that exist in alternative forms called alleles. Genome: All of an organism's heredity information encoded in either DNA or RNA. Golgi body: An organelle in eukaryotic cells containing between three and seven flattened membrane disks called cisternae. The Golgi body packages and processes proteins and lipids, and is also called the "Golgi apparatus." Histone: Large protein complexes that control the messages sent from the DNA to the rest of the cell. Lysosome: A spherical, membrane-bound organelle in eukaryotic cells that contains enzymes (catalysts) and other proteins that digests, or break down, substances that have been taken into a cell by phagocytosis. Meiosis: A two-part cell division process in organisms that sexually reproduces, resulting in gametes with one-half the number of chromosomes of the parent cell. Microtubules: Fibrous, hollow rods that function primarily to help support and shape the cell. Mitochondrion (plural mitochondria): A membrane-bound organelle that provide the usable energy (in the form of ATP) from lipids, sugars, and proteins in a process known as cellular respiration. The mitochondrion is the cell's powerhouse. Mitosis: A phase of the cell cycle that involves the separation of nuclear chromosomes followed by cytokinesis. Nucleus: A membrane-bound structure that contains the cell's hereditary information and controls the cell's growth and reproduction. UTTARAKHAND OPEN UNIVERSITY Page 39 CELL BIOLOGY OF PLANTS MSCBOT-506 Organelles: Tiny cellular structures, that carries out specific functions necessary for normal cellular operation. E.g., Golgi bodies, lysosomes, mitochondria, chloroplasts, endoplasmic reticulum, vacuoles, and vesicles. Plant Cells: Eukaryotic cells that contain various membrane-bound organelles. They are distinct from animal cells, containing various structures not found in animal cells. Plasma membrane: A phospholipid (see previous definition) bilayer separating the interior of a cell from the surrounding environment. The membrane does lots of stuff, including protecting the cell, transporting materials into and out of the cell, and helping the cell communicate to other cells. Polar Fibers: Spindle fibers that extend from the two poles of a dividing cell. Prokaryote: An organism whose cells lack nuclei and membrane-bound organelles. Prokaryotes are generally single-celled. Prokaryotes: Single-celled organisms that are the earliest and most primitive forms of life on earth. Protein: A chain, or chains, of amino acids specifically folded to take on a certain shape, one that determines the protein‘s function. Ribosome: A complex structure made of proteins and ribosomal RNA, or rRNA. Ribosomes are found in all cells, both prokaryotic and eukaryotic. Together with messenger RNA (mRNA) and transfer RNA (tRNA), ribosomes synthesize proteins from amino acids (the building blocks of proteins). Ribosomes are not generally considered organelles because they are not membrane-bound. RNA: Ribonucleic acid. RNA is a macromolecule composed of phosphate groups (aka – H2PO4R, where R is a functional group), ribose sugars, and the nucleotides adenine, guanine, cytosine, and uracil. Rough endoplasmic reticulum (RER): A highly membranous organelle in eukaryotic cells, with a membrane-bound nucleus, dotted with ribosomes. The dots inspired the "rough" part of the name. The RER is the major site of protein synthesis. Schlerenchyma: Tissue composed of thick-walled cells containing lignin for strength and support. Sclereid: A type of schlerenchyma, made up of gritty cells, often called "stone cells." Sieve element: Cell in the phloem tissue concerned with longitudinal conduction of food materials. In flowering plants, it is called a sieve-tube element. Sieve tube: A series of sieve-tube elements arranged end to end and interconnected through sieve plates. UTTARAKHAND OPEN UNIVERSITY Page 40 CELL BIOLOGY OF PLANTS MSCBOT-506 Smooth endoplasmic reticulum (SER): A highly membranous organelle in eukaryotic cells that is not associated with ribosomes. The SER is the major site of lipid and steroid synthesis, and is continuous with the nuclear membrane and rough endoplasmic reticulum, or RER. Stroma: Dense fluid found between grana (stacks of thylakoid disks) of a plant cell's chloroplast. Stroma is where carbohydrate forming reactions occur during photosynthesis. Vacuole: A large, membrane-bound organelle found in most plant and fungal cells, as well as some animal and bacterial cells. The vacuole's job varies with cell type, but in many cases, the vacuole is involved in water regulation, waste removal, and pH balance within the cell. Vesicle: A small, sac-like organelle involved in the transport and storage of cellular substances, especially proteins marked for secretion from the cell. Vessel element: Individual cells that make up vessels. Vessel: A tube-like series of vessel elements with open ends. The walls that join the members have perforations or holes in them to allow water to pass through freely. Xylem: The water-conducting tissue of a vascular plant. Minerals are also transported through the xylem. 1.8 SELF ASSESSMENT QUESTIONS 1.8.1 Multiple Choice Questions: 1. Name an organelle which serves as a primary packaging area for molecules that will be distributed throughout the cell? (a) Mitochondria (b) Golgi apparatus (c) Vacuole (d) None 2. Which among the following sentences is not correct about the organelles? (a) They are found in multicellular organisms. (b) They are found in all Eukaryotic cells. (c) They are small sized and mostly internal. (d) They coordinate to produce the cell. 3. Blue green Algae are: (a) Eukaryotic (b) Prokaryotic (c) Neither a nor b (d) Both a or b 4. Which of the followings has a perforated cell wall? (a) Vessel (b) Fibre (c) Tracheid (d) Sclereid UTTARAKHAND OPEN UNIVERSITY Page 41 CELL BIOLOGY OF PLANTS MSCBOT-506 5. Fibres associated with phloem (a) Wood fibres (b) Bast fibres (c) Hard fibres (d) Surface fibres 6. Collenchyma occurs in (a) Herbaceous climbers (b) Woody climbers (c) Climbing stems (d) Water plants 7. Which biomolecule is distributed more widely in a cell? (a) Chloroplast (b) RNA (c) DNA (d) Spaherosomes 8. Which is a reducing sugar? (a) Galactose (b) Gluconic acid (c) Sucrose (d) None of the above 9. Which of the following is a phospholipid? (a) Sterol (b) Cholesterol (c) Lecithin (d) Steroid 10. RNA does not possess (a) Uracil (b) Thymine (c) Adenine (d) Cytosine 1.8.2 Fill in the blanks: 1. Cell "building blocks of life" is the ………….. unit of all organisms. 2. The cell was first discovered by ……….. in year ……….. 3. Prokaryotic cells may be defined as the cells which do not have a …….. and …….. organelles. 4. PPLOs are free living organisms and do not required host cell for ……….. 5. The bacterial cytoplasm is a ……….. and ……….. material. 6. Certain bacteria are able to do photosynthesis with the help of a pigment called …………. 7. In a eukaryotic cell ………… is a reticulated organelle of the cytoplasm. 8. …………. are the living, generalized, multipurpose, thin walled cells and range from spherical to barrel-like in shape. 9. ………… is the most abundant inorganic compound of the cell and constitute about 70-80% of the matrix. 10. ….. are very large molecules (macro-biopolymers) made from monomers called amino acids. 1.8.3 True and False: 1. Many bacteria are able to swim freely with the help of thread like structure called flagella. 2. Some bacteria also possess a hair like out growth called pili or fimbriae. 3. The word trichomes is derived from a Greek word meaning hair. UTTARAKHAND OPEN UNIVERSITY Page 42 CELL BIOLOGY OF PLANTS MSCBOT-506 4. The eukaryotic cells do not contain a well-constructed nucleus (nucleus enclosed within the membrane) and membrane bounded cell organelles. 5. Animal cells true have a cell wall. 6. Vessel elements have perforation plates that connect each vessel element to form one continuous vessel. 7. The cytoplasm of animal cell possesses numerous membrane-bound organelle originated from the Golgi complex is called lysosomes. 8. The sclerenchyma cells are dead, elongated, rigid, heavily thickened secondary walls containing lignified cells. 9. Carbohydrates can be represented by the stoichiometric formula (C2H4O)n. 10. The lipids are the organic compound which are soluble in water whereas insoluble in organic compound. 1.8.1 Answers Key: 1(b); 2(a); 3(b); 4(a); 5(b); 6(c); 7(b); 8(a); 9(c); 10(b) 1.8.2 Answers Key: 1. Smallest; 2. Robert Hooke 1665; 3. True nucleus, membrane-bound; 4. Duplication, 5. Viscous, dense, colloidal and granulated; 6. Bacteriochlorophyll; 7. Endoplasmic reticulum (ER); 8.Parenchyma; 9.Water; 10. Proteins 1.8.3 Answers Key: 1. True; 2. True; 3. True; 4. False; 5. False; 6. True; 7. True; 8. True; 9. False; 10. False 1.9 REFERENCES  Campbell NA, Williamson B, Heyden RJ (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 978-0-13-250882-7.  Gunning PW, Ghoshdastider U, Whitaker S, Popp D, Robinson RC (2015). The evolution of compositionally and functionally distinct actin filaments. Journal of Cell Science. 128 (11): 2009–19. doi:10.1242/jcs.165563. PMID 25788699.  Koch AL (2003) Bacterial wall as target for attack: past, present, and future research. Clinical Microbiology Reviews. 16 (4): 673–87.  Maitland Jr J (1998). Organic Chemistry. W W Norton & Co Inc (Np). p. 139. ISBN 978-0- 393-97378-5.  Nelson DL, Cox MM (2005) Lehninger Principles of Biochemistry (4th ed.). New York: W.H. Freeman. ISBN 978-0-7167-4339-2.  Slabaugh, M R.; Seager, S L. (2013). Organic and Biochemistry for Today (6th ed.). Pacific Grove: Brooks Cole. ISBN 978-1-133-60514-0.  Van Heijenoort J (2001) Formation of the glycan chains in the synthesis of bacterial peptidoglycan. Glycobiology. 11(3):25R36R. doi:10.1093/glycob/11.3.25R. PMID 11320055  Verma PS, Agarwal VK (2008) Cytology: Cell biology and molecular biology. S. Chand & company Ltd. Ramnagar, New Delhi. UTTARAKHAND OPEN UNIVERSITY Page 43 CELL BIOLOGY OF PLANTS MSCBOT-506  Weiler EW, Nover L (2008). Allgemeine und Molekulare Botanik (in German). Stuttgart: Georg Thieme Verlag. p. 532. ISBN 978-3-13-152791-2.  Whitman WB, Coleman DC, Wiebe WJ (1998) Prokaryotes: The unseen majority. Proceedings of the National Academy of Sciences of the United States of America. 95 (12): 6578–6583. 1.10 SUGGESTED READINGS  Campbell NA, Williamson B, Heyden RJ (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 978-0-13-250882-7.  Nelson DL, Cox MM (2005) Lehninger Principles of Biochemistry (4th ed.). New York: W.H. Freeman. ISBN 978-0-7167-4339-2.  Verma PS, Agarwal VK (2008) Cytology: Cell biology and molecular biology. S. Chand & company Ltd. Ramnagar, New Delhi. 1.11 TERMINAL QUESTIONS 1.11.1 Short answer type questions: 1. What are difference between prokaryotic cells and eukaryotic cells? 2. Write the differences between animal