Cellulose Diagnostic Quiz PDF

Introduction to Cellulose FPU 192 Chemistry of Forest Products  Diagnostic Quiz Please choose the letter of the correct answer.  Test your knowledge on Cellulose 1. Which of the following elements cannot be found in cellulose? D Nitrogen  Test your knowledge...

Introduction to Cellulose FPU 192 Chemistry of Forest Products  Diagnostic Quiz Please choose the letter of the correct answer.  Test your knowledge on Cellulose 1. Which of the following elements cannot be found in cellulose? D Nitrogen  Test your knowledge on Cellulose 2. The molar mass of cellulose in g/mol is: D 172. 14  Test your knowledge on Cellulose 3. The density of cellulose in g/cm3 is: D 2.5  Test your knowledge on Cellulose 4. What is the melting point of cellulose in degrees Celsius? D 350  Test your knowledge on Cellulose 5. What is the color of cellulose? D Colorless  Cellulose – (C6H12O6)n What is Cellulose? Cellulose is the most abundant organic compound on earth It is a complex carbohydrate consisting of oxygen, carbon, and hydrogen It is chiral, tasteless and has no odor First discovery of cellulose was in the year 1838 – [French chemist by name Anselme Payen ] It is an organic compound and is water-soluble and biodegradable.  Cellulose – (C6H12O6)n  During the year 1980 it was used as to produce the first thermoplastic called celluloid.  Properties of Cellulose Majority of the properties of cellulose depend upon the degree of polymerization or chain length and the number of glucose molecules constituting the polymer molecule.  Monomer vs. Polymer Monomer Polymer comes from mono- (one) and - comes from poly- (many) and - mer (part) mer (part) small molecules which may be may be a natural or synthetic joined together in a repeating macromolecule comprised of fashion to form more complex repeating units of a smaller molecules called polymers molecule (monomers)  Cellulose  the most abundant organic (containing carbon) molecule on the planet due to its presence in plant cell walls and its slow rate of breakdown in nature  structurally strong  different from starch and glycogen as it is not a polymer of alpha glucose, but of beta D-glucose  Cellulose  Polysaccharide of glucose units in unbranched chains with ß-1,4,- glycosidic bonds  cannot form hydrogen bonds with water; thus, it is insoluble in water  cannot be digested by humans because humans cannot break down ß-1,4,- glycosidic bonds  Kind of Sugars  they come under the category of carbohydrates 3 Kinds of Sugar 1. Monosaccharide - contain just one molecule (ex. Dextrose, Glucose, Fructose and Galactose) 2. Disaccharide - complex structure of sugars (ex. Sucrose and maltose) 3. Polysaccharides - major classes of biomolecules; long chains of carbohydrate molecules, composed of several smaller monosaccharides (ex. starches and cellulose) Kind of Sugars Alpha glucose vs. Beta glucose In the structure of Alpha glucose, the orientation is (1- hydroxyl) and (4-hydroxyl). These both get connected at the same side of the carbon atom. In case of Beta glucose, the orientation is again the (1- hydroxyl) and (4-hydroxyl) , but this time, these both get connected with the carbon atom at the opposite sides of each other. So, both the glucose, alpha glucose and beta glucose have the same structure, just the orientation of the hydroxyl group is different.  Formation and Location of Cellulose in the Cell Wall  synthesized at the plasma membrane (PM) and organized into micro-fibrils  plant cell walls is made up of cellulose molecules arranged to form microfibrils  number of combined microfibrils is needed to form a cellulose fiber  cellulose microfibril are 5 to 12 mm wide  microfibrils contain 20 to 40 individual chains  Cellulose Structure  made up of long unbranched chain of atleast 500 b- D- glucose molecules  this are linked with each other by B-1-4 glycosidic linkage  with inverted glucose residue  Reactions of Cellulose Cellulolysis - process of cellulose degradation - can be discussed through: hydrolysis, decomposition (microbial) and heat  Hydrolysis Acid based solutions  Hydrolysis Reactions happening during breakdown: - main monomer that composes cellulose is glucose INTERMIDIATE UNITS THAT ARE MADE FROM CELLULOSE 1.Cellobiose - when two glucose molecules are connected (ex. maltose) 2. Cellotriose - When three glucose units are connected (ex. β - D pyranose form) 3.Cellotetraose - four glucose units connected together  Cellobiose Figure 1. : Cellobiose, or maltose (glucose + glucose) chemical structure. Credit: Maltose Haworth: from Wikimedia Commons Cellotriose Figure 2: Cellotriose in the β-D-pyranose form. Credit: Answers.com Cellotriose Figure 3.: Cellotetraose. Credit: Green Chem., 2012,14, 1284-1288 Endocellulose - breaking down the crystallinity in the cellulose to an amorphous strand Exocellulases- hydrolysis of the chain ends to break the polymer into smaller sugars; products are typically cellobiose and cellotetraose β-glucosidases- the disaccharides and tetrasaccharides (cellobiose and cellotetraose) are hydrolyzed to form glucose  Hydrolysis Acid based solutions  Microbial (Enzymatic) Enzymes Microbial (Enzymatic) Microbial (Enzymatic)  Figure A The three primary constituents of biomass. Biomass is primarily composed of a combination of (A) cellulose—a homopolymer of glucose units, (B) hemicellulose (here depicted as xylan—a homopolymer of xylose units), and (C) lignin (here depicted as hardwood lignin)—a biopolymer composed of aromatic monomeric units. As these components are degraded (D) their fermentable breakdown products are shuttled into bacterial cells via ATP binding cassette transporter proteins and internally converted to glucose-1- phosphate (G1P). G1P is utilized in a modified form of glycolysis that produces pyruvate, which is then broken down into lactate and formate, or converted to acetyl-CoA and further Source: Akinosho et. al., 2014 metabolized to acetate and ethanol.  Microbial (Enzymatic) Cellulolysis Fermentation Process Explanations Do C5 and C6 sugars need to be fermented separately? Zymomonas mobilis (Z. mobilis) – bacterium that converts sugars to pyruvate, which is then fermented to ethanol and carbon dioxide Saccharomyces cerevisiae – bakers yeast used in brewery industry to produce ethanol from C6 sugars Escherichia coli – (E. coli) uses mixed-acid fermentation in anaerobic conditions, producing organic acid (lactate, succinate, acetate, and formate) and ethanol acetate and carbon dioxide Image Source: Springer Link  Thermolysis  means the breakdown of cellulose when it is exposed to high temperature or heat Thermolysis of cellulose occurs at 350 degrees, when decomposes into vapors of carbon dioxide and other aerosols. This temperature is called thermolytic temperature or pyrolytic temperature. Pyrolytic/Pyrolysis - process of decomposition of various compounds or materials with thermal decomposition at temperatures around 400–800°C in an oxygen-free atmosphere or contain very small amount of oxygen Cellulose - Derivative  Acetate Compound CA - syntheticcompound derived from the acetylation of the plant substance cellulose - commonly prepared by treating cellulose with acetic acid and - In unaltered cellulose, the X in the molecular structure then with acetic anhydride in the represents hydrogen (H), indicating the presence in the molecule of presence of a catalyst such as three hydroxyl (OH) groups. The OH groups form strong hydrogen bonds between cellulose molecules, with the result that cellulose structures sulfuric acid. cannot be loosened by heat or solvents without causing chemical decomposition. However, upon acetylation, the hydrogen in the hydroxyl groups is replaced by acetyl groups (CH3-CO). The resultant cellulose acetate compound can be dissolved in certain solvents or softened or melted under heat, allowing the material to be spun into fibres, molded into solid objects, or cast as a film.  Acetate Compound Propionate CAP CHEMICAL FROMULA - C76H114O49 - a cellulose ester wherein some of three hydroxyl groups of a cellulose unit (glucose combined with β1-4 glycoside bond) are substituted with acetyl and propionyl - can be synthesized by using an acid anhydride or an acid chloride as an acylating agent  Acetate Compound Propionate CAP CHEMICAL FROMULA - C76H114O49 - Excellent solubility, structural stability, light and weather resistance, good leveling, high gloss retention, good transparency. (Huang et. al., 2011) - They are widely used in the paint industry for top grade cars and furniture, as well as printing ink.  Acetate Compound Butyrate CAB CHEMICAL FROMULA - [C6H7O2-(OCOCH3)X-(OCOC3H7)Y-(OH)3-X-Y]n, - a mixed ester thermoplastic derivative of cellulose acetate that contains both acetate and butyrate functional groups. - It has improved weathering resistance and lower moisture absorption compared to cellulose acetate - it was designed for use where low- application viscosities at relatively high solids levels is needed. It is soluble in a wide range of solvents and compatible with many other resins  Acetate Compound Butyrate CAB CHEMICAL FROMULA - [C6H7O2-(OCOCH3)X-(OCOC3H7)Y-(OH)3-X-Y]n, - the structure of cellulose ester, hydroxyl groups are co-esterified with acetic acid and butyric acid - contains about 12–15% (wt %) of acetyl groups and 26–39% (wt %) of butyryl groups, which endows it with excellent physical and chemical properties including outstanding moisture resistance, UV resistance, temperature resistance, flexibility, transparency, etc  Carboxymethyl cellulose (CMC) CHEMICAL FROMULA - C8H15NaO8 - also known as cellulose gum - soluble in water at any temperature because of its highly hygroscopic nature, CMC hydrates rapidly - is a cellulose derivative with carboxymethyl groups (-CH2-COOH) bound to some of the hydroxyl groups of the glucopyranose monomers  Carboxymethyl cellulose (CMC) CHEMICAL FROMULA - C8H15NaO8 - used as a viscosity modifier or thickener, and to stabilize emulsions in various products, both food and non-food. - it is used primarily because it has high viscosity, is nontoxic, and is generally considered to be hypoallergenic, as the major source fiber is either softwood pulp or cotton linter - Non-food products include products such as toothpaste, laxatives, diet pills, water-based paints, detergents, textile sizing, reusable heat packs, various paper products, and also in leather crafting to help burnish edges  Ethyl Cellulose (EC) CHEMICAL FROMULA - - a derivative of cellulose in which some of the hydroxyl groups on the repeating glucose units are converted into ethyl ether groups - mainly used as a thin-film coating material for coating paper, vitamin and medical pills, and for thickeners in cosmetics and in industrial processes FPU 192 CHEMISTY OF FOREST FRODUCTS OBJECTIVE: At the end of the lesson, the students should be able to appreciate the importance of chemistry to forestry and define terminologies related to chemistry of forest products. CONCEPTS:  the country has a high demand in wood consumption but has low production  the country needed 6 million cubic meters of wood annually  25% of the national demand comes from local resources while 75% is imported CONCEPTS:  charcoal and fuelwood has one of the highest demands especially in households, industrial and commercial use  [PEP] wood waste is accounted 44 percent of the over-all NRE estimates of the country  [44 %] wood waste is shared among: household, industrial/commercial and grid electricity sectors CONCEPTS:  this course explores the chemistry of wood products, its preservation etc. IMPORTANCE:  cellulose and hemicellulose are known to be composed of polysaccharides; lignin is oxygenated polymer of phenylpropane units  to know other components of wood viable for chemical processes turning them into something useful Source: Quara IMPORTANCE:  e.g. extractives  inorganic ash contents (0.1 – 0.3% by weight and rarely exceeds 0.5%) Source: Quara  OTHER ROLE OF CHEMISTY IN FORESTRY?  we understand the plant anatomy, use of organic chemical, biochemical and the physiological processes of plants for efficient management of the forest resources help us to know how photosynthesis take place, how sunlight and water taken by the tree is use to make food help in the area of medicine, through chemical test we know medicine that heal different type of disease through chemistry in forestry we know how the chemical energy flow in the ecosystem IMPORTANCE: Scope of this, is how are we going to utilize chemicals to be a useful, necessary tools for helping to meet needs for food, wood fiber, and water, while man readjusts his numbers and modes of life to the rapidly dwindling resources of the earth. The more selective, less persistent chemicals will continue to play an important role in forest resource management, probably for several decades. However, chemical use must eventually be minimized, for it is simply a system of treating symptoms of unhealthy ecological conditions created by nature or man in the past (Tarrant et al., 1973). TERMS: CHEMISTRY - a branch of natural science that deals principally with the properties of substances, the changes they undergo, and the natural laws that describe these changes (uidaho.edu, 2022)  involves the study of the atomic composition and structural architecture of substances, as well as the varied interactions among substances that can lead to sudden, often violent reactions (britannica.com, 2022) TERMS: WOOD CHEMISTRY – is the study of the chemical components and characteristics of wood. CLASSIFICATION OF FOREST PRODUCTS FOREST PRODUCTS - Goods and services derived from the forest such as but not limited to timber, lumber, veneer, plywood, fiberboard, pulpwood, firewood, bark, tree top, resin gum, wood oil, honey, beeswax, nipa, rattan or other forest growth such as grass, shrub and flowering plant, the associated water, fish, game, scenic, historical, and educational (DAO. 1987-80, 1987).  CLASSIFICATION OF FOREST PRODUCTS Forest Products Classification: 1. MAJOR FOREST PRODUCTS - Comprises Timber and Fuel wood. Fuelwood, Log, Lumber, Plywood, Veneer, Non-timber forest products, Blackboard (DENR-FMB). a.1. Primary Wood Products are those products use in raw form. Ex. Logs, poles, piles, post, mine timber, railroad ties.  CLASSIFICATION OF FOREST PRODUCTS Forest Products Classification: a.2. Secondary Wood products are those products that undergone further remanufacturing. a.2.1. Mechanically reduced wood products – These are reduced using machines or mechanical means. Ex. Wooden chairs, cabinets, veneers, crates etc. a.2.2. Physically reduced wood products – This are wood products derived by applying heat on wood like charcoal, (product of carbonization), wood tar and alcohol product of distillation. a.2.3. Chemically reduced wood products – They are results of applying chemical methods of processing wood. Examples are pulp and paper, fiberboard, and cellulosed-derived products.  CLASSIFICATION OF FOREST PRODUCTS Forest Products Classification: 2. MINOR FOREST PRODUCTS - Forest usufructs obtained from fruits, flowers, leaves, twigs, bark, root and wood of plants (except timber) and other products from animal and mineral origins (DENR-FASPS, 2020.  CLASSIFICATION OF FOREST PRODUCTS Forest Products Classification: EXTRACTIVES - non-structural components of wood b.1. Tree exudents - natural discharges of living trees and other forest growths induced by a natural or inflicted wound on the plant A. RESINS - Manila copal (almaciga), dammar (dipterocarp) and balau (apitong, Manila Elemi (“brea blanca) or white pitch Source: https://en.wikipedia.org/wiki/Dammar_gum Manila Copal “MANILA ELEMI” B. GUMS – eucalyptus, acacia species, cherry and plum trees C. SAPS – Moraceae species D. LATEX - chicle, rubber, and gutta-percha b. 2. Extracted Products – chemically derived or reduced a. dyes b. Tannins - from mangrove species, oak species, sakat and camatchile c. naval stores – Obtained from pine species, distillation of resin produce gum turpentine and gum resin. d. essential oils ex. Olive oil, Non-timber Forest Products - All biological materials and derivatives other than timber, which are extracted from forests for human use. Synonymous to Non-wood forest products (DENR-FMB, 2004). a. bamboo b. rattan (split and unsplit) c. nipa shingles d. medicinal plants e. fibrous plants (bast fibers) Fibers from inner bark f. leaves, fruits and vines g. animal-based products (horns, fur, etc.) e. other NTFPs not listed  FPU 192 Chemistry of Forest Products Chapter 2 The Wood Objectives: At the end of the lesson, students should define and characterize the different chemical components of a wood. PLANT KINGDOM THALLOPHYTES BRYOPHYTES PTERIDOPHYTES SPERMATOPHYTES algae mosses and ferns seed-producing fungi liverworts plants bacteria Monocots ANGIOSPERMS flower-bearing CLASSES Dicots - produce timber called “hardwoods “ GYMNOSPERMS cone-bearing ORDERS CYCADALES Oliva and Pitogo GINKOALES Monotypic Single species Ginkgo biloba GNETALES FAMILIES CONIFERALES F. WELWITSCHIACEAE - produces timber of commercial scale (“softwoods “) F. EPHEDRACEAE - also collectively known as “conifers or evergreens ” F. GNETACEAE Figure ___. Taxonomic position of wood-producing vascular plants Plant Classification The plant kingdom is divided into: (1) Thallophytes - simplest plants; mostly unicellular; reproduce through cell division; includes bacteria, algae and fungi (2) Bryophytes - represented by mosses and liverworts. This group has chlorophyll but structure is of primitive type - meaning, they do not possess vascular tissues. (3) Pteridophytes - from the word "pteris" which means ferns. Their stems, roots and leaves possess vascular tissues but are small and short-lived, although many are considered perennials. Reproduction involves spore formation. (4) Spermatophytes - the seed-producing plants which consists of two major groups: a. Gymnosperms - cone-bearing; seeds are naked and leaves are mostly needle- like or acicular if not subulate. Represented by Benguet pine, Igem and Almaciga There are four recognized Orders of gymnosperms: (1) Cycadales - woody plants in the tropics resembling tree ferns and palms; e.g., oliva and pitogo (2) Gingkoales - monotype, restricted to a single species Gingko biloba of China and Japan, a deciduous tree with a habit of conifer and with fan- shaped leaves like the pinnae of the maiden-hair fern (hence the name "maiden-hair tree") (3) Gnetales - regarded as the most recent Order of the Gymnosperms in the phylogenetic sequence. It accordingly shows an intermediate position between the gymnosperms and the angiosperms. Vessels are found in angiosperms as conducting tissues and are not found in any other gymnosperm except in gnetales. There are three families under Order Gnetales: (a) Family Welwitschiaceae - monotype consisting of one genus and species, Welwitschia mirabilis. (b) Family Ephedraceae - single genus, Ephedra spp., a source of an alkaloid called "ephedrine" which is used as a substitute for adrenaline. (c) Family Gnetaceae - single genus, Gnetum, with 30 species of small trees and woody lianas found in tropical forests. (4) Coniferales - the only Order of the Gymnosperms capable of producing timber in commercial scale. Species under this group are collectively known as "conifers” or evergreen, cone-bearing trees which are source of the so-called "softwood lumber" in the wood industry. b. Angiosperms - flowering plants; seed enclosed in an ovary and most are broad- leaved; divided into two types: i) monocots - with single seed leaf and scattered vascular bundles; e.g., coconut  ii) dicots - two seed leaves with vascular tissues arranged in a ring form and also characterized by the presence of pith at the center of stem Structure of Plants Like animals, plants are multicellular eukaryotes whose bodies are composed of organs, tissues, and cells with highly specialized functions. The relationships between plant organs, tissues, and cell types are illustrated below. https://organismalbio.biosci.gatech.edu/growth-and-reproduction/plant-development-i-tissue-differentiation-and-function/ Figure 2. Plant Structure The stems and leaves together make up the shoot system. Each organ (roots, stems, and leaves) include all three tissue types (ground, vascular, and dermal). Different cell types comprise each tissue type, and the structure of each cell type influences the function of the tissue it comprises (Georgia Tech Biological Sciences, 2016). Plant Organ System In plants, just as in animals, similar cells working together form a tissue. When different types of tissues work together to perform a unique function, they form an organ; organs working together form organ systems. Vascular plants have two distinct organ systems: a shoot system and a root system. The shoot system consists of two portions: the vegetative (non- reproductive) parts of the plant, such as the leaves and the stems; and the reproductive parts of the plant, which include flowers and fruits. The shoot system generally grows above ground, where it absorbs the light needed for photosynthesis. The root system, which supports the plants and absorbs water and minerals, is usually underground (OpenStax College-Biology, 2013). Plant Tissues and Cells Plant tissues are characterized and classified according to their structure and function. The organs that they form will be organized into patterns within a plant which will aid in further classifying the plant. A good example of this is the three basic tissue patterns found in roots and stems which serve to delineate between woody dicot, herbaceous dicot and monocot plants (Biologyonline). 1. Dermal tissue covers and protects the plant, and controls gas exchange and water absorption (in roots). Dermal tissue of the stems and leaves is covered by a waxy cuticle that prevents evaporative water loss. Stomata are specialized pores that allow gas exchange through holes in the cuticle. Unlike the stem and leaves, the root epidermis is not covered by a waxy cuticle which would prevent absorption of water. Root hairs, which are extensions of root epidermal cells, increase the surface area of the root, greatly contributing to the absorption of water and minerals. Trichrome, or small hair-like or spikey outgrowths of epidermal tissue, may be present on the stem and leaves, and aid in defense against herbivores. https://www.toppr.com/guides/biology/anatomy-of-flowering- plants/tissue-systems/ Figure 3. Dermal Tissue 2. Ground tissue carries out different functions based on the cell type and location in the plant, and includes parenchyma (photosynthesis in the leaves, and storage in the roots), collenchyma (shoot support in areas of active growth), and sclerenchyma (shoot support in areas where growth has ceased) is the site of photosynthesis, provides a supporting matrix for the vascular tissue, provides structural support for the stem, and helps to store water and sugars. 3. Vascular tissue transports water, minerals, and sugars to different parts of the plant. Vascular tissue is made of two specialized conducting tissues: xylem and phloem. Xylem tissue transports water and nutrients from the roots to different parts of the plant, and also plays a role in structural support in the stem. Phloem tissue transports organic compounds from the site of photosynthesis to other parts of the plant. The xylem and phloem always lie adjacent to each other in a vascular bundle.  https://cpn-us- w2.wpmucdn.com/site Figure 4. Location of Plant Tissues in Different Plant Organ System. B. The Wood: A Renewable resource Wood refers to the solid part or the trunk of trees. It is the fibrous plant material largely composed of cellulose as the main framework of structure and lignin as the binder, or xylem portion of the stem (Abasolo, undated). Wood is the ultimate renewable resource it is primarily because it is abundant, renewable, and usable from bark to treetop for everything from homes and buildings to paper and energy production (NAFO, 2022). Gross Internal Structure of Stem/Wood Bark – outer part of the stem Cambium – found between the bark and the wood, a layer of meristematic cells responsible for the increase in diameter of the stem Cork cambium (phellogen) – outer part of the bark that produces cork cells Wood/xylem – inner part of the stem Pith – parenchymatous tissue inside the xylem Gross Physical Features of Wood A. Texture - refers to the size and proportional number of woody elements. Description of texture in relation to the size of wood pores may be of the following: (1) very fine - pores visible only with the aid of hand lens, e.g., Kamagong (2) fine - pores are just barely visible to the naked eyes, e.g., amugis (3) moderately coarse - pores readily visible to the naked eyes, e.g., ipil (4) coarse - pores are very distinct to the naked eyes, e.g., red lauan B. Color - due to the presence of extractives deposited in the wood cells. Color may be used to distinguish some wood species: (1) bright yellow or orange - bangkal and kalamansanai (2) light wine red to blood red – tindalo and narra (3) black or with black stripes - wood of Family Ebenaceae, such as kamagong and ebony (4) bright yellow when fresh, but become straw colored upon drying - woods of ipil and anubing C. Luster - the ability to reflect light. Some woods are lustrous as tindalo and almaciga while some are dull or non-lustrous like apitong and toog. D. Hardness - resistance to indentation. This may be known by cutting the sample with a knife or by applying pressure with the fingernails on the longitudinal surface of the wood. E. Weight - the weight of wood is dependent on three factors: (1) amount of wood substances (2) moisture content (3) amount of extractives present Some of the hardest and heaviest wood in the world are found in the Philippines. Mangkono (Xanthostemon verdugonianus) is the heaviest Philippine wood. Malabayabas and Mangkono of Family Myrtaceae are extremely heavy woods with basic specific gravity values at 0.923 and 1.043, respectively. Kapok, hamindang and malakalumpang are light woods (sp.gr. at 0.222, 0.291, and 0.270). F. Odor - some wood species give-off distinct odors which are efficient in distinguishing them from other specimens. Examples: (1) dungon - smells like old leather (2) tindalo - smells like fresh beans (3) Lauraceae species - with aromatic or fragrant odor (4) malatae (Celtis cinnamomea) - emits unpleasant odor (5) sawdusts of akle, akleng-parang and malugai are irritating to the nasal mucous membrane and can cause severe headache G. Taste - most Philippine wood species are tasteless but few species have distinct tastes like pagatpat which tastes salty and batino which has a bitter taste H. Grain direction - this refers to the arrangement/orientation of the wood elements with respect to respect to the longitudinal axis (1) straight-grained - almaciga, teak and malabulak (2) cross-grained - antipolo, anubing and most dipterocarp species (3) wavy-grained - liusin, amugis and bansalangin (4) spiral-grained - bagalunga and kalantas Structural Features of Wood A. Growth rings - distinct alternating light and dark bands of tissues encircling around the core/pith of wood. These represent the bands of growth increments of the tree every year and are differentiated as follows: (1) earlywood or springwood - lighter colored rings developed during the rainy seasons. Cells with thinner walls and of lower density. (2) latewood or summerwood - darker colored bands formed during the dry or summer season. Cells with thicker walls and of higher density. B. Vessels or Pores - a vessel is an axial series of cells that have fused to form a tube-like structure of indeterminate length. The cellular components of a vessel are known as vessel elements or members. The term "pore" is used to denote the cross section of a vessel. Diagnostic features which serve to describe vessels or pores are abundance or number; distribution; size; nature and extent of pitting; and the presence of inclusions or deposits. Pore size and arrangement is known as topography. Hardwoods can be grouped on the basis of pore size. If the pores are fairly uniform and quite evenly distributed throughout the growth rings, the wood is said to be diffused-porous and this is represented by a great majority of the hardwoods. If the pores formed at the start of the growth period are much larger than those farther out in the ring, the wood is ring-porous, as in narra, mahogany, teack, bagalunga and kalantas. C. Perforation Plate - a portion of the woody cell wall involved in the fusion of two members of a vessel which bears the perforation through which the vessel elements are interconnected. Types of Perforation Plates: (1) scalariform - with multiple perforations that are elongated and parallel, as in katmon (2) reticulate - with multiple perforations of net-like appearance, as in wood of marang (3) epheroid - with small group of large, circular openings (4) foraminate - with openings that are small, circular or polygonal in shape, as in pingka-pingkahan species D. Parenchyma - soft tissues of small and thin-walled cells mainly for storage and secondarily for food distribution. It is distinctly lighter in color than the surrounding tissues. Types of Parenchyma:  I. Apotracheal - associated with, or independent from the pores (1) marginal - associated with the edge of growth rings (a) Terminal - formed singly or in a continuous layer of variable width at the end of each growth period, e.g., woods of supa and malugai (b) Initial - formed singly or in a continuous layer of variable width at the onset of a growth period, e.g., woods of mahogany and kalantas (2) diffuse - distributed irregularly, e.g., falcata woods (3) banded - cells form concentric lines or bands separate from the pore arrangement, e.g., balete & tangisang-bayawak (4) diffuse-in-aggregates - cells are grouped in short tangential lines from ray to ray, e.g., kalalang species, also tindalo in apotracheal fine lines. II. Paratracheal - associated with the vessels or pores (1) vasicentric - forms a complete circular or slightly oval sheath of different width around a vessel. e.g., evident in leguminous woods like akleng-parang & rain tree (2) aliform - with wing-like lateral extensions; appears in some leguminous woods like tindalo & antsoan and some dipterocarp species of Shorea and Hopea (3) banded - cells form concentric lines or bands associated with teh vessels or pores, e.g., manggis & malaaduas (4) confluent - coalesced aliform-type in irregular tangential or diagonal bands seen in tindalo, kamatog and ipil woods E. Wood Rays - tissues concerned with transverse conduction of food and water; they are ribbon-like aggregate of cells formed by the vascular cambium arranged in horizontal rows and are quite uniform in height. Such arrangement is called storied, and appears as ripple marks when viewed with the naked eyes or lens. Types of vascular rays: (1) homocelllular ray - a xylem ray composed of cells of the same morphological type, e.g., all procumbent or all upright (2) heterocellular ray - a xylem ray composed of cells of different morphological types, e.g., procumbent cells and square or upright cells. Note: A procumbent ray cell is oriented with its main axis perpendicular to the axis (grain) of prosenchymatous elements when viewed in radial section. An upright ray cell is oriented with its main axis parallel to the axis of prosenchymatous elements when viewed in radial section. In radial section, square ray cells have more or less equidimensional sides. F. Tracheids - imperforate wood cells with bordered pits usually observed in tangential sections or in macerated woods. Types of hardwood tracheids with short fibrous cells: (1) Vasicentric tracheids - short, irregularly formed with conspicuous bordered pits near the vessel elements which do not form a definite axial row, as in Phil. mahogany  species (2) Vascular tracheids - specialized cells in certain hardwoods, similar in size, shape and position to small latewood vessel elements, except that they are imperforate at the ends. They are arranged in axial series like the nearby small vessels, their lateral walls are pitted and frequently have spiral thickenings Note: Softwoods consist mainly of tracheids which function as water conducting and supporting elements. They appear in cross sections in radial rows, usually square or polygonal in shape. Other Significant Diagnostic Features A. Secretory Structures - Secretions within wood may be intracellular or extracellular; that is, secretions may remain in producing cells, or be secreted from them. Gums and resins may be produced in intercellular spaces and are extra-cellular in nature being secreted from the producing cells. Lattices and oils, on the other hand, are generally produced within cells and are intercellular in nature. I. Intercellular Secretory Spaces (1) Intercellular cavities - sacs or pouches surrounded by a secretory epithelium consist of two types: (a) gum cavity; & (b) resin cavity (2) Intercellular canals - more or less elongated spaces, surrounded by a secretory epithelium, and being either axial or vertical, radial or horizontal in disposition. Canals may be normal or natural, or pathologic or traumatic. The latter is of more frequent occurrence and often results from break-down or degeneration of cells (termed as gummosis): (a) gum canal; and (b) resin canal II. Intracellular Secretory Structures 1. Laticifers - structures containing and producing latex (a) Articulated laticiferous tube - chains of cells in which the walls separating the cells remain intact, are perforated, or completely dissolved. These structures are often called latex vessels because of the resemblance to prosenchymatous vessels. (b) Non-articulated laticiferous tube - enlarged tubular cells ramifying througout the plant axis. Note: these are single cells, and are also called latex cells, except when they pass through a vascular ray when they are called latex tubes. 2. Secretory cells - this term is applied to cells of nearly normal size, or only somewhat enlarged, containing oil, resin, or mucilage Effects of Extractives to Wood Characteristics  Odor - the presence of extractives in some species of Family Meliaceae, such as Spanish Cedar and Kalantas, makes them emit resinous odorous that is sought after in the manufacture of tobacco boxes, pencils and similar products  Permeability - extractives block the intercellular spaces as well as the perforations in wood thus rendering some wood species less permeable or impermeable to water and other fluid chemicals. This is an important consideration in the manufacture of cooperage and in wood  preservation  Durability - extractives add strength to the wood by making it denser; being toxic to destructive organisms; and rendering the wood less permeable to moisture  Luster - presence of extractives makes wood less lustrous B. Tyloses - foam-like or sac-like deposits found in vessels. When viewed under the hand lens, tyloses appear as shiny obstructions partially or entirely blocking the pores. The woods of yakal, dao and molave have abundant tyloses. Tyloses are significant since they partially or often completely block the vessels in which they occur, a situation that can be either detrimental or beneficial depending upon the use to which the wood is put. White oak (Quercus spp.) heartwood, with its tightly plugged vessels, is widely used in making whiskey barrels, while open-vesseled red oak is avoided for this use because they lack tyloses. Difficulty or ease in seasoning and preservation activities are also affected by the presence of tyloses. How are tyloses formed and deposited in hardwood pores? C. Crystals - usually examined in longitudinal sections and valuable in wood identification. Frequently, crystals are found in axial parenchyma and ray cells and less frequently in septate fibers and in tyloses. In some specimens, there are modifications of the crystal-containing cells which are sufficiently consistent and infrequent to form useful guides to families and sometimes to genera. These are: (a) presence of crystals in enlarged cells or idioblasts, (b) changes in the cell wall, causing the crystalliferous cells to become sclerosed, and (c) the presence of crystals in variable size and shape in one cell. Types of crystals: (1) Druse - spherical clusters, either attached to the cell wall or lying free in the cells (2) Raphides - bundles of long needle-shaped crystals, tending to fill the whole cell (3) Elongated and rod-like - elongated crystals about four times as long as broad, with pointed or square ends; rod-like crystals are similar but are only about twice as long as broad and usually have squared ends. (4) Acicular - needle-shaped crystals which are often small, free in the cells and do not fill them (5) Crystal sand - a term applied to a granular mass of very fine small crystals (6) Rhomboidal, square or diamond-shaped - these are the most common of all crystal types. They may occur singly, or as two or more per cell. D. Silica - Silica occurs in timbers in many forms - inclusions, aggregates, concretions, corpuscles, bodies, etc. Silica inclusions refer to the more common occurrence of silica in which the granules are smaller than the lumina of the cells in which they occur, and have a  wrinkled or uneven surface. Vitreous silica refers to silica which is deposited as a lining on cell walls or completely fills the lumen of the containing cell. The presence of silica in wood has deleterious effect to most wood-working tools by making the blades dull after repeated use. That is why most sawmills working on coco- lumber have to retip their tools with stellite or carbide tips in order overcome the deleterious effect of silica on ordinary tools. Minute Structures of Wood (1) Prosenchyma - cells whose functions are mainly conductive and mechanical; with bordered pits (2) Parenchyma - tissue consisting of short, relatively thin-walled cells, generally with simple pits; concerned primarily with storage and distribution of carbohydrate (plant food). (3) Vessel element - one of the cellular components of a vessel (4) Vessel - articulated, tube-like structures of indeterminate length in porous woods; formed through fusion of cells in a longitudinal row and perforation of common walls in one of a number of ways (5) Tracheids - fibrous, lignified cells with bordered pits and imperforate ends; in conifers, the tracheids are very long and are equipped with large, prominent bordered pits on their radial walls; hardwood tracheids are shorter fibrous cells which are as long as the vessel elements they are associated with and usually possess small bordered pits. (a) vasicentric tracheids - short, irregularly-shaped fibrous cells with conspicuous bordered pits; abound in the proximity of the large earlywood vessels of certain ring-porous hardwoods; They are not arranged in definite longitudinal rows unlike vascular tracheids (b) vascular tracheids - specialized cells in certain hardwoods, similar in shape, size and arrangement to the small vessel elements but differing from them in having imperforate ends (c) ray tracheids - cells with bordered pits and devoid of living contents; found in woods rays of most softwood (d) resinous tracheids - contains amorphous deposits of reddish-brown or black resinous materials (e) strand tracheids - coniferous elements that arise from the further division of a cell which otherwise would have developed into the longitudinal tracheid which are usually longer (6) Fiber - elongated cell with pointed ends and a thick wall. (a) fiber tracheid - a fiber-like cell with pointed ends and bordered pits having lenticular to slit- like apertures; this term is generally applied to the fibers with bordered pits in angiosperms but is also applicable to the latewood tracheids of gymnosperms (b) libriform fibers - elongated, thick-walled cells with simple pits; usually longer than the cambial fusiform initials found in wood angiosperms. (7) Axial parenchyma - known as longitudinal parenchyma, derived from fusiform cambial initials.  fusiform cambial initials - cambial initials that, through repeated division, give rise to radially-oriented row of longitudinal elements of xylem and phloem  cambial initials - individual cells in the cambium layer. (a) axial strand parenchyma - cells of axial parenchyma arranged in a row along the grain which are formed through further (postcambial) division of a fusiform initial in the cambium (b) fusiform parenchyma cells - arise from a longitudinal cambial initial without subdivisions. i.e., it has the shape of a shorter fiber. (8) epithelial cells - excreting cells surrounding the cavity of resin and gum canals (9) ray parenchyma - parenchyma cells included in the wood rays, in contrast to longitudinal parenchyma which extends along the grain. (a) procumbent ray cells - narrow cells, elongated in the direction of the ray, of the type that composes homocellular rays and the body of heterocellular rays (b) upright ray cells - short, high cells (at least twice the height of an ordinary ray cells) on the margins of wood rays  homocellular ray - consisting entirely of one kind of ray cell.  heterocellular ray cells - in hardwood species, rays consisting of two kinds of cells, procumbent and upright cells; in conifers, a ray consisting of ray parenchyma and ray tracheids. Woody Plant Cell The cavities of the cells are called “cell lumen” and the separating walls between each cell are called “middle lamella”. The outer part of the cells, known as cell wall, is reportedly composed primarily of holocellulose and lignin. 1. Primary components a. Total polysaccharide fraction, expressed as holocellulose- 60-70% a.1. Cellulose- 40 to 50 percent - the main component of cell walls in most plants - the most important raw material of botanical origin available to man - the basic repeating element of cellulose is the cellobiose Figure 4. https://www.routledgehandbooks.com/doi/10.1201/b12487-5 a.2. Hemicellulose- 20 to 35 percent - Polysaccharides more or less ordered than the cellulose; common component of the cell matrix; has tremendous influence on certain physical properties of wood but secondary in importance to cellulose.  b. Lignin- 15 to 35%. The cementing substance of the wood/impart rigidity to the cell wall; name derived from lignin from lignum, the Latin name for wood; the basic structural unit is Phenyl-propane. 2. Secondary components (20-25%) a. Extraneous material or extractives- includes tannins, volatile oils and resins, gums, latex, alkaloids, and other complex organic compound; important in wood identification by providing distinguishable characteristics to species such as odor, color and taste; toxic or inhibitory to fungal and insect attacks. b. Ash- usually less than 1 percent; includes silica (causes dulling of machine tools) References Abasolo, W.P. Undated. Wood Structure and Identification: Handout Prepared for the Forester’s Licensure Examination Review Class sponsored by the FRM Department, UPLB, Collee, Laguna, Pp.12. Georgia Tech Biological Sciences. November, 2016. Organismal Biology: Plant Development I- Tissue differentiation and function. Retrieved from https://organismalbio.biosci.gatech.edu/growth-and-reproduction/plant-development-i- tissue-differentiation-and-function/. OpenStax College, Biology. October 17, 2013. Provided by: OpenStax CNX. Retrieved from http://cnx.org/content/m44700/latest/?collection=col11448/latest. BiologyOnline. January 26, 2021. Plant Tissues. Retrieved from https://www.biologyonline.com/tutorials/plant-tissues. National Alliance of Forest Owners. January, 2022. A Renewable Resource. Retrieved from https://nafoalliance.org/issues/a-renewable-resource/. Chemical Composition of Wood Information lifted from lecture of Dr. Ramon A. Razal, former Dean of CFNR-UPLB, in FPSS 127 on Properties and Utilization of Forest Products, CFNR-UPLB 2005.  Elemental Composition of Wood Element % Dry Weight Carbon 49 Hydrogen 6 Oxygen 44 Nitrogen Slight amounts Ash 0.1 Elemental Composition of Wood As an organic material, wood’s principal element is Carbon. Hydrogen and Oxygen, and to some extent, nitrogen are contained in organic compounds, hence they also make up wood. Ash includes elements such as calcium, potassium, magnesium, manganese and silicon. They constitute the non-combustible material that remains after wood is burned at high temperature in the presence of abundant oxygen. Elemental Composition of Wood – Nitrogen is present in amino acids and protein, particularly the enzymes that catalyze the various metabolic reactions in living parts of the wood and bark, in nucleic acids (these make up DNA and RNA), and in alkaloids in some plants. The major organic chemical constituents that make up the cell walls of wood are cellulose, hemicellulose and lignin. Exudents Galactomannose, etc. Glucose  Major Chemical constituents of a woody plant cell wall: Chemical Constituent Hardwood Softwood (% Dry weight)  Cellulose 40-44 40-44  Hemicellulose 15-35 20-32  Lignin 18-35 25-35 Taken together, cellulose and hemicellulose are referred to as HOLOCELLULOSE. They compromise the fraction of the woody plant cell wall. CHEMICAL COMPONENTS OF THE CELL WALL I. Primary Components Holocellulose the polysaccharide fraction of the woody element comprising about 60-70% Cellulose (40 -50%) long chain of glucose units that polymerize into microfibrils. Man can digest starch (a polysaccharide) but not cellulose which animals can digest because of cellulose enzymes present in their guts or stomach. Cotton is the purest form of cellulose known in nature. Hemicellulose (20-35%) matrix substance of the cell wall composed of two types of sugar molecules: xylans and glucomannans. Lignin (15-35%) made of intractable material which acts as the cementing substance of wood II. Secondary Components of Wood Tannins Volatile oils Resins Gums, latex, dyes, andother organic substance Ash – approximately0.5 to 1% of the wood substance (inorganic extraneous materials)  Review of Carbohydrates The simplest definition of Carbohydrates is that they are polyhydroxy aldehydes or ketones or compound derived from them. Their molecular weight range from less than 100 to well over 1 million. Many of low molecular weight carbohydrates have a sweet taste; this explains why they often called sugar.  Classes of Carbohydrates 1. Monosaccharides – These are also called simple sugar. – They can no longer be broken down to smaller sugar. – Examples are glucose, mannose, galactose, xylose and arabinose, which are the most common constituents of cell wall polysaccharides. – They are small compounds with 3 to 9 carbon atoms. – Glucose, mannose and galactose are hexose (containing 6 C atoms), while xylose and arabinose are pentoses (containing 5 C atoms).  Classes of Carbohydrates 2. Oligosaccharides – Consist of up to 9 monosaccharide units. – Oligosaccharides are further classified according to the number of monosaccharide units that they contain. Among them are: a) Disaccharides b) Trisaccharides c) Tetrasaccharides, and other sugars  Classes of Carbohydrates Types of Oligosaccharides a) Disaccharides – They consist of two monosaccharides linked by a single glycosidic bond; Example is cellobiose b) Trisaccharides – They consist of three monosaccharides linked by two glycosidic bonds. c) Tetrasaccharides, pentasaccharides and other sugars that contain less than 10 sugar units.  Classes of Carbohydrates 3. Polysaccharides – These are complex polymers composed of a large number of monosaccharide units joined together by several glycosidic linkages. – It can be further classified into: Homopolysaccharides- Only one kind of monosaccharide makes up the polymer. Heteropolysaccharides- At least two different kinds of monosaccharide make up the polymer.  CELLULOSE The aggregation of cellulose chains results in two distinct regions: Crystalline region- almost every hydroxyl group is involved in hydrogen bonding with its neighbors. Amorphous region- highly disorganized region. Hydroxyl groups are not hydrogen-bonded with hydroxyl groups of adjacent cellulose chains.  CELLULOSE It is regarded as the world’s most abundant naturally occurring polymer. It is built from several thousand glucose units that are linked end-to-end to form a long chain polymer. The repeating unit is CELLOBIOSE, giving a chain where every glucose residue is displaced 180 degrees with respect to its neighbors. Man has enzymes (e.g. amylase) in his digestive system that can break down starch but not cellulose. On the other hand, ruminants like cows, carabaos, and goats carry microorganisms in their stomach which secrete cellulase, an enzyme that is capable of breaking down cellulose to the more metabolically useful form, glucose.  HEMICELLULOSE Hemicelluloses are polysaccharides with much lower molecular weight than cellulose and serve as “matrix” material in the woody plant cell wall. The differences between cellulose and hemicellulose are: – Cellulose is a homopolysaccharide while hemicelluloses are heteropolysaccharides. – Cellulose has a much higher molecular weight than hemicellulose. The degree of polymerization (DP) of cellulose can reach up to 10,000; among hemicelluloses, the highest is only up to 200. – Cellulose is a linear molecule while hemicelluloses are usually branched. – Cellulose is less reactive and has much lower solubility in most solvents than hemicelluloses.  The principal types of hemicelluloses present in softwoods vary from those that are found in hardwoods. – Softwood hemicelluloses- Galactoglucomannan, Arabinoglucorunoxylan and Arabinogalactan. – Hardwood hemicelluloses- Glucorunoxylan, and Glucomannan.  Importance of Hemicellulose Important in pulp and paper making because their presence increases the rate at which fiber swelling and fibrillation occur. This reduces the time and power required for the beating operation, an important step for preparing pulp prior to sheet formation Help improve the bonding between fibers in the finished paper.  LIGNIN Second only to cellulose as the most abundant naturally occurring polymer. It is found in terrestrial, vascular plants, in all kinds of tissues besides wood and bark, as in leaves, sugar cane, corncobs, coconut husks, peanut shells, etc. Molecular Formula of lignin: C9H10O2, C10H12O3, C11H14O4  LIGNIN In the cell wall, the middle lamella and the primary wall consist mainly of lignin, where it serves as a cementing substance that binds wood cells together. Lignin imparts stiffness and rigidity to the cell wall, and increases the toxicity of wood to microbiological agents of decay. Like cellulose and hemicelluloses, lignin is a polymer. Lignin is very difficult to isolate from a plant tissue No extraction method has yet been developed that does not alter the “native” structure of lignin.  LIGNIN Lignin preparation are therefore classified according to the method used, as follows: – Klason lignin- lignin is isolated by reacting wood (in flour form) with 72% sulfuric acid. – Cellulytic enzyme lignin- Enzymes are used to remove polysaccharides from wood. – Dioxane lignin- Wood flour is extracted with dioxane containing water and HCl. – Biorkman or milled wood lignin- Considered as the best lignin preparation. Wood is ground in a ball mill in the presence of a solvent. e.g. toluene, followed by extraction with dioxane-water. – Sulfate or kraft lignin- Obtained from the craft pulping process, where wood chips are treated with a mixture of sodium hydroxide and sodium sulfide.  Cell Wall Composition Lignin is the dominant organic compound between cells, but its concentration decreases towards the cell lumen. Both the middle lamella and primary wall are very thin and so the greatest volume of lignin would be located in the thicker secondary wall particularly the S-2 layer. Cellulose and hemicelluloses comprise the bulk of the secondary wall, which is made up of the S-1, S-2 and the S-3 layer. The S-2 layer is the thickest layer, where cellulose chains are deposited in thin layers with only a very slight angle relative to the cell’s longitudinal axis. Because of its bulk, the S-2 layer dictates most of the physicochemical and mechanical properties of wood, particularly in relation to dimensional changes that accompany moisture loss or adsorption.  EXTRACTIVES Chemical components that are extraneous to the cell wall, which can be extracted with neutral solvent. They are mostly deposited within the cell cavities of lumen, although it is conceivable that low molecular weight extractives are able to penetrate cell walls. Extractive content usually does not exceed more than 10% of the dry weight of the wood. Color and natural durability are perhaps two of the most important properties that extractives impart to wood. Extractives are found mainly in the heartwood in all species. The largest amounts are found in the portion of the heartwood adjacent to the sapwood. The concentration of extractives decreases gradually towards the pith.  Major Classes of Extractives Terpernoids and steroids – Found in resin canals and helps in protecting wood against microbiological damage or insect attack. – These derived from isoprene units and are sometimes referred to as isoprenoids. Fats and waxes – These constitute a supply of reserve food and are located mainly in parenchyma cells. Phenolics – This group of extractives is located largely in the heartwood and in the bark. – They have fungicidal properties and protect the tree against microbiological attack. – The variety of phenolics found in plant is used as a basis for the taxonomy and identification of species in certain plant families. – The different groups of phenolics are:  Major Classes of Extractives Different Groups of Phenolics: – Stillbenes; example is pinosylvin, present in pines. – Lignans; example is pinoresinol; also in pines – Hydrolyzable tannins – Flavanoids; example is epicatechin – Proanthocyanidins or condensed tannins; They could be found in the wood and bark of many species, like those of the leguminous species. The barks of Philippine mangrove species are rich in tannins. An important industrial use is in converting animal hide into leather. – Quinones; Most vegetative dyes fall under this group. An example is tectoquinone in teak, which partly explains the natural durability of this species.  PROXIMATE CHEMICAL COMPOSITION AND UTILIZATION OF WOOD The chemical properties of the Philippine woods are usually reported as the result of the proximate chemical analysis. Values are expressed as a percentage of the oven-dry weight of wood. The following consists of the tests done and what they could mean as far as utilization of wood is concerned: 1. Ash content; This represents all the non-combustible portion that remains after burning wood in a furnace at a very high temperature. A high ash content usually suggests high silica content, which makes some species very difficult to cut because they tend to dull tools very rapidly.  PROXIMATE CHEMICAL COMPOSITION AND UTILIZATION OF WOOD 2) Holocellulose – This represents the total carbohydrate materials in wood. – A high holocellulose content is desirable in the pulp and paper industry because it is correlated with high pulp yield. 3) Lignin – This is usually determined by the Klason method. – A species with high lignin content is not suitable for pulp and papermaking. – Among the problems associated with high lignin content is low pulp strength, more pulping and bleaching chemical requirements, fast yellowing or browning of paper or a combination of these. 4) Pentosans – These are part of the non-cellulosic carbohydrates and chiefly refer to the xylan and araban fractions.  PROXIMATE CHEMICAL COMPOSITION AND UTILIZATION OF WOOD Solubilities in: a) Alcohol: Benzene Those that are soluble in alcohol:benzene include fats, waxes, “resins” and other organic-soluble materials. High alcohol:benzene solubility means high extractive content, suggesting that the wood may be durable. However, it could also mean utilization problems such as pith and high chemical consumption in pulp and paper making, non-treatability with wood preservatives, difficulty in finishing, gluing and in bond  Solubilities of Wood Components b) Hot water- this extract includes organic salts, gums, pectin-like material and some water- soluble phenolic constituent. c) 1% NaOh or caustic soda solubility – Wood solubility in 1% NaOH solution reflects the degree of fungal decay in wood. – As wood decays, the percentage of alkali-soluble material increases in proportion to the reduction in pulp yield.  FPU 192 Chemistry of Forest Products Chapter Celluloses: Formation, Structure, Reactions and Derivatives 3A Objectives: To understand and explain the chemical processes occurring in the cellulosic part of the wood. Wood Composition Cellulose a polysaccharide (C6H12O6)x of glucose units that constitutes the chief part of the cell walls of plants, occurs naturally in such fibrous products as cotton and kapok, and is the raw material of many manufactured goods such as paper, rayon, and cellophane. (Merriam Webster) Many properties of cellulose depend upon the degree of polymerization or chain length and the number of glucose molecules constituting the polymer molecule. Cellulose is odorless and insoluble in water and most organic solvents. It is biodegradable and chiral. At high temperatures, it can be broken down into glucose by treating it with concentrated mineral acids. It is more crystalline when compared to starch. But starch goes from crystalline to amorphous transition at 60-70 degrees but cellulose, on the other hand, requires 320 degrees and a pressure of 25 megapascals. Introduction Cellulose is the most abundant biopolymer available in nature since it is one of the major components of the cell walls of most of the plants. It is a homopolymer of anhydroglucose, with the glucose residues linked in a ß-1,4 fashion. Cell walls of plant cells attribute their mechanical strength to cellulose. Cellulose owes its structural properties to the fact that it can retain a semi- crystalline state of aggregation even in an aqueous environment, which is unusual for a polysaccharide. As far as cellulose-based products are concerned, paperboard and paper are the most commonly used ones. Smaller amounts of cellulose when processed under appropriate conditions, can be converted to a wide variety of derivatives, which can be used in the manufacture of a few commercial products like cellophane and rayon. Since cellulose is a homopolymer of a glucose derivative, it is a great source of fermentable sugar. It is cultivated in the form of energy crops for the production of ethanol, ethers, acetic acid, etc. Besides energy requirements the industrial demands of cellulose are fulfilled by wood pulp and cotton crops. Cellulose also fulfils the dietary requirements of some animals, particularly ruminants and termite, they can digest cellulose with help of symbiotic microorganisms present in their gut, while some organisms secrete a group of enzymes called cellulases to aid the degradation of cellulose molecules. Human beings are unable to digest cellulose due to lack of cellulases, thus cellulose acts as a hydrophilic bulking agent for faeces and potentially aids in defecation. 1. Expound on cellulases? What specific microorganisms possess this kind of enzymes? (5 points). Answer: Overview Among the various raw materials that nature has placed at our disposal for industrial purposes, cellulose has from time immemorial occupied a prominent position. Its abundance is attributed to the constant photosynthetic cycles taking place in higher plants, which can synthesize around 1011 ± 1012 tons of cellulose in a rather pure form. Since time immemorial it has served mankind either as a construction material or as a versatile starting material for chemical reactions for the production of artificial cellulose-based threads and biofilms as well as for the production of a variety of stable cellulose derivatives which are used for various industrial and domestic applications. Cellulose was used for various biochemical conversions even before its polymeric nature was recognized and well-understood. In the process of recognizing and understanding its polymeric structure, it led to the discovery of nitrocellulose, the synthesis of organo-soluble cellulose acetate, and the preparation of Schweizer’s reagent (first cellulose solvent). Another area of great interest was nanocellulose, the nanostructure of cellulose has proven to be advantageous because of its applications in a variety of fields. Due to such great economic significance of tree cellulose, the current scientific focus is more towards cellulose biosynthesis as it is still not well understood. Most of the recent findings concerning the molecular mechanism of cellulose biosynthesis in higher plants resulted from research in model herbaceous plants and fibre crops and have been reviewed recently. All these aspects trigger a researchers’ curiosity and makes them want to dig deeper and unveil other properties and applications of cellulose. Formation and Location of Cellulose in the Cell Wall Plant cell walls are dynamic structures that define the shape and size of a plant cell, provide structural Difference between Alpha support to the plant body, protect cells from pathogens Glucose and Beta Glucose and serve as nodes of communication between the The α-glucose and β-glucose symplast and apoplast. Plant cell walls are composed are the two isomers of the of several groups of polysaccharides including glucose. Both isomers are cellulose, hemicelluloses, and pectins, as well as structurally very much similar structural proteins and phenolic compounds s (Ivakov but exhibit quite different and Persson, 2012; Lampugnani et al., 2018 as cited properties at different stages. by Kieber, 2019). Glucose is the most familiar name in the house. It tastes Cellulose, which consists of chains of b-1,4-linked sweet and we often consider glucose units, is synthesized at the plasma membrane it as an energy-giving (PM) and organized into microfibrils, which are the substance also. Glucose is main load bearing elements of cell walls. Cellulose is actually a sugar which has two synthesized by the enzyme cellulose synthase, and in isomers namely, α-glucose all cases this enzyme is predicted to be a membrane and the β-glucose. These both protein that utilizes UDP-glucose as the sugar donor in isomers have their own a direct transfer reaction 9. The glucan chain is property. elongated from the non-reducing end 20 processively and although suggestions for the requirement of a Sugars come under the primer by cellulose synthase have been made 11, no category of carbohydrates. primer has yet been identified (Sexena et. al., 2001). There are many kinds of sugars as per the structure of The plant cell wall is made up in part of cellulose the sugar. It can be molecules arranged to form microfibrils. Numerous monosaccharide, disaccharide microfibrils that are combined is needed to form a and polysaccharides. If we cellulose fiber. Microfibrils are 5 to 12 mm wide and look at the monosaccharides, every fiber [microfibril] contains 20 to 40 individual they contain just one chains. molecule. Dextrose or Glucose is a well-known monosaccharide, fructose and 2. What is a microfibril? Where is microfibril located? galactose are the other (3 points) examples of monosaccharide. Disaccharides are the complex Answer: structure of sugars, Sucrose and maltose come as the examples of disaccharides. Structure of Cellulose The chemical structure of cellulose consists of linear chains of glucose units linked by β-1,4-glycosidic bonds. Glucan chains of cellulose aggregate via hydrogen bonds and van der Waals forces to form a long thread-like crystalline structure called a cellulose microfibril (Harris et al., 2010 as cited by Rongpipi et. al., 2019). The molecular structure is responsible for its significant properties: Chirality, hydrophilicity, degradability and chemical variability due to high reactivity from the donor group—OH. The superior hydrogen bonds add crystalline fibre structures to cellulose. Figure 1 presents the four Figure 1. Major pathways of formation of cellulose. Image by: Praveen et. al. different pathways which determine the major processing routes. The most famous and highly used pathway is the manufacture of cellulose from plants. It is established that cellulose is found in its purest form from the seed hairs of cotton. The wood cellulose, on the other hand forms a composite with lignin and other polysaccharides, which is further separated by large scale chemical pulping and purification processes. Cellulose is a made up of thousands of D-glucose subunits. The glucose subunits in cellulose are linked via beta 1-4 glycosidic bonds. Contrary to the other polysaccharides, the orientation of glucose molecules in cellulose is reversed. They have beta orientation in which the hydroxyl group of the anomeric carbon or carbon number one is directed above the plane of the glucose ring. The hydroxyl groups of the rest of the carbon atoms are directed below the plane of the ring. In order to make beta 1-4 glycosidic bonds, every alternate glucose molecule in cellulose is inverted. The hydroxyl group of carbon 1 is directed upwards, and that of carbon 4 is directed downward. Now, to make a beta 1-4 glycosidic bond, one of these molecules should be inverted so that both the hydroxyl groups come in the same plane. This is the reason for the inversion of every alternate glucose molecule in cellulose. Cellulose is an unbranched molecule. The polymeric chains of glucose are arranged in a linear pattern. Unlike starch or glycogen, these chains do not undergo any coiling, helix formation or branching. Rather, these chains are arranged parallel to each other. The hydrogen bonds are formed between these chains due to hydrogen atoms and hydroxyl groups which firmly hold the chains together. This results in the formation of cellulose microfibrils that are firm and strong. Reactions of Cellulose: Cellulolysis Cellulolysis is essentially the hydrolysis of cellulose. In the low and high pH conditions, hydrolysis is a reaction that takes place with water, with the acid or base providing H+ or OH- to precipitate the reaction. Hydrolysis will break the β-1,4-glucosidic bonds, with water and enzymes to catalyze the reaction. Types of intermediate units that are made from cellulose: The main monomer that composes cellulose is glucose. When two glucose molecules are connected, it is known as cellobiose – one example of a cellobiose is maltose. When three glucose units are connected, it is called cellotriose – one example is β -D pyranose form. And four glucose units connected are called cellotetraose. Each of these is shown below in the figure: Figure 2. Cellobiose, or maltose (glucose + glucose) chemical structure. Figure 3. Cellotriose in the β-D-pyranose form. Figure 4. Cellotetraose. Reaction types that are catalyzed by cellulose enzymes: 1. Breaking of the noncovalent interactions present in the structure of the cellulose, breaking down the crystallinity in the cellulose to an amorphous strand. These types of enzymes are called endocellulases. 2. The next step is hydrolysis of the chain ends to break the polymer into smaller sugars. These types of enzymes are called exocellulases, and the products are typically cellobiose and cellotetraose. 3. Finally, the disaccharides and tetrasaccharides (cellobiose and cellotetraose) are hydrolyzed to form glucose, which are known as β-glucosidases. Two types of cellulase systems: A noncomplexed cellulase system is the aerobic degradation of cellulose (in oxygen). It is a mixture of extracellular cooperative enzymes. A complexed cellulase system is an anaerobic degradation (without oxygen) using a “cellulosome.” The enzyme is a multiprotein complex anchored on the surface of the bacterium by non-catalytic proteins that serve to function like the individual noncomplexed cellulases but is in one unit. Cellulose Derivatives (Read more on the attached Scientific Paper in your GCR) Definition of terms: Acetylation - In chemistry, acylation is a broad class of chemical reactions in which an acyl group (R−C=O) is added to a substrate. The compound providing the acyl group is called the acylating agent. Acyl - acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an alkyl group (R−C=O). Acetate- a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic or radical base) Butyric acid - from Ancient Greek: βούτῡρον, meaning "butter"), also known under the systematic name butanoic acid, is a straight-chain alkyl carboxylic acid with the chemical formula CH3CH2CH2CO2H. It is an oily, colorless liquid with an unpleasant odor. Isobutyric acid (2-methylpropanoic acid) is an isomer. Salts and esters of butyric acid are known as butyrates or butanoates. The acid does not occur widely in nature, but its esters are widespread. It is a common industrial chemical and an important component in the mammalian gut. MONOMERS AND POLYMERS IN CHEMISTRY Monomers The word monomer comes from mono- (one) and -mer (part). Monomers are small molecules which may be joined together in a repeating fashion to form more complex molecules called polymers. Monomers form polymers by forming chemical bonds or binding supramolecularly through a process called polymerization. Sometimes polymers are made from bound groups of monomer subunits (up to a few dozen monomers) called oligomers. To qualify as an oligomer, the properties of the molecule need to change significantly if one or a few subunits are added or removed. Examples of oligomers include collagen and liquid paraffin. A related term is "monomeric protein," which is a protein that bonds to make a multiprotein complex. Monomers are not just building blocks of polymers, but are important molecules in their own right, which do not necessarily form polymers unless the conditions are right. Examples of Monomers Examples of monomers include vinyl chloride (which polymerizes into polyvinyl chloride or PVC), glucose (which polymerizes into starch, cellulose, laminarin, And the third variety known as and glucans), and amino acids (which polymerize into polysaccharides has the peptides, polypeptides, and proteins). Glucose is the example of starches and most abundant natural monomer, which polymerizes cellulose. by forming glycosidic bonds. Polymers The glucose has two isomers, The word polymer comes from poly- (many) and - alpha glucose and beta mer (part). A polymer may be a natural or synthetic glucose. The main difference between the two lies in the macromolecule comprised of repeating units of a orientation of the (-OH) smaller molecule (monomers). While many people use hydroxyl group. In both cases, the term 'polymer' and 'plastic' interchangeably, the hydroxyl group gets polymers are a much larger class of molecules which connected to the first carbon includes plastics, plus many other materials, such as atom, just the geometry is cellulose, amber, and natural rubber. different. In the structure of Lower molecular weight compounds may be Alpha glucose, the orientation distinguished by the number of monomeric subunits is (1-hydroxyl) and (4- they contain. The terms dimer, trimer, tetramer, hydroxyl). These both get pentamer, hexamer, heptamer, octamer, nonamer, connected at the same side of decamer, dodecamer, eicosamer reflects molecules the carbon atom. In case of containing 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 20 Beta glucose, the orientation monomer units. is again the (1-hydroxyl) and (4-hydroxyl) , but this time, Examples of Polymers these both get connected with the carbon atom at the Examples of polymers include plastics such as opposite sides of each other. polyethylene, silicones such as silly putty, biopolymers So, both the glucose, alpha such as cellulose and DNA, natural polymers such as glucose and beta glucose have rubber and shellac, and many other important the same structure, just the macromolecules. orientation of the hydroxyl Groups of Monomers and Polymers group is different. The classes of biological molecules may be grouped into the types of polymers they form and the monomers that act as subunits: Lipids - polymers called diglycerides, triglycerides; monomers are glycerol and fatty acids Proteins - polymers are known as polypeptides; monomers are amino acids  Nucleic Acids - polymers are DNA and RNA; monomers are nucleotides, which are in turn consist of a nitrogenous base, pentose sugar, and phosphate group Carbohydrates - polymers are polysaccharides and disaccharides*; monomers are monosaccharides (simple sugars) *Technically, diglycerides, and triglycerides are not true polymers because they form via dehydration synthesis of smaller molecules, not from the end-to-end linkage of monomers that characterizes true polymerization. 3. Explain how polymers are form? (5 points) Answer: References: Akinosho, H., Yee, K., Close, D., & Ragauskas, A. (2014). The emergence of Clostridium thermocellum as a high utility candidate for consolidated bioprocessing applications. Frontiers in Chemistry, 2. DOI:10.3389/fchem.2014.00066. Retrieved on January 27, 2023. A Level Biology. Cellulose. Retrieved from: https://alevelbiology.co.uk/notes/cellulose/#0- introduction. Retrieved on January 27, 2023. BJYU’S. 2023. Cellulose. Retrieved from: https://byjus.com/chemistry/cellulose/. Retrieved on January 29, 2023. BJYU’S. 2023. Polysaccharides. Retrieved from: https://byjus.com/biology/polysaccharides/#:~:text=What%20are%20Polysaccharides%3F,comp onent%20of%20a%20plant%20cell. Retrieved on January 29, 2023. Gupta, P.V., Raghunath, S.S., Prasanna, D.V., Venkat, P., Shree, V., Chitchananthan, C., Choudhary, S., Surender, K., and Geetha, K. An Update on Overview of Cellulose, Its Structure and Applications. DOI: http://dx.doi.org/10.5772/intechopen.84727. Retrieved on January 28, 2023. Kieber, J. J., & Polko, J. (2019). The Regulation of Cellulose Biosynthesis in Plants. The Plant Cell, tpc.00760.2018. doi:10.1105/tpc.18.00760. LibreTexts (2021). The Reaction of Cellulose- Cellulolysis. Retrieved from: https://eng.libretexts.org/Bookshelves/Biological_Engineering/Alternative_Fuels_from_Biomass _Sources_(Toraman)/06%3A_General_Ethanol_Production/6.03%3A_Enzymatic_Biochemistry _and_Processing/6.3a%3A_The_Reaction_of_Cellulose-_Cellulolysis. Retrieved on January 27, 2023. Li, S., Bashline, L., Lei, L., & Gu, Y. (2014). Cellulose Synthesis and Its Regulation. The Arabidopsis Book, 12, e0169. doi:10.1199/tab.0169. Retrieved on January 28, 2023. Rongpipi, S., Ye, D., Gomez, E. D., & Gomez, E. W. (2019). Progress and Opportunities in the Characterization of Cellulose – An Important Regulator of Cell Wall Growth and Mechanics. Frontiers in Plant Science, 9. doi:10.3389/fpls.2018.01894. Retrieved on January 30, 2023. Saxena, I. M., & Brown, R. M. (2001). Biosynthesis of Cellulose. Molecular Breeding of Woody Plants, Proceedings of the International Wood Biotechnology Symposium (IWBS), 69–76. DOI: 10.1016/s0921-0423(01)80057-5. Retrieved on January 28, 2023. Shen, D. K., & Gu, S. (2009). The mechanism for thermal decomposition of cellulose and its main products. Bioresource Technology, 100(24), 6496 6504. DOI:10.1016/j.biortech.2009.06.095. Retrieved February 1, 2023. ThoughtCo. 2023. Monomers and Polymers in Chemistry. Retrieved from: https://www.thoughtco.com/monomers-and-polymers-intro-608928. Retrieved on January 29, 2023. Unacademy. 2023. Difference between Alpha Glucose and Beta Glucose. Retrieved from: https://unacademy.com/content/neet-ug/difference-between/alpha-glucose-and-beta- glucose/#:~:text=The%20glucose%20has%20two%20isomers,just%20the%20geometry%20is% 20different. Retrieved on January 29, 2023. 1 FPU 192 Chemistry of Forest Products Chapter Alpha(α) and Beta(β) Glucose: Comparison, Structures, Explanation 3A.1 Glucose, also known as dextrose is the most common simple sugar (monosaccharide). It has two isomeric structures, i.e. dextrose-(D) glucose and Lactose-(L) glucose. The dextrose-(D) glucose contains two further isomers, i.e. alpha (α) and beta (β) glucose. The key difference between alpha (α) and beta (β) glucose is the orientation of hydroxyl (-OH) group attached to the first carbon atom. The two dimensional graphical representation of these isomeric glucose structures shows that the α-glucose has (1-hydroxyl) and (4-hydroxyl) orientations on the same side. On the other hand, β-glucose has the orientations of (1-hydroxyl) and (4-hydroxyl) on opposite sides. By relative stability, alpha and beta glucoses exist naturally as 36 : 64 respectively. Figure 1. Comparison of Alpha and Beta Glucose The above figure clearly depicts the geometrical orientation of hydroxyl groups on alpha (α) glucose and beta (β) glucose structures. Besides this main difference i.e. different orientation of hydroxyl group at first carbon atom, the rest of entire structures of alpha (α) glucose and beta (β) glucose are the same. 2 Difference between alpha(α) and beta(β) glucose Alpha Glucose Beta Glucose Alpha(α) glucose has hydroxyl groups of 1 and 4 Beta(β) glucose has hydroxyl groups of 1 and 4 positions on same sides positions on opposite sides Alpha(α) glucose is less stable due to the steric Beta(β) glucose is more stable due to opposite hinderance of OH groups, being on same sides sides of OH groups Alpha glucose is higher in energy than beta Beta glucose is lesser energetic glucose It has low melting point i.e. 146 °C It has higher melting point i.e. 150 °C It has a specific rotation of 112.2 degrees It has a specific rotation of 18.7 degrees Alpha glucose structure is easily broken down by Beta glucose structure is resistant against enzyme enzymes due to its high reactivity action due to its low reactivity The glycosidic bond between two alpha glucose The glycosidic bond between two beta glucose structures results in the formation of maltose structures results in the formation of cellobiose It can only be crystallized in the form of α- It can be crystallized in the form of β- glucopyranose glucopyranose or β-glucopyranose hydrate It has a specific rotation of 112.2 degrees It has a specific rotation of 18.7 degrees Alpha glucose structure is easily broken down by Beta glucose structure is resistant against enzyme enzymes due to its high reactivity action due to its low reactivity The glycosidic bond between two alpha glucose The glycosidic bond between two beta glucose structures results in the formation of maltose structures results in the formation of cellobiose It can only be crystallized in the form of α- It can be crystallized in the form of β- glucopyranose glucopyranose or β-glucopyranose hydrate Polymerization of alpha(α) glucose yields starch Polymerization of beta(β) glucose yields cellulose Food sources of alpha(α) glucose include whole Food sources of beta(β) glucose include fibrous grains, potatoes, beans and corn, and sucrose, etc foods like legumes, nuts, yeast, algae, and mushrooms, etc Similarities among alpha (α) and beta (β) glucose Both alpha(α) and beta(β) glucose structures are simple sugar monomers. They can be crystallized from their aqueous solutions, although, alpha(α) glucose cannot be crystallized as α-glucopyranose hydrate. They both have the same number of chiral carbon centers i.e. 4. Both alpha(α) and beta(β) glucose are optically active organic compounds. Alpha(α)-D Glucose 3 Alpha(α)-D glucose is an isomer of dextrose(D) glucose with the identification of having hydroxyl (-OH) groups on 1 and 4 positions on the same sides of the plane. It can also be referred to as an orientation in which the hydroxyl group of 1 position is on the opposite side to that of (-CH2OH). This isomer of glucose is less stable than the beta(β) glucose because of the steric hindrance of hydroxyl groups, being on the same sides. This makes the natural abundance of alpha glucose, 36%. The position of the hydroxyl group has a great influence on the properties of compounds for which, alpha glucose is generally more reactive than beta glucose. It has a melting point of 146 °C and a specific rotation of 112.2°. Moreover, it can be crystallized from its aqueous solution in the form of α-glucopyranose. The chair conformation of alpha dextrose glucose [α-D glucose] shows the same sides of hydroxyl groups of 1 and 4 positions, i.e. lower to the plane in the above diagram. Examples of Alpha(α) Glucose yields are: Maltose is made by the joining of two α-glucose molecules. Sucrose is made from one α-glucose and one fructose molecule. Lactose is made from one α-glucose and one galactose molecule. Beta(β)-D Glucose Beta(β) glucose is also an isomer of dextrose(D) glucose. It has the identification of having hydroxyl (-OH) groups of 1 and 4 positions on opposite sides. The position of the hydroxyl group of 1 position is on the same side as (-CH2OH). The beta glucose isomer is more stable than alpha glucose due to the reduced steric hindrance as the bulky groups are away from each other. This makes beta its natural abundance 64%. Beta(β) glucose has a melting point of 150 °C and a specific rotation of 18.7°. Beta glucose can be crystallized from the aqueous solutions as β-glucopyranose and β-glucopyranose hydrate. 4 The chair conformation of beta dextrose glucose [β-D glucose] shows the opposite sides of 1 and 4 positioned hydroxyl groups. Beta(β) Glucose is the monomer unit in cellulose fibers. These fibers are linear due to the beta acetal linkages in beta glucose. Acetal is another name for these glucose monomers under the condition that they are duly protonated. The D-glucose monomers can cyclize to form hemiacetal structures. Under acidic conditions, these hemiacetals can react with further alcoholic groups to form acetals. 5 What is beta glucose? Beta glucose is an isomer of dextrose(D) glucose having a hydroxyl group on 1 position, on the opposite side, as the hydroxyl group of position 4. An example of a polymer having beta glucose monomers is cellulose. It has a high melting point and more stability. What is alpha glucose? It is an isomer of D-glucose having a hydroxyl group located downward. It has a low melting point and high stability. Alpha glucose is an isomer of dextrose(D) glucose having a hydroxyl group on 1 position, on the same side, as the hydroxyl group of position 4. An example of a polymer having alpha glucose monomers is maltose. It has a lower melting point and less stability. What are the functions of alpha and beta glucose? Alpha and beta glucose are very important for living organisms. Alpha glucose is the building block of starch while beta glucose is the building block of cellulose. Amylopectin, lactose, maltose, and galactose, etc also contain alpha and beta glucose as their building blocks.  CHAPTER 3-B HEMICELLULOSE FPU 192 Chemistry of Forest Products Definition also known as polyose one of a number of heteropolymers alongside cellulose defined as cell wall polysaccharides that have the capacity to bind strongly to cellulose micro fibrils by hydrogen bonds (Roland et al., 1989) Degree of Polymerization (DP or Xn) degree of polymerization of glucose units in hemicelluloses is in the range of 100–200 units, which is much lower than cellulose  usual DP values in wood are reported to be between 300 and 1700  in nature, cellulose has a DP of approximately 10,000 glucopyranose units in wood cellulose and of 15,000 units in plant cellulose  Hemicellulose in Harwood and Softwood (Kumar et. al., 2021) Hemicellulose HARDWOOD SOFTWOOD  consists of pentose, that is,  consists of hexose subunits xylose, subunits such as glucose, mannose, and galactose Pentose - pentose is a Hexose - any of the class of monosaccharide with five simple sugars whose molecules carbon atoms. The chemical contain six carbon atoms, such formula of many pentoses is C as glucose and fructose. They ₅H ₁₀O ₅. generally have the chemical formula C6H12O6. Hemicellulose in Wood and Non-wood (Benaimeche et. al., 2020) Non-wood fibers Wood fibers  such as grasses  wood fibers are (wheat, corn, rice) composed of 25%– contain up to 40% of 35% of hemicellulose the major by dry weight hemicellulose found in grasses Hemicellulose Classification (Scheller et. al., 2010)  hemicellulose (polysaccharide) have e β- (1→4)-linked backbones with an equatorial configuration Hemicellulose in ALL Hemicellulose in POALES and TERRESTRIAL PLANTS (cell wall) other few groups (cell wall)  include xyloglucans,  includes xyloglucans, xylans, mannans and xylans, mannans and glucomannans glucomannans, and β-(1→3,1→4)-glucans  STRUCTURE AND DISTRIBUTION (Scheller et. al., 2010) I. Xyloglucan (XyG)  has been found in every land plant species that has been analyzed, including mosses EXCEPT in Charophytes  the most abundant hemicellulose in primary walls of spermatophytes except for grasses  STRUCTURE AND DISTRIBUTION (Scheller et. al., 2010) II. Xylans  a polysaccharide consisting mainly of xylose residues  they may constitute more than 30% of the dry weight in plants  mainly constituted by D-xylose as the monomeric unit, and traces of L-arabinose are also present  Xylans of several wood species, particularly of hardwoods, are acetylated  STRUCTURE AND DISTRIBUTION (Scheller et. al., 2010) III. Glucomannans  β-(1→4)-linked polysaccharides containin