Wood Components  - Wood is made up of three major or basic components:  1) cellulose, the framework or skeleton;  2) hemicellulose, the matrix;  3) lignin, the encrusting or "glue-like" substance that holds and binds the cells together and gives the cell wall rigidity.  Other components are extractives, which are organic compounds that are usually in the lumens of dead heartwood cells, and tannins, which are complex substances.  Cellulose is the most abundant organic chemical on earth.  The amount of cellulose in normal wood is about the same in softwoods and hardwoods, about 42%.  The specific gravity of cellulose is 1.53.  How densely the cellulose is packed, and how abundant other substances are, makes up the density or weight of wood.  Cellulose is made up of glucose units in a long line.  Cellulose is made up of highly ordered portions called crystalline and portions not highly ordered called amorphose.  Hemicelloses are polysaccharides associated with cellulose and lignin.  Pectin is also a polysaccharide, but it is a much larger molecule than the hemicelluloses.  The part you need to know is that the sugar units are the building blocks for these compounds, and the sugar units "lock up" their energy as these large molecules are formed.  Later, when the microorganisms attack wood, they begin cleving or breaking the large molecules into smaller and smaller units until they can get to the energy bonds.  Fungi can do it, and some protozoa, but not us.  Lignins are very complex three-dimensional polymers made up of phenylpropane units.  They encrust the intercellular space and any openings in the cell wall after the cellulose and hemicellulose has been deposited.  Wood is made up of 25 to 30% lignin.  In pulping, the lignin is removed.  Many microorganisms can not digest lignin.  Some can, and they may be very valuable for biological pulping.  Fomes pini digests lignin very effectively. 

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