Cellulose is by far the earth's most abundant biological polymer.  It is a major structural component of the plant cell wall or extracellular matrix.  Like amylose cellulose is a linear homopolymer of D-glucose units with carbon 1 of the non-reducing end linked to carbon 4 of the glucose on the reducing end.  However, for cellulose the glycosidic linkages are ß-1,4 rather than a-1,4 in the case of amylose.  This seemingly small difference has enormous effects on the structures of these two molecules.  Glucose units linked a-1,4 are slightly bent and such polymers tend to adopt helical or corkscrew conformations.  Cellulose with ß-1,4 glycosidic bonds can adopt a fully extended conformation with the more stable alternating 180° flips of the glucose units: 

Cellulose is one of the principal components of both primary and secondary plant cell walls being up to 40% of secondary cell walls.  The degree of polymerization of cellulose in primary walls is ~2,000-6,000 glucose units and ~10,000 residues in secondary walls.  These cellulose polymers are packed parallel to each other in structures known as microfibrils composed of ~36 cellulose chains.  In secondary walls these microfibrils are often further associated in bundles or macrofibrils.  See Fig. 1 of Delmer and Amor (1995) The Plant Cell 7, 987-1000:

This allows intra-chain, inter-chain and inter-sheet hydrogen bonding in the cellulose fibrils resulting in a structure of great strength:

Cellulose is synthesized in a multi-subunit complex in the plasma membrane with each unit of the complex responsible for polymerization, secretion, alignment and possibly crystallization of each cellulose chain of the microfibrils.  Sucrose synthase provides the glucose needed for cellulose synthesis in the form of UDP-glucose and cellulose synthase catalyzes the ß-1,4 glycosidic bond formation of the cellulose polymers.  This complex with ~36 units (for each cellulose polymer of a microfibril) is hypothesized to move in the plasma membranes and the pattern of movement is guided by microtubules that are adjacent or connected to the synthase complex. See Fig. 2 of Delmer and Amor (1995) The Plant Cell 7, 987-1000:

Most all plant cells have primary cell walls.  Plant tissues with only primary cell walls are rather soft and their rigidity is maintained by turgor pressure.  Wilting of such plant tissues can occur when they do not contain sufficient water to maintain turgor pressure.  Some terminally differentiated plant cells have extensive additional cell wall deposits inside the primary walls known as secondary walls that can be several times the thickness of the primary walls.  The secondary walls are often laid down in layers with the cellulose microfibrils having different but defined orientations (Fig. 5.3 of the Dey & Harborne 1997 text on reserve):

In addition to cellulose and lignin of secondary walls, plant cell walls contain an amorphous matrix composed of hemicelluloses, pectic substances, proteins and lipids (Fig. 5.2 of Dey & Harborne, 1997):

Hemicelluloses are a diverse group of carbohydrate polymers that vary among different plant groups and between primary and secondary walls.  Like cellulose, hemicelluloses are chains of sugar monomers mostly joined by ß-1,4 glycosidic linkages.  However unlike cellulose, the chain lengths are shorter (e.g. several hundred residues), they are composed of various monomer units and the ß-1,4 linked backbone contains numerous short side chains that might be linked a-1,2, a-1,3 or a-1,6.  Also some primary cell wall hemicellulose backbones contain ß-1,3 in addition to ß-1,4 linkages.  The sugar monomers of hemicelluloses include glucose, mannose, xylose, arabinose, galactose and 4-O-methyl glucuronic acid.

Pectins are another complex group of polysaccharides that are abundant in primary cell walls and in the middle lamella between all plant cells.  Like hemicellulose, pectin polymers are chemically diverse molecules.  Pectins are acidic and contain a high proportion of D-galacturonic acid residues joined by a-1,4 glycosidic linkages.  Some of the carboxylic acids of the galacturonates are esterified to methanol.  L-rhamnose (a 6-deoxyhexose) residues are usually interspersed throughout the chain.  The linkage of D-galacturonic acid to L-rhamnose is a-1,2 and the linkage from D-galacturonic acid to the next galacturonic acid in the chain is a-1,4.  Side chains are often attached to these rhamnose residues.  The side chains appear to be neutral sugars polymers containing monomers such asL-arabinose or D-galactose.  These types of pectins are known as rhamnogalacturonans.  Neutral pectins are also known which appear to be large branches of the acidic pectins.  The 3 main types are the arabinans, the arabinogalactans and the galactans.  Arabinans are highly branched consisting of a core of a-1,5 arabinosyl (a pentose in the furanose ring form) residues containing a-1,3- and a-1,2-linked arabinosyl side chains.  The arabinogalactans contain ß-1,4-linked galactose chains carrying arabinose residues at the 3 and 6 positions that are further substituted.  Galactans are mostly linear ß-1,4-linked D-galactose polymers with occasional single L-arabinose branches.

Myoinositol could be an intermediate in the formation of hemicellulose and pectins:

At least some of the xyloglucans of primary cell walls are bound to cellulose.  They likely can tether cellulose microfibrils together as illustrated in Fig. 5.15 of Dey & Harborne, 1997:

The first functional model of primary cell walls of plant cells was put forth by Albersheim et al.  It suggests a framework of cellulose microfibrils linked to a xyloglucan-pectin-protein matrix.  In this model the xyloglucan hydrogen-bonded to cellulose as depicted in Fig. 5.15 is also hydrogen-bonded to arabinan and galactan side chains of the pectin polymer and the arabinogalalactan side chain of pectin is attached to serine of the hydroxyproline rich wall glycoprotein (Fig. 5.18 of Dey & Harborne, 1997):

Another model is based on the hypothesis that there are independent polymer networks within the (primary) cell wall; a cellulose-xyloglucan network, a pectin network and a protein network [Carpita & Gibeaut (1993); Fig. 19]:

The spatial arrangement of primary wall polymers is schematically illustrated by McCann & Roberts (1991) (Fig. 5.20 of Dey & Harborne, 1997 above).

We only have time to briefly discuss some other important carbohydrate polymers.

A major structural component in biology is chitin that is very similar to cellulose in primary, secondary and tertiary structure.  The only difference between chitin and cellulose is that the C-2 hydroxyl group of the glucose monomers is replaced by NHCOCH₃ so that the repeating units are N-acetyl-D-glucosamines: 

The ß-1,3 glucan, callose, also similar to cellulose, is an important polymeric component of sieve plates of phloem tubes.  Callose is also produced during wound healing of damaged plant tissues [see Fig. 1 of Delmer and Amor (1995) above].

Another interesting group of structural carbohydrates that form extended hydrogen-bonded ribbons is the alginates of marine brown algae.  These include poly(ß-D-mannuronate) and poly(a-L-guluronate) which are ß-1,4 linked chains of ß-D-mannuronic acid and a-L-guluronic acid.

Marine red algae contain the structural polysaccharide agar, which consists of 2 components, agarose and agaropectin.  Agarose is composed of alternating D-galactose and 3,6-anhydro-L-galactose with side chains of 6-methyl-D-galactose residues.  Agaropectin is like agarose but additionally contains sulfate ester side chains and D-glucuronic acid.  The tertiary structure of agarose is a double helix with a so-called threefold screw axis.  The central cavity of this double helix can accommodate H₂O molecules.  Agarose and agaropectin readily form gels that contain high amounts of H₂O (up to 99.5%).  An agarose double helix: