Starch in industry: Amylopectin's branched structure holds water well; used in food thickening, paper sizing, and textile finishing. Amylose forms helical complex with iodine (blue-black colour) — the basis of the iodine test for starch.

Cellulose applications: Although humans cannot digest cellulose, it is industrially important: cotton (pure cellulose), paper pulp, rayon (regenerated cellulose), cellophane, and gun cotton (cellulose nitrate). Its $\beta$-1,4 linear structure gives high tensile strength.

Glycogen as energy reserve: Glycogen is stored in liver and muscle. During fasting or exercise, glycogen is hydrolysed (glycogenolysis) to release glucose for energy. Its highly branched structure allows rapid, simultaneous release from many chain ends.

Sucrose in food industry: Sucrose (table sugar) is the world's most produced organic chemical. Its non-reducing nature makes it chemically stable during storage and heating (does not undergo Maillard browning). Hydrolysis of sucrose by the enzyme invertase gives an equimolar mixture of glucose and fructose called invert sugar (sweeter than sucrose; used in confectionery).

Proteins in biotechnology: Protein denaturation is exploited in food processing (cooking eggs, pasteurisation). Enzyme denaturation by heat is the basis of sterilisation. Recombinant insulin (human sequence expressed in bacteria/yeast) is produced by biotechnology.

Vitamin synthesis: Vitamin C (ascorbic acid) is manufactured industrially via the Reichstein process from sorbitol. Synthetic vitamins A and D are produced for fortification of food and pharmaceutical use.

Nucleic acid applications: DNA is the basis of genetic engineering, PCR diagnostics (COVID-19 tests), gene therapy, and forensic DNA fingerprinting. The G–C hydrogen bonding advantage (3 H-bonds) is exploited in primer design for PCR — GC-rich primers have higher annealing temperatures and greater specificity.

Fermentation: Yeast converts glucose → ethanol + CO$_2$ (anaerobic fermentation). Lactic acid bacteria convert glucose → lactic acid (yoghurt production). Both rely on the glycolysis pathway, beginning with the monosaccharide glucose ($C_6H_{12}O_6$).

Amino acid production: Glutamic acid (monosodium glutamate, MSG) is produced industrially by fermentation. Lysine and tryptophan are added to animal feed as essential amino acid supplements.

Biopolymers vs synthetic polymers: Proteins, polysaccharides, and nucleic acids are natural biopolymers with precise sequence and stereochemistry. Understanding their linkages (glycosidic, peptide, phosphodiester) is relevant to designing synthetic polymer mimics.