cellulosa

Cellulosa, commonly known as cellulose, is a natural polymer composed of β-D-glucose units linked by β-1,4-glycosidic bonds. The linear chains align to form microfibrils, which in turn provide high tensile strength to plant cell walls. It is the most abundant organic polymer on Earth, hydrophilic and insoluble in water, and it occurs primarily in plant tissues as part of a complex matrix with lignin and hemicelluloses.

In plants, cellulose is synthesized at the plasma membrane by cellulose synthase complexes that extrude glucan chains which later crystallize into microfibrils. Similar enzymes in some algae and bacteria also produce cellulose. Natural cellulose exists mainly as crystalline cellulose I, though chemical or thermochemical treatment can convert it to cellulose II or other forms.

Natural occurrence and properties: cellulose is a major structural component of plant cell walls, especially in wood and cotton. Its crystalline regions confer rigidity, while amorphous regions contribute to flexibility. It is insoluble in water and resistant to many chemical attacks, and humans cannot digest it due to the absence of cellulolytic enzymes.

Biological role and digestion: cellulose provides mechanical support, helps determine cell shape, and influences growth. Many animals lack endogenous cellulases and rely on gut microbiota or symbionts to break down cellulose; others cannot digest it at all, making it a form of dietary fiber.

Uses and applications: cellulose is processed for pulp and paper, textile fibers, and regenerated forms such as viscose/rayon and cellophane. Nanocellulose and cellulose nanofibers are used as reinforcing agents in composites and in various high-value products. It also serves as a feedstock for biofuels after pretreatment.