Cellulose is the most abundant organic polymer on Earth, a linear polysaccharide composed of β-1,4-linked D-glucose units forming the primary structural component of plant cell walls. It provides mechanical strength and rigidity to plants. Humans lack the enzymes to digest it, making it an important source of dietary fiber that promotes gut health and regularity. In food applications, it serves as an insoluble fiber, thickener, and stabilizer in products like baked goods and low-calorie foods. Industrially, it is used in paper, textiles, and as a precursor for derivatives like carboxymethyl cellulose. It is biodegradable and renewable.