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How do cellulose, starch, and glycogen differ in their functions?

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A biochemical flowchart shows the metabolic pathways for carbohydrate utilization, including glycolysis, the pentose phosphate pathway, and the tricarboxylic acid (TCA) cycle. The diagram traces the conversion of glucose, fructose, and glycerol through various intermediates, leading to energy production, carbon dioxide release, and biosynthesis of amino acids and porphyrins. Key steps and branches are labeled, with colored boxes highlighting biosynthetic outputs. — Carbohydrate Pathways for the utilization of carbohydrates.

Cellulose, starch, and glycogen are all polysaccharides composed of glucose units, but they serve distinct biological roles based on their structures.123

Structural and Functional Differences

Cellulose: This is a structural polysaccharide that serves as the primary component of plant cell walls. Its linear chains of glucose units pack tightly into fiber-like arrangements, providing significant structural stability to plants. While it is the most abundant organic compound, it is generally nondigestible by humans.234
Starch: Starch functions as the major energy-reserve polysaccharide in plants. It consists of two components: amylose (linear) and amylopectin (branched). Plants store starch in granules, which can be broken down into glucose to provide energy.13
Glycogen: Glycogen is the primary carbohydrate storage form in animals, found mainly in the liver and muscles. It is a highly branched, compact molecule that allows for rapid breakdown into glucose during periods of stress or physical activity, serving as an immediate energy reserve.154