Which carbohydrate is the most abundant organic compound in the terrestrial environment?

• A. Inulin
• B. Cellulose
• C. Dextran
• D. Chitin

Answer: (B)

The greatest amount of organic material on land is built by plants, and the primary carbohydrate in plants is cellulose, the structural polysaccharide in cell walls. Cellulose is a polymer of glucose linked by beta-1,4 bonds, which leads to long, straight chains that hydrogen-bond to form strong, rigid microfibrils. This structural network is essential for plant rigidity and growth, so plants produce vast quantities of cellulose and accumulate it in wood, fibers, and other plant tissues. Because terrestrial biomass is dominated by plant material, cellulose ends up as the most abundant organic compound on land.

Inulin appears as a storage carbohydrate in some plants but is not widespread enough to rival cellulose globally. Dextran is produced by certain bacteria as a microbial exopolysaccharide, not a major component of terrestrial biomass. Chitin is a major component of arthropod exoskeletons and fungal cell walls and is abundant in some environments, but overall terrestrial plant matter dwarfs it, making cellulose more abundant on land.