Which statement best describes cellulose digestion in this context?

• A. Cellulose is digestible by human enzymes
• B. Bacteria can break down cellulose in the digestive system
• C. Cellulose is converted to starch by amylase
• D. Cellulose is not found in plants

Answer: (B)

Cellulose digestion depends on microbes in the digestive tract. Humans don’t have the cellulase enzyme needed to break the beta-1,4 linkages in cellulose, so our own digestive enzymes can’t digest it. Instead, gut bacteria can ferment cellulose to some extent, producing short-chain fatty acids and gases. In many animals, like cows or termites, specialized microbes do a lot of the work, but in humans the contribution is limited to microbial fermentation rather than true enzymatic digestion by the host. That’s why the best description is that bacteria can break down cellulose in the digestive system. Cellulose isn’t converted to starch by amylase, and cellulose is indeed found in plants; also, humans aren’t able to digest cellulose with our own enzymes.