What is the carbohydrate substance common in the cell walls of many organisms?

• A. Cellulose
• B. Glycogen
• C. Starch
• D. Chitin

Answer: (A)

Cellulose is the structural carbohydrate most common in the cell walls of many organisms, especially plants and some algae. Its glucose units are linked by beta-1,4 bonds, which create straight, unbranched chains that can align and form strong, fibrous microfibrils. These microfibrils intertwine and are toughly reinforced by hydrogen bonding, giving plant cell walls rigidity and the ability to withstand turgor pressure as the cells grow. This structural role is different from the other carbohydrates listed: glycogen and starch are primarily energy storage polymers, with branched structures that make them efficient for quick energy release rather than building rigid walls. Chitin plays a similar structural role in fungi and in the exoskeletons of some arthropods, but it is not as universally used for cell walls across many organisms as cellulose.