Which statement correctly distinguishes mechanical digestion from chemical digestion?

• A. Mechanical digestion uses enzymes
• B. Mechanical digestion physically breaks food into smaller pieces; chemical digestion uses enzymes to break chemical bonds
• C. Mechanical digestion occurs in the stomach; chemical digestion occurs in the mouth
• D. Mechanical digestion increases chemical energy

Answer: (B)

Mechanical digestion is the physical breakdown of food into smaller pieces, increasing surface area for enzymes to work. Chemical digestion, on the other hand, uses enzymes to break chemical bonds within those molecules, yielding smaller, soluble units that can be absorbed.

The correct statement captures this distinction: mechanical digestion physically fragments the food, while chemical digestion relies on enzymes to break chemical bonds. For example, chewing and stomach churning are mechanical steps, whereas enzymes like amylase and proteases drive the chemical changes.

Why the other ideas don’t fit: enzymes aren’t used in mechanical digestion—enzymes are the agents of chemical digestion. Saying mechanical digestion occurs in the stomach and chemical digestion in the mouth oversimplifies and isn’t accurate, since both processes can occur in multiple regions (mechanical in the mouth and stomach; chemical begins in the mouth and continues in the stomach). Finally, mechanical digestion doesn’t increase chemical energy; energy comes from metabolic processes, not from physical fragmentation.