Final answer:
Mechanical digestion is the physical breakdown of food into smaller pieces, while chemical digestion is the chemical breakdown of food molecules into nutrients.
Step-by-step explanation:
Mechanical digestion is the physical process in which food is broken down into smaller pieces without becoming chemically changed. It occurs mainly in the mouth and stomach. Chemical digestion, on the other hand, is the chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by the body.