This document defines digestion as the complex breakdown of food into forms the body can use for energy. It describes the two types of digestion as chemical and physical. Chemical digestion breaks down food into simpler nutrients through enzymes, beginning in the mouth. Physical or mechanical digestion starts with chewing in the mouth and muscular movements moving food through the digestive tract, supporting chemical breakdown by reducing food size. Both physical and chemical digestion occur at different pH levels throughout the mouth, stomach, and intestines as part of the digestive process.