Final answer:
Mechanical digestion is the physical breakdown of food starting in the mouth and continuing in the stomach. Chemical digestion breaks down complex food molecules into smaller, simpler molecules, primarily occurring in the small intestine.
Step-by-step explanation:
Mechanical digestion refers to the physical breakdown of food into smaller pieces. This process starts in the mouth where mastication, or chewing, takes place. The food is then mixed with saliva, which not only begins the chemical breakdown but also makes the food easier to swallow. The mechanical digestion continues in the stomach, as the muscular walls churn the food, further breaking it down into smaller pieces without changing its chemical nature.
Chemical digestion, on the other hand, involves the breaking down of complex food molecules into smaller, absorbable nutrient molecules through chemical reactions. This process also begins in the mouth with enzymes present in saliva but mainly takes place in the small intestine, where a variety of enzymes secreted by the pancreas and liver mix with the food to facilitate nutrient absorption into the bloodstream.
The distinction between these two types of digestion is essential for the body to efficiently process food and extract necessary nutrients. Mechanical digestion increases the surface area of the food for enzymes to work more effectively during chemical digestion, thereby ensuring the body receives the nutrients it requires from the food we eat.