Final answer:
Mechanical digestion begins with chewing in the mouth, where the teeth break down food and the tongue forms it into a bolus, and continues with the churning of food in the stomach.
Step-by-step explanation:
If I were describing the process of mechanical digestion to my lab partner, the most accurate statement would be that during mechanical digestion, the teeth break down food into small pieces, and the tongue manipulates it into a bolus. This statement reflects the physical aspect of mechanical digestion as it begins in the mouth with the act of chewing. Saliva from the salivary glands does contribute to this process by moistening the food, but it also initiates chemical digestion through the action of enzymes like amylase, which starts the breakdown of carbohydrates. Mechanical digestion continues in the stomach where food is mixed with digestive juices, a process known as churning, which forms largely into a mixture called chyme. This is distinct from chemical digestion which involves enzymes, acids, and other secretions breaking down food on a molecular level.