Both mechanical and chemical digestion begin in the mouth, making this the correct answer.
Mechanical digestion starts when food is physically broken down by the teeth as they chew and grind it into smaller pieces. This action increases the surface area of the food, making it easier for enzymes to interact with the food during chemical digestion.
Chemical digestion in the mouth occurs primarily through the action of saliva, which contains enzymes such as amylase that begin to break down carbohydrates into simpler sugars. This dual process is essential for preparing food for further digestion and absorption in the gastrointestinal tract.
The other options do not encompass the full range of digestion that occurs in the mouth. Mechanical digestion alone doesn't account for the enzymatic breakdown facilitated by saliva, while chemical digestion alone overlooks the importance of the mechanical aspects of chewing. Therefore, both processes are crucial and occur concurrently in the mouth.