Final answer:
Salivary amylase is less active in the stomach than in the mouth because the acidic stomach environment inactivates the enzyme, thereby stopping the digestion of carbohydrates.
Step-by-step explanation:
Salivary amylase is an enzyme that begins the digestion of carbohydrates in the mouth by breaking down starch into sugars like maltose and dextrins. This enzymatic activity occurs optimally at a pH of around 6.9, with the aid of activators such as Ca++ and Cl¯. In the acidic environment of the stomach, which has a pH of approximately 2 due to the secretion of hydrochloric acid (HCl), salivary amylase is inactivated. This change in pH, along with the activation of pepsinogen into pepsin, leads to the hydrolysis and deactivation of amylase, thus ceasing carbohydrate digestion in the stomach.