Final answer:
The tongue's taste buds, which contain gustatory cells, have the highest sensitivity to sweet stimuli, and these cells are activated by sweet substances binding to G protein-coupled receptors.
Step-by-step explanation:
The area of the mouth with the highest sensitivity to sweet stimuli is the taste buds located on the tongue. The tongue is equipped with various types of papillae, each containing taste buds responsive to different taste modalities. According to the provided information, gustatory cells within these taste buds are activated by sweet substances like monosaccharides (e.g., glucose, fructose) and artificial sweeteners (e.g., aspartame, saccharine, sucralose) when they bind to G protein-coupled receptors. This interaction initiates a signal transduction system that leads to the depolarization of gustatory cells and the perception of sweetness. Interestingly, the sensitivity to taste, including sweetness, can vary among individuals due to genetic differences, as discussed by Dr. Danielle Reed of the Monell Chemical Senses Center.