Final answer:
Not all taste sensations employ ionotropic receptors; salty and sour tastes do, but sweet, bitter, and umami tastes use G-protein coupled receptors.
Step-by-step explanation:
The answer to the student's question about whether all taste sensations employ ionotropic receptors is false. While it is true that the sensations for salty and sour tastes are initially sensed through ion channels on the taste buds, the other tastes, such as sweet, bitter, and umami, involve a different mechanism. These tastes use G-protein coupled receptors rather than ionotropic receptors. Specifically, the salty taste is detected through the entry of sodium ions, while the sour taste results from hydrogen ions affecting ion channels. On the other hand, sweet, bitter, and umami tastants bind to G-protein coupled receptors which then lead to cell depolarization through a series of intracellular events.