Final answer:
Stretch-gated mechanoreceptors are the least likely to respond to a chemical inhibitor because they are primarily sensitive to physical stimuli like pressure and stretch, unlike G-protein-coupled receptors and ionotropic receptors that are designed to respond to chemical stimuli.
Step-by-step explanation:
The question asks which type of sensory receptor would be the least likely to respond to a chemical inhibitor. To answer this, we need to consider the types of receptors and how they respond to stimuli. Receptors such as G-protein-coupled receptors for olfaction and taste are specifically designed to respond to chemical stimuli. These include both the G-protein-coupled olfactory receptor and the G-protein-coupled photoreceptor mentioned in the options, which indeed are affected by chemicals that bind to them and subsequently activate a G-protein.
Similarly, ionotropic taste receptors also respond to chemical stimuli; however, they are directly gated by these chemicals as opposed to G-protein-coupled receptors that require a series of intracellular signaling events. In contrast, stretch-gated mechanoreceptors are primarily sensitive to physical stimuli, such as pressure and stretch, rather than chemical stimuli. Thus, a mechanoreceptor would be the least affected by a chemical inhibitor compared to receptors that are directly involved in chemical signaling.