A colony of corals responds to a small amount of meat extract in seawater by extending its coral polyps and their tentacles in search of food; a solution of a single type of amino acid can stimulate this response. Conversely, a small amount of seawater in which corals were crushed will stimulate a defensive retraction of the coral polyps. Humans also react strongly to certain chemical stimuli. When you smell freshly baked bread you salivate and feel hungry, and when you smell rotting meat you feel nauseated.
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Many different chemoreceptors can be activated in different combinations and to different degrees, enabling discrimination of an enormous number of odorant and pheromone molecules.
Five classes of taste chemoreceptors have different mechanisms of membrane depolarization.
All animals receive information about chemical stimuli through chemoreceptors, which are receptor proteins that bind to specific molecules—