Short answers, pulled from the story.
Lucretius proposed that different odors arise from atoms with unique shapes and sizes. He suggested these microscopic particles stimulate the olfactory organ to create a scent experience.
Linda B. Buck and Richard Axel received the Nobel Prize in 2004 for cloning olfactory receptor proteins. Their research proved that each odor molecule fits into specific receptors like a key in a lock.
Humans carry far fewer active odor receptor genes than other primates or mammals. Mammals possess about one thousand genes dedicated to this reception process but only a portion function correctly in any given species.
Signals travel through cranial nerve I directly to the olfactory bulb and then project information to five major brain regions including the amygdala and piriform cortex. The orbitofrontal cortex mediates conscious perception while the entorhinal cortex links odors to emotional memory.
Bloodhounds possess noses ten million times more sensitive than human counterparts according to experimental findings. Grizzly bears detect food sources up to eighteen miles away using their powerful sense of smell.
The odorant receptor OR5A1 determines the ability to smell beta-ionone found in many foods. Individuals with specific variants of OR2J3 detect grassy odors known as cis-3-hexen-1-ol.