What makes it possible for us to have the sense of smell?

Question

What makes it possible for us to have the sense of smell?

Answer 1

We have neural receptors in our nose.  There are many different types of these receptors and they match specific aromatic molecules.  For example, you have receptors that match floral aromas and some that match putrid aromas, etc.  The exact combination of the mix of aromatic molecules from the odor source is what distinguishes them.  

So, these receptors are stimulated when a molecule attaches to them.  The signal is sent to the brain saying something like, "hey, we smell something that is about 45% this and 12% that and has about 0.1% of that other thing . . . what is it?"  And your brain searches its memory looking for a match to something you've smelled before so you can recognize the smell.