[mass]

(-)-Carvone occurs in spearmint and its enantiomer is found in caraway seed. To the human sense of smell these two enantiomers have different odours. What conclusions can be drawn about the human olfactory recepetor site.

I have written that the human olfactory receptor site is chiral. Therefore, only one enantiomer fits into 1 receptor site whilst the other one fits into a different receptor site.

Is this a correct statement?

[movies]

That is one possible explanation.  Another possibility is that both enantiomers of carvone interact with the same chiral receptor site, but in different ways.

How would you describe the stereochemical relationship between the two complexes of receptor and carvone?

[mass]

if they reacted the same way, wouldn't the smell be the same?

[limpet chicken]

I imagine its the same receptor, but that one stereoisomer changes the conformation of the receptor protein in a different way to the other isomer.

This happens very frequently, biochemically speaking, thus D-methorphan (dextromethorphan, DXM), is a cough suppressant, acting on the NMDA receptor (sigma receptor perhaps, like PCP? I don't know that one for sure), but the other isomer, laevo-methorphan acts as a fairly potent mu opioid agonist.

[movies]

Think about it this way: suppose you have a chiral carboxylic acid that is enantiopure, for example (R)-mandelic acid.  Then, suppose that I mix that enantiopure acid, in two different flasks, with each enantiomer of a chiral base, like (R)- and (S)-sec-phenethylamine.  In each case you will get a rapid acid/base reaction as the amine deprotonates the acid to form a salt that will likely precipitate.  So the same general reaction has occurred in each case.

Now think about the forms of the salts that you have formed.  Are they identical?

In the same way, think about the receptor in your nose as the carboxylic acid and the carvone enantiomers as the amine enantiomers, it's the same thing!

(I actually don't know whether your initial explanation or the one that I have provided is the correct one in this case, but they are both reasonable possibilities.)