Where does the exchange of carbon dioxide and oxygen with the blood occur
the bronchi
bronchiole
alveolar ducts
alveolar sacs
It seems that you are asking different questions under different names. You can ask more than one question on a post.
Think of it as transportation. Where does the "end of the line" occur?
If that doesn't help, try
http://www.answers.com/topic/air-sac
I hope this helps. Thanks for asking.