Which of the following happens in the lungs?

Which of the following happens in the lungs?

 Gases move up a concentration gradient.
 Gases move by bulk flow into and out of the circulation.
 Blood loses all of its carbon dioxide.
 Air loses all of its oxygen.
 Some of the oxygen in the air moves into the blood, and some of the carbon dioxide in the blood moves into the air.

Post Merge: 7 years ago

Some of the oxygen in the air moves into the blood and some of the carbon dioxide in the blood moves into the air... seems correct.   However  the Audesirk text alludes to a concentration gradient also,  so wonder if there is any evidence for that too.