Reactions that occur in the lungs are considered _____ of systemic gas exchange.

The correct choice highlights that reactions occurring in the lungs are essentially the reverse of the systemic gas exchange that takes place in the tissues of the body. During systemic gas exchange, oxygen (O2) is delivered to tissues while carbon dioxide (CO2) is taken up and subsequently transported back to the lungs.

In the lungs, however, the process is inverted: CO2 is expelled from the blood into the alveoli to be exhaled, while O2 is absorbed from the alveoli into the blood. This reverse action ensures that the body maintains effective gas exchange, constantly replenishing the oxygen supply and removing carbon dioxide. Thus, the reactions in the lungs complement the systemic exchanges but are fundamentally opposite in their objectives and mechanisms.