When you inhale (breathe in), air enters your lungs, and [[1]] from that air moves to your blood. 

When you inhale (breathe in), air enters your lungs, and oxygen from that air moves to your blood. 

At the same time, carbon dioxide, a waste gas, moves from your blood to the lungs and is exhaled (breathed out). 

This process, called gas exchange, is essential to life.