molecular energy level. (physical chemistry). One of the states of motion of nuclei and electrons in a molecule, having a definite energy, which is allowed by quantum mechanics.1  Facebook.olecular energy level. (physical chemistry). One of the states of motion of nuclei and electrons in a molecule, having a definite energy, which is allowed by quantum mechanics. 1  Facebook.
Air first enters your body through your nose or mouth, which wets and warms the air. (Cold, dry air can irritate your lungs.) The air then travels through your voice box and down your windpipe. The windpipe splits into two bronchial tubes that enter your lungs.
Confidence votes 2.6K. When you breathe in, air enters the body (via mouth or nose) and travels down a tube called the windpipe (aka trachea) and into the lungs. When you exhale, carbon dioxide gas is released. Heres something fun for you to try, take a deep breath (inhale with your nose) and try and imagine oxygen going into the lungs.