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.
Yes, blood needs to go into the lungs via the pulmonary artery so gas exchange can occur. This turns the oxygen poor blood in the pulmonary artery into oxygen rich blood which is carried back to the heart via the pulmonary vein. No, then the pathway would be wiped out and you would not be able to breathe.