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.
When the air reaches the lungs, some of this oxygen is transferred from the lungs to the blood, and is then transported throughout the body to be used for energy. In addition, the blood contains some carbon dioxide (a waste product) that is transferred to the air in the lungs, which is then exhaled.