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.
In emphysema, the lung tissue gets weak, and the walls of the air sacs (alveoli) break down. Normally, oxygen from the air goes into the blood through these air sac walls. In a person with emphysema, the ruined air sac walls means less oxygen can pass into the blood.