Final answer:
The oxygen atoms a runner exhales are not the same oxygen atoms she inhaled from the environment. When we inhale, oxygen molecules from the environment enter our lungs and diffuse into the bloodstream. In the cells, oxygen is used in cellular respiration to produce energy.
Step-by-step explanation:
The oxygen atoms a runner exhales are not the same oxygen atoms she inhaled from the environment. When we inhale, oxygen molecules from the environment enter our lungs and diffuse into the bloodstream. In the bloodstream, oxygen binds to hemoglobin in red blood cells and is transported to cells throughout the body. In the cells, oxygen is used in cellular respiration to produce energy. During cellular respiration, oxygen atoms combine with carbon atoms from glucose molecules, producing carbon dioxide as a waste product. This carbon dioxide is then transported back to the lungs and exhaled.