Oxygen cycle, oxygen the by product of photosynthesis is inhaled by heterotrophs which aids in cellular respiration and other internal processes and then exhales carbon dioxide.
The oxygen is enhaled and enters through the lungs and passes through an air-blood barrier into the blood in capillaries. In like manner, carbon dioxide passes from blood to the alveoli and exhaled after. The oxygenated blood will then travel from the lungs through the pulmonary veins that pumps blood to the rest of the body.
