And that's precisely why oxygen will move down its pressure gradient from the alveoli of the lungs and it into the capillaries of our lungs. Now, the next question is what exactly happens to our oxygen as soon as the oxygen arrives in the blood plasma of the capillaries? Recall that blood plasma consists predominantly of water. And that makes our blood plasma a polar substance. Now, diatomic oxygen, as it exists in our blood in the atmosphere, is a nonpolar substance. It's a nonpolar molecule.