How does the blood get oxygen into it?

Answer 1

You breathe. When you breathe, air comes in through your nose. It goes into your lungs. In your lungs are thin small sacks. Air goes on one side, blood on the other. Air filters through the little sacks. The Hemoglobin in your blood gets oxygen from that air that filters through those little sacks in your lungs. Carbon dioxide and a few other gasses are dissolved or carried by your blood stream. They diffuse out through those little sacks. When you breathe out, you get rid of waste gasses, mainly carbon dioxide.