Physiotherapy Question:

With the help of the red blood cells in your bloodstream.
Your red blood cells are like box cars on train tracks.
They show up at the sacs at just the right time, ready to
trade in old carbon dioxide that your body's cells have
made for some new oxygen you've just breathed in. In the
process, these red blood cells turn from purple to that
beautiful red color as they start carrying the oxygen to
all the cells in your body.