Question

How is a molecule of oxygen flowing through the respiratory system like a commuter driving home from work ?

Answer 1

If you pay attention to a commuter, you will notice that the train start from a stations, then collect and drop various people as it stop between stations before it eventually came back to the first station.
So does the Oxygen flow. It started from the lung, transferred to various parts of our body, and came back again to the lungs.