blood-in-vesselQ: What is the name of the complex molecule that carries oxygen in the blood and gives blood its characteristic red color? A: Hemoglobin Red Blood Cells (RBC) are like a bus that delivers the oxygen.  There are receptor sites on the RBC called hemoglobin, which are like seats on the bus.  When the RBC’s arrive at the lungs, they are surrounded by oxygen, and if an oxygen molecule bumps up against the hemoglobin, it will become attached.  Ultimately, a healthy RBC will have all of its “seats” filled with oxygen. RBC