Final answer:
Hemoglobin is the protein that contains iron and binds oxygen for transport in the bloodstream, essential for carrying oxygen to cells and carbon dioxide to the lungs, and gives red blood cells their color.
Step-by-step explanation:
The protein that binds oxygen for transport in the bloodstream, which is a necessary component containing iron, is hemoglobin. Hemoglobin is a complex protein with a quaternary structure that consists of four subunits, two alpha and two beta, each harboring an iron ion. The iron's oxidation state alternates between +2 and +3 as it binds and releases oxygen, causing the hemoglobin molecule to change its three-dimensional shape accordingly. It is this mechanism that facilitates the transport of oxygen from the lungs to peripheral tissues and the return of carbon dioxide to the lungs for exhalation.
Moreover, the iron found in hemoglobin also contributes to the distinctive red color of red blood cells. The efficient transport of oxygen throughout the body is crucial and is primarily made possible because of the iron within the hemoglobin. Thus, when presented with the options of hemoglobin, myoglobin, collagen, and keratin, the correct answer is hemoglobin, the principal component of red blood cells.