Which protein primarily transports oxygen in the bloodstream?

• A. Hemoglobin
• B. Myoglobin
• C. Albumin
• D. Fibrinogen

Answer: (A)

Oxygen transport in the blood relies on a protein that can reversibly bind oxygen and release it where needed. Hemoglobin, located in red blood cells, has four heme groups with iron that bind oxygen in the lungs to form oxyhemoglobin and release it in tissues where oxygen is scarce. This cooperative binding and regulation (influenced by factors like pH and CO2) makes hemoglobin highly effective at picking up and delivering oxygen throughout the body.

Myoglobin, by contrast, stores oxygen in muscles and releases it under high demand but does not carry oxygen through the bloodstream. Albumin moves many substances and helps maintain blood’s osmotic pressure but does not bind oxygen significantly. Fibrinogen is involved in blood clotting, not oxygen transport.

So, the protein that primarily transports oxygen in the bloodstream is hemoglobin.