The molecule within red blood cells that binds oxygen to enable transport is what?

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

Answer: (C)

Hemoglobin is the molecule inside red blood cells that carries oxygen. It’s a four-part protein with heme groups, each containing iron that can reversibly bind one O2 molecule. In the lungs, oxygen loads onto iron, forming oxyhemoglobin, and as blood travels to tissues, oxygen is released where it’s needed. Because one hemoglobin can bind up to four oxygen molecules, it’s an efficient transport system for oxygen throughout the body. Hemoglobin’s ability to change its affinity for oxygen when one molecule binds (cooperative binding) helps it pick up oxygen in the lungs and release it in tissues where it’s required.

Other options don’t fit this transport role: myoglobin stores oxygen in muscle tissue and binds a single O2 molecule, not for transport in the bloodstream; albumin is a plasma protein that carries various substances but does not bind oxygen for transport; fibrin is involved in blood clotting, not oxygen transport.