What specialized molecules do red blood cells contain for oxygen transport?

Red blood cells contain hemoglobin, which is the specialized molecule responsible for transporting oxygen throughout the body. Hemoglobin is a protein that binds to oxygen in the lungs and carries it to tissues and organs, where it is released for cellular use. This process is vital for maintaining the body's metabolic functions, as oxygen is crucial for energy production in cells.

In contrast, myoglobin, while also an oxygen-binding protein, is primarily found in muscle tissue and has a different function than hemoglobin. It stores oxygen for use during muscle contractions but is not involved in transportation through the bloodstream. Albumin is a protein in plasma that helps maintain osmotic pressure and transport various substances, but it does not play a role in oxygen transport. Fibrinogen is a key component of blood clotting and is not involved in transporting oxygen.

Thus, hemoglobin is specifically designed for the role of oxygen transport within red blood cells, making it the correct answer.