Which nutrient is primarily responsible for oxygen transport within the bloodstream?

Hemoglobin is primarily responsible for oxygen transport within the bloodstream. This protein, found in red blood cells, binds to oxygen in the lungs and carries it through the bloodstream to the tissues and organs where it is needed for cellular respiration and energy production. Hemoglobin's ability to effectively pick up oxygen and release it as needed is crucial for maintaining the body's metabolic functions.

While myoglobin, which is similar to hemoglobin, also plays a role in oxygen storage within muscles, it does not transport oxygen in the bloodstream. Iron is a vital component of hemoglobin, necessary for its function and formation, but it does not transport oxygen by itself. Albumin, on the other hand, is a protein that helps maintain osmotic pressure in the blood and transports various substances, but it is not involved in oxygen transport. Thus, hemoglobin is the correct answer, as it directly facilitates the movement of oxygen from the lungs to the body's tissues.