Which substance is found in red blood cells and is crucial for oxygen transportation?

Hemoglobin is the essential protein found in red blood cells that is responsible for transporting oxygen throughout the body. It binds to oxygen in the lungs and releases it in tissues where it is needed. The structure of hemoglobin allows it to carry up to four oxygen molecules at a time, significantly enhancing the efficiency of oxygen delivery compared to other substances.

Myoglobin, while also a heme-containing protein that binds oxygen, is located primarily in muscle tissues and serves to store oxygen rather than transport it through the bloodstream like hemoglobin. Albumin is a protein in blood plasma that helps maintain oncotic pressure and transport various substances, but it is not involved in oxygen transport. Globulins are a group of proteins in the blood that serve various immune functions and transport tasks but do not play a direct role in the transportation of oxygen like hemoglobin does.