What do red blood cells primarily contain?

Red blood cells, or erythrocytes, primarily contain hemoglobin, which is a protein responsible for transporting oxygen from the lungs to the rest of the body and returning carbon dioxide from the body back to the lungs. Hemoglobin binds to oxygen molecules and allows red blood cells to carry oxygen efficiently through the bloodstream. This is crucial for maintaining the body’s metabolic functions and overall health.

Other components listed, such as platelets, plasma, and white cells, serve different roles in the blood. Platelets are involved in blood clotting, plasma is the liquid component that carries cells and nutrients, and white cells are part of the immune system. While they are all important to the circulatory and immune systems, they do not play the primary role of oxygen transport that is characteristic of red blood cells and hemoglobin.