What do the red blood cells primarily transport in the body?

Red blood cells (RBCs) play a critical role in the body's physiology by primarily transporting oxygen from the lungs to various tissues and organs. They contain hemoglobin, a protein that binds to oxygen, allowing RBCs to effectively carry large amounts of oxygen throughout the bloodstream. In addition to oxygen transport, RBCs are also involved in the transport of carbon dioxide— a waste product of cellular metabolism—back from the tissues to the lungs, where it can be exhaled. This dual function of transporting both oxygen and carbon dioxide is vital for maintaining cellular respiration and overall metabolic processes within the body.

While vitamins, electrolytes, and antibodies are important components of the body, they are transported through other means. For example, vitamins and electrolytes are typically dissolved in plasma or bound to other proteins, and antibodies are part of the immune system, primarily found in the plasma and produced by other types of cells. Thus, the primary role of red blood cells is specifically focused on the transport of gases, making the correct answer clear in the context of their function.