What is the primary function of red blood cells?

The primary function of red blood cells is to transport oxygen from the lungs to the tissues and organs throughout the body. This vital process is carried out by hemoglobin, a protein found within red blood cells that binds to oxygen molecules as the blood circulates through the lungs. Once the blood reaches the body's tissues, hemoglobin releases the oxygen, allowing it to be utilized for cellular metabolism and energy production.

While red blood cells do play a role in transporting carbon dioxide from the tissues back to the lungs for exhalation, their main function revolves around oxygen transport. This process is critical for maintaining the body's overall functionality and supporting life. Other options like transporting nutrients or combating infections are tasks primarily associated with different components of the blood, such as plasma and white blood cells, respectively. Thus, the essential role of red blood cells lies in their ability to efficiently carry oxygen, a necessity for all cellular functions.