What is the primary function of red blood cells?

The primary function of red blood cells is to carry oxygen from the lungs to all cells in the body. This is achieved through a protein called hemoglobin, which binds to oxygen in the lungs and releases it in the body's tissues. This process is essential for cellular respiration, where cells use oxygen to produce energy. Without efficient transport of oxygen, cells would not be able to function properly, leading to fatigue and a decrease in overall health.

In contrast, the other choices focus on different roles of other components in the blood or immune system. For example, antibodies are produced by white blood cells to help fight infections, which is not a function of red blood cells. Blood clotting is managed by platelets and clotting factors, ensuring wound healing rather than oxygen transport. Nutrient transport is primarily the role of plasma and other cells, not red blood cells, which are specialized for oxygen transportation.