What is the primary function of red blood cells?

• A. Oxygen and carbon dioxide transport via hemoglobin
• B. Produce antibodies
• C. Carry urine
• D. Filtration of plasma

Answer: (A)

Red blood cells are specialized to carry gases. Their main job is to shuttle oxygen from the lungs to every tissue and to bring carbon dioxide, a waste product of metabolism, from tissues back to the lungs for exhalation. This is achieved by hemoglobin, the protein inside red blood cells that binds O2 and CO2. In the lungs, oxygen binds to the iron in hemoglobin and is released where it’s needed; carbon dioxide from tissues is carried back partly bound to hemoglobin and partly as bicarbonate in plasma after conversion by carbonic anhydrase, then released in the lungs to be exhaled. The other options don’t fit because antibodies are produced by certain white blood cells, while urine transport and plasma filtration are functions of the kidneys.