Which statement about mature mammalian red blood cells is true?

• A. They have a nucleus
• B. They lack a nucleus
• C. They are the primary site of protein synthesis
• D. They are able to divide

Answer: (B)

Mature mammalian red blood cells are anucleate. During development in the bone marrow, they eject their nucleus to maximize hemoglobin content and to become highly flexible for passing through narrow capillaries. Lacking a nucleus—and with no mitochondria or ribosomes—they cannot carry out transcription or translation or divide. They rely on glycolysis for energy and have a limited lifespan, which fits their primary role of transporting oxygen. This is why the true statement is that they lack a nucleus.