Answer:
The correct answer is - they lack a nucleus.
Explanation:
Red blood cells or erythrocytes are anucleated, biconcave, and small specialized cell that produce in bone marrow and lacks the mitochondria at maturity. RBC plays very important role to carry oxygen from lungs to deliver it to the various parts of the body and carry out carbon dioxide from various part to back to the lungs.
Due to lack of the cell organelles and nucleus, these cells are smaller in size. The size of RBC circulate throughout the body through narrow vessels due to its specific size and shape that provide it space for hemoglobin that binds with oxygen.
Thus, the correct answer is - they lack a nucleus.
