The chief difference between the erythrocytes of man and frog is
A. Human erythrocytes have more haemoglobin.
B. Human erythrocytes have more nuclei.
C. Human erythrocytes have no nuclei.
D. Human erythrocytes have less haemoglobin.

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Hint: Erythrocytes or red blood cells (RBC) are cells arising from a common myeloid precursor. Haemoglobin protein present in RBCs helps to carry oxygen to all cells of the body.

Complete answer: Human body is a complex structure with many systems like the respiratory system, circulatory system, digestive system, immune system, etc. Each system has its own set of organs and cells working to complete its task. The immune system is a defence mechanism for an organism that protects them from any threat or damage. In humans, the immune system is divided into two parts: the innate immune system (also known as non-specific immunity), where as soon as our body is invaded by foreign objects, an innate immune response occurs, it is rapid and is already present also known as the first line of defence. An adaptive immune system (also known as specific immunity) is a selective response where a specific foreign body is killed by a specific antibody. Hence it is a slow response. All cells present in the blood including red blood cells that carry oxygen, the platelets that trigger blood clotting, and white blood cells of the immune system are derived from one precursor Hematopoietic stem cell (HSC) in the bone marrow. The process of differentiation of hematopoietic stem cells into mature blood cells is known as hematopoiesis. HSC differentiate into myeloid progenitor and lymphoid progenitor which further gives rise to different immune cells including phagocytic cells, antigen-presenting cells, etc. The cellular component of blood contains white immune cells which include dendritic cells, neutrophils, basophils, eosinophils, mast cells, platelets, and erythrocytes (RBCs).
Erythrocytes are myeloid cells having haemoglobin protein. They are present in numerous numbers in blood compared to other components. The function of RBCs is to transport respiratory gases. Erythrocytes in different species have different characteristic features. In humans, the shape of RBCs is a biconcave disc, whereas, in frogs, it has an oval, biconvex shape. The main difference in erythrocytes of humans and frogs is that human RBCs do not have a nucleus and most cell organelles but frog RBCs do have a nucleus present at the centre.
Hence, the correct answer is option C.

Note: In the course of evolution from frogs to humans, denucleation of RBCs has occurred because removal of cell organelles and nucleus resulted in an increased exchange of gas. Thus, RBCs without a nucleus can carry more volume of oxygen.