Question

Adult human RBCs are enucleated. Which of the following statement(s) is/are the most appropriate explanation for this feature?
(a) They do not need to reproduce.
(b) They are somatic cells.
(c) They do not metabolize.
(d) All their internal space is available for oxygen transport.
(A) (b) and (c)
(B) Only (d)
(C) Only (a)
(D) (a), (c), and (d)

Answer 1

Hint: Mammalian erythrocytes are typically biconcave discs shaped, flattened, and depressed in the center. The RBCs are of specific shape so that it helps in the blood flow easily inside the large vessels and the shape also varies depending upon the organisms.

Complete solution:
Human red blood cells (RBCs), or erythrocytes, are disc-shaped under physiological conditions. More specifically, they are biconcave in shape. The shape of these cells helps in the efficient transport through narrow blood vessels. RBCs are the constituents of the blood and act as the connective tissue. Red blood cells (RBCs), are also known as red blood corpuscles, haematodes, erythroid cells, or erythrocytes. The main role of red blood cells is in transporting oxygen to the body tissues through the blood flow via the circulatory system. In the cytoplasm of red blood cells is hemoglobin, which is an iron-containing biomolecule present that can bind oxygen and is responsible for the red color of the red blood cells and the blood of humans. A single human red blood cell contains approximately 280 million hemoglobin molecules. The cell membrane of RBCs is composed of basic biomolecules which are proteins and lipids, and this structure provides properties essential for physiological cell function such as deformability and stability.
On average, new erythrocytes per second produced in human adults are around 2.4 million. The red blood is synthesized inside the bone marrow and for about 100–120 days they circulate in the body then they get recycled through macrophages as their components become dead. The life span of RBC in the newborn is usually seen between sixty to a hundred days. The fact is that the number of RBCs in a newborn is more than the normal range in the newborn, many RBCs travel from the umbilical cord to the infant and even a baby can get extra RBCs from its twin if present.

So, the correct answer is ‘Only (d)’.

Note:
RBCs are formed in the red bone marrow of bones and the old and damaged cells are eliminated or recycled by the spleen and the liver. Hemoglobin transports almost 98 % of oxygen through the body while the remaining oxygen is dissolved and is transported via plasma.