Question

Why do mature erythrocytes in humans lack nucleus and mitochondria?

Answer 1

Hint: The red blood cells carry oxygen and transport it to the needy tissues. On the other hand, mitochondria are the organelle that uses oxygen for energy production. Also, the nucleus is a heavy organelle and acquires a lot of space.

Complete answer:
Red blood cells are responsible for the transport of oxygen to the needy tissues. This question has two parts to it.
Lack of mitochondria:
Mitochondria are responsible for major energy production and are known as the powerhouse of the cell. It utilizes oxygen for the production of Adenosine Triphosphate (ATP) which in turn provides energy to the cell. Lack of mitochondria in the RBCs ensures no utilization of oxygen for cellular respiration. The amount of oxygen carried by the RBCs is fully transported to the tissues without even a fraction of it getting wasted by the mitochondria of the RBC.
Lack of nucleus:
The only cells in mammals that lack a nucleus are the RBCs. Not only the nucleus but the RBCs are also devoid of the other cell organelles as well, like, Golgi apparatus, Endoplasmic Reticulum, etc. Accommodation of these cell organelles would take a lot of space and the RBC would become heavy.
The absence of these ensures more space provided to the hemoglobin which in turn will carry more oxygen. Also, this provides a biconcave structure to the RBCs for getting transported easily through narrow capillaries and veins. Hence, they can reach all parts of the body without any resistance.
This is the reason why RBCs lack mitochondria and nucleus.

Note:
The absence of mitochondria in mature RBCs ensures the entire amount of oxygen getting transported to the needy tissues in all parts of the body without even a single fraction of it being used for cellular respiration.
The lack of nucleus in the RBCs helps in dual function. Firstly, it increases the space for more hemoglobin to accommodate and increase the oxygen-carrying capacity of the RBCs. Secondly, it maintains the biconcave structure of RBCs for easy transport through narrow capillaries and veins.