Short lifespan of mammalian erythrocytes due to absence of nucleus

The correct answer to the given question is option 'C', which states that mammalian erythrocytes have a short lifespan due to the absence of a nucleus. This absence of a nucleus is a key characteristic of mature mammalian red blood cells (RBCs) and plays a significant role in their function and lifespan.

Explanation:

Erythrocyte structure and function:
- Erythrocytes, commonly known as red blood cells (RBCs), are specialized cells responsible for transporting oxygen from the lungs to the tissues and removing carbon dioxide from the tissues back to the lungs.
- Mature mammalian RBCs are biconcave disc-shaped cells that lack most organelles, including the nucleus. Their primary component is the protein hemoglobin, which binds to oxygen and helps in gas exchange.
- The absence of a nucleus allows more space for hemoglobin, making RBCs efficient oxygen carriers.

Short lifespan of erythrocytes:
- The lifespan of mammalian erythrocytes is relatively short, typically around 120 days.
- The absence of a nucleus is one of the reasons for their limited lifespan.
- Without a nucleus, RBCs are unable to synthesize new proteins or repair damaged ones. They also lack the ability to divide and reproduce.
- Over time, RBCs undergo wear and tear, accumulate damage, and become less flexible, leading to their removal from circulation by the spleen and liver.
- The removal of old or damaged RBCs is essential to maintain the overall health and functionality of the blood.

Role of the nucleus:
- The nucleus is a vital organelle present in most cells, responsible for containing the cell's DNA and controlling cellular activities.
- In mature mammalian RBCs, the absence of a nucleus allows for increased space for hemoglobin, enhancing their oxygen-carrying capacity.
- However, this lack of a nucleus also means that RBCs cannot repair themselves or synthesize new proteins to maintain their structure and function.
- Without the ability to regenerate or repair, RBCs become more susceptible to damage and degradation over time, leading to their limited lifespan.

Conclusion:
The absence of a nucleus in mammalian erythrocytes is a crucial factor contributing to their short lifespan. While this absence allows for increased hemoglobin content and efficient oxygen transport, it prevents the RBCs from repairing themselves or synthesizing new proteins. Over time, the accumulated damage and wear and tear lead to the removal of old or damaged RBCs from circulation, ensuring the overall health and functionality of the blood.