The correct option is RBC.
Explanation
Human blood cells exhibit distinct morphological adaptations that suit their specific physiological functions. The presence or absence of a nucleus and the specific shape of the cell are critical identifiers for different types of blood cells.
Detailed Analysis:
- Red Blood Cells (RBCs): Mature mammalian erythrocytes (RBCs) are characteristically enucleated, meaning they lack a nucleus. They also lack other organelles such as mitochondria and ribosomes. Their shape is a biconcave disc. This specific geometry increases the surface area-to-volume ratio, facilitating efficient gas exchange (oxygen and carbon dioxide) and allowing the cells to deform and pass through narrow capillaries.
- White Blood Cells (WBCs): Leukocytes are nucleated cells. They possess a nucleus which may be lobed (as in granulocytes) or large and round (as in lymphocytes). Their shape is generally irregular or amoeboid, allowing for motility.
- Platelets: These are cell fragments derived from megakaryocytes. While they are non-nucleated, they are typically small and discoid or irregular in shape, not biconcave.
- Neurons: Nerve cells possess a distinct cell body (soma) containing a nucleus, along with extensions known as axons and dendrites. They are not biconcave.
Key Takeaway:
Mature mammalian Red Blood Cells are unique in being enucleated and biconcave, adaptations that maximize space for haemoglobin and enhance oxygen transport efficiency.