Which blood component is derived from myeloid stem cells and is involved in clotting but is not a leukocyte?

• A. Erythrocyte
• B. Thrombocyte
• C. Monocyte
• D. Lymphocyte

Answer: (B)

Platelets (thrombocytes) are the blood component derived from the myeloid lineage that drives clotting, yet they are not leukocytes. They come from megakaryocytes in the bone marrow and are small, anucleate fragments that quickly form a platelet plug at injury sites and support the coagulation cascade by releasing granule contents and providing surfaces for coagulation factors. Erythrocytes also come from the myeloid lineage but their role is oxygen transport, not clotting. Monocytes and lymphocytes are leukocytes, involved in immune functions rather than primary hemostasis. So the component that fits all parts of the description is the platelet.