Which statement best describes platelets?

• A. Platelets are nucleated cells involved in gas transport
• B. Platelets are cell fragments that participate in clotting
• C. Platelets are a type of white blood cell
• D. Platelets are proteins that form fibrin directly

Answer: (B)

Platelets are cell fragments produced in the bone marrow from megakaryocytes. They are anucleate, small fragments that circulate and respond quickly to vascular injury. Their main role is in hemostasis: they form a platelet plug at the site of a damaged vessel and provide a phospholipid surface that helps coagulation factors assemble, accelerating the clotting process. They also release granules that recruit more platelets and promote vasoconstriction to limit blood loss. They are not nucleated cells involved in gas transport (that’s red blood cells), nor are they a type of white blood cell, and they do not themselves form fibrin—the clotting protein fibrin is produced from fibrinogen by thrombin, with platelets facilitating the process. Hence, describing platelets as cell fragments that participate in clotting best captures their structure and function.