Biological Systems MCAT Practice Exam

Fibrin is the correct answer because it plays a crucial role in the stabilization of a platelet plug during the clotting process. When a blood vessel is damaged, platelets aggregate at the site of injury and form a temporary plug. This initial structure is strengthened by fibrin, which is created from fibrinogen in response to the activation of the clotting cascade, particularly by thrombin. Thrombin converts soluble fibrinogen, a plasma protein, into insoluble fibrin strands. These strands weave through the platelet plug, effectively anchoring the platelets together and creating a more stable and durable clot that helps prevent further bleeding until the vessel is repaired. While fibrinogen and thrombin are key players in the clotting process, it is the fibrin that provides the actual structural support, securing the platelet plug and helping to facilitate the healing process.