Final answer:
Platelets, which are cell fragments derived from myeloid stem cells, are responsible for mediating hemostasis, the process that stops bleeding by clot formation.
Step-by-step explanation:
Hemostasis is mediated by platelets, one of the formed elements of blood that are essential for the clotting process. These cell fragments, also known as thrombocytes, arise from myeloid stem cells and break off from megakaryocytes within the bone marrow. Platelets accumulate at the site of blood vessel injury to form a platelet plug, and in conjunction with coagulation factors, they promote the formation of a fibrin clot—a key aspect in the cessation of bleeding.