Final answer:
In a tube without anticoagulant, the blood will clot, consuming coagulation factors and leaving serum, which is the liquid part of the blood after blood cells and clotting factors have been removed by clot formation.
Step-by-step explanation:
A tube without anticoagulant will contain blood that can clot, which means it primarily contains serum upon clotting.
Blood clotting is a hemostatic process involving vascular spasm, the formation of a platelet plug, and the coagulation cascade, leading to the transformation of fibrinogen into fibrin, creating a clot. When blood is drawn into a tube without an anticoagulant, the clotting factors in the plasma will act to form a clot, leaving serum after the coagulation factors have been consumed. Serum is, therefore, the component of blood that is present in a tube without anticoagulant after the clot has formed.
Anticoagulants in the blood, like heparin and antithrombin, normally prevent spontaneous coagulation. In the absence of these anticoagulants, as would be the case in the tube without anticoagulant, the blood will follow the steps of hemostasis to form a thrombus, and then, with the cells trapped in the fibrin mesh, serum is left behind. In clinical practice, serum is used for various laboratory tests that do not require clotting factors, which would be present in plasma but are not needed for these specific analyses.