Which Substance Must Be Present at All Times in the Blood

Question

Which substance must be present at all times in the blood for the blood to clot properly?
A) thrombin
B) fibrin
C) calcium
D) All of the above substances must be present at all times for the blood to clot properly.

Accepted Answer

Calcium is an essential component for the blood clotting process as it activates several enzymes and proteins involved in the coagulation cascade. Thrombin and fibrin are also important for blood clotting, but they are not always present in the blood at all times. Thrombin is produced during the coagulation cascade, while fibrin is the final product that forms a mesh-like clot over the injured blood vessel. Therefore, the best choice is C, as calcium needs to be present for the blood to clot properly.