Which protein is found in plasma?

Fibrinogen is a key protein found in plasma that plays a vital role in blood clotting. It is produced by the liver and is one of the main components of the coagulation process. When a blood vessel is injured, fibrinogen is converted into fibrin, which forms a mesh that helps seal wounds and stops bleeding. This function is crucial to maintaining hemostasis, the process that prevents and stops bleeding.

The other components listed, such as hemoglobin, are not found in plasma. Hemoglobin is primarily located within red blood cells and is responsible for transporting oxygen throughout the body. White blood cells and red blood cells themselves are not considered plasma proteins; rather, they are cellular components of blood that serve different functions in the immune response and oxygen transport, respectively. Thus, fibrinogen stands out as the correct answer in the context of proteins specifically found in plasma.