Final answer:
Fibrinogen is a protein in plasma that, along with platelets and coagulation factors, forms blood clots to stop excessive bleeding during injuries.
Step-by-step explanation:
The protein in plasma that forms blood clots and stops excessive bleeding during tissue or vascular injury is fibrinogen. When bleeding occurs, platelets and coagulation factors work together to form a blood clot. Platelets adhere to the site of injury, releasing contents that activate other platelets and coagulation factors. These factors convert fibrinogen into fibrin, resulting in a clot that halts further blood loss and begins the healing process.