MCQ Detailed View

Blood is a vital fluid in the human body that transports oxygen, nutrients, hormones, and waste products. It consists of plasma and cellular components (red blood cells, white blood cells, and platelets). Plasma is the liquid portion of blood that contains water, electrolytes, proteins, and other dissolved substances.

When blood is allowed to clot, certain proteins responsible for clotting are used up in the process. The fluid that remains after clotting is called serum. Thus, serum is blood plasma minus its clotting proteins, primarily fibrinogen and other clotting factors. This is why serum does not clot, as the proteins that enable clot formation have been removed or consumed.

Key differences between plasma and serum:

1. 
   

   Plasma: Contains clotting proteins (like fibrinogen), water, salts, glucose, hormones, and other proteins such as albumins and globulins.

   
   


2. 
   

   Serum: Contains everything plasma has except clotting proteins. It still contains antibodies, electrolytes, and other essential proteins but cannot form clots.

   
   

Calcium ions, another important factor in blood clotting, are not the defining difference between plasma and serum. Globulins, which are immune system proteins, are still present in serum.

Serum is widely used in diagnostic tests, medical research, and the production of vaccines because it allows scientists and doctors to study the components of blood without interference from clotting factors.

Hence, the correct answer is clotting proteins, as serum is simply plasma with these clotting proteins removed or depleted after the clotting process has occurred.