Serum is the liquid that remains after blood has been allowed to clot.

• A. True
• B. False
• C. It is the liquid that remains after separating plasma
• D. It is the solid portion

Answer: (A)

The main idea is that serum is the liquid portion of clotted blood. When blood is allowed to clot, fibrin and other clotting factors form a solid clot, trapping cells. After removing that clot, the remaining liquid is serum—not plasma—because the clotting factors (like fibrinogen) have been used up in forming the clot. Therefore the statement is true. The liquid left after clotting is not the liquid after separating plasma, since plasma is the liquid portion before clotting; the solid clot remains when separating plasma, and serum is the liquid that stays after the clot is removed. The solid portion is not serum.