Serum is the straw-colored liquid that remains after blood clots. Which description best defines serum?

• A. Clotting Factors
• B. Straw-Colored Liquid
• C. Platelets
• D. Red Blood Cells

Answer: (B)

Serum is the liquid portion of blood that remains after it clots. When blood clots, the clotting factors (like fibrinogen) are used up to form the clot, so the liquid that stays is the serum—it's pale straw-colored and lacks those clotting factors. This makes the description “Straw-Colored Liquid” the best fit for serum. The other components, such as platelets and red blood cells, are cellular elements that settle with the clot and are not part of the serum. Plasma, by contrast, includes clotting factors and fibrinogen because it’s obtained from blood that hasn’t clotted.