In the context of blood composition, serum is best described as blood plasma minus its what?

• A. Clotting proteins (especially fibrinogen)
• B. Platelets (thrombocytes)
• C. Leukocytes (white blood cells)
• D. Erythrocytes (red blood cells)

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the components of blood. Blood consists of plasma (the liquid part) and formed elements, which include erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (thrombocytes).
2. Step 2: Define blood plasma. Plasma is the clear, straw-colored liquid portion of blood that contains water, electrolytes, nutrients, hormones, waste products, and proteins, including clotting proteins like fibrinogen.
3. Step 3: Define serum. Serum is the fluid that remains after blood has clotted and the clot has been removed. It is essentially plasma without the clotting proteins.
4. Step 4: Identify what is removed from plasma to get serum. During clotting, clotting proteins such as fibrinogen are used up to form the clot, so serum lacks these clotting proteins.
5. Step 5: Conclude that serum is blood plasma minus its clotting proteins (especially fibrinogen), while other components like platelets, leukocytes, and erythrocytes are part of the formed elements and not present in plasma or serum.