In the context of blood composition, what is serum?

• A. The liquid portion of blood after clotting has occurred; it is plasma without clotting factors (e.g., fibrinogen).
• B. The cellular component of blood composed primarily of erythrocytes, leukocytes, and platelets.
• C. The liquid portion of blood that still contains clotting factors and is obtained when blood is prevented from clotting.
• D. A protein in red blood cells that binds and transports oxygen, giving blood its red color.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the components of blood, which include the cellular elements (erythrocytes, leukocytes, and platelets) and the liquid portion (plasma).
2. Step 2: Recognize that plasma is the liquid part of blood that contains water, electrolytes, nutrients, hormones, proteins, and clotting factors such as fibrinogen.
3. Step 3: Learn that when blood is allowed to clot, the clotting factors are used up in forming the clot, and the remaining liquid is called serum.
4. Step 4: Define serum as the liquid portion of blood after clotting has occurred, meaning it is plasma without the clotting factors like fibrinogen.
5. Step 5: Differentiate serum from plasma by noting that plasma contains clotting factors, whereas serum does not, and also distinguish serum from the cellular components and hemoglobin.