Which liquid part of blood makes up about 55% of total blood volume?

• A. Serum
• B. Plasma
• C. Platelets
• D. Red blood cells

Answer: (B)

Plasma is the liquid component of blood that makes up about 55% of its volume. It’s mostly water and carries key substances like proteins (albumin, globulins, and fibrinogen), electrolytes, nutrients, hormones, wastes, and clotting factors. This fluid serves as the transport medium for these components throughout the body. After blood clots, the liquid left is serum, which lacks fibrinogen and other clotting factors, so it’s not the same as plasma. Platelets and red blood cells are formed elements, not the liquid portion.