Plasma is primarily composed of water. Which option best describes its composition?

• A. Plasma proteins
• B. Water
• C. Lipids
• D. Cells

Answer: (B)

Plasma is the liquid part of blood that acts as a transport medium for everything dissolved and suspended in it. The dominant component is water, which makes plasma a clear, watery fluid and provides the solvent for salts, nutrients, hormones, wastes, and many other substances. Plasma proteins are important for functions like maintaining blood volume and clotting, and they are present in substantial amounts, but they do not exceed the amount of water. Lipids are carried in plasma as part of lipoprotein complexes, but they make up only a small portion of plasma’s composition. The cells—red and white blood cells and platelets—are not part of plasma; they’re the formed elements that float in it. So describing plasma as primarily water is the best answer.