What is the liquid portion of the blood known as?

The liquid portion of the blood is known as plasma. Plasma serves several critical functions in the body; it transports nutrients, hormones, and proteins to the parts of the body that need them. Additionally, plasma plays a key role in maintaining blood pressure and volume, and it is essential for the proper functioning of the immune system.

While hemoglobin refers to the protein in red blood cells that carries oxygen, it is not a liquid component of blood. Serum is sometimes confused with plasma, but it is actually the fluid that remains after blood has clotted, and therefore lacks clotting factors. Platelets are cell fragments involved in blood clotting, not a liquid component. Hence, plasma is the correct answer as it encompasses the variety of soluble components that circulate in the bloodstream.