What is the liquid part of blood known as?

The liquid part of blood is known as plasma. Plasma is a yellowish fluid that makes up about 55% of total blood volume and plays a crucial role in transporting nutrients, hormones, and proteins throughout the body. It also helps in regulating body temperature and maintaining pH balance. Plasma contains not only water but also dissolved salts, enzymes, antibodies, and waste products.

Understanding plasma is essential in the context of blood's overall function, as it serves as the medium where various components of blood, such as red blood cells, white blood cells, and platelets, are suspended. Other choices, while related to components of blood, do not correctly define its liquid portion. For example, platelets are cell fragments involved in blood clotting, serum is the fluid that remains after blood has clotted and is free of clotting factors, and hemoglobin is a protein in red blood cells responsible for oxygen transport.