According to the American Red Cross, the liquid portion of the blood is called plasma. Made up of 92 percent water, plasma is responsible for transporting red and white blood cells along with platelets throughout the body.
The University of Rochester Medical Center states that blood is made mostly of plasma. Along with the blood cells, plasma transports vital nutrients, proteins and hormones to the body's cells, and in return, the cells deposit their waste into the plasma so that it can be removed from the body. To obtain plasma in its pure form, a process called plasmapheresis is performed after a blood donation, which separates the plasma from the blood cells and platelets.