SAT Biology Subject Test Practice Questions

Answer: A, Plasma. Plasma, which is mostly water, makes up about 55% of the total blood volume, exceeding all other components of blood combined.

Main Takeaway: Plasma, which is mostly water, is the liquid that red and white blood cells are suspended in within blood. Plasma contains inorganic ions which are important for body function and homeostasis. While red blood cells transport oxygen and white blood cells serve as the body’s defense system, it is plasma that transports essential nutrients and materials throughout the body.