What constitutes approximately 45% of the makeup of blood?

The correct answer is that formed elements constitute approximately 45% of the makeup of blood. Formed elements include red blood cells, white blood cells, and platelets. Red blood cells are the most abundant type of formed element and are essential for transporting oxygen throughout the body. White blood cells play a crucial role in the immune response, while platelets are vital for blood clotting.

In contrast, plasma, which is the liquid component of blood, accounts for about 55% of blood volume. Water, a major component of plasma, makes up around 90-92% of plasma itself but is not a standalone component of blood. Whole blood refers to the complete composition of blood, including both the plasma and the formed elements, and therefore does not specifically represent the percentage of formed elements alone.