Which component is defined as the liquid portion of unclotted blood?

Plasma is the correct answer because it refers specifically to the liquid portion of unclotted blood. Plasma makes up about 55% of total blood volume and is composed of water, electrolytes, nutrients, hormones, and waste products, along with proteins that are crucial for various bodily functions.

When blood is drawn and allowed to clot, the solid components (like red and white blood cells, and platelets) settle at the bottom, leaving the liquid portion, known as serum. However, serum is derived from blood that has already been allowed to clot and thus does not encompass the full range of components found in plasma, such as clotting factors.

Platelets are not a liquid component but are rather cellular fragments involved in the clotting process. Clotting factors also refer to proteins involved in the blood coagulation process and are found in plasma, but they are not a standalone liquid portion of blood. Therefore, plasma is distinctly defined as the liquid part of unclotted blood, making it the correct choice.