What are the main components of plasma?

• A. Water and dissolved substances
• B. Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets
• C. Plasma proteins
• D. Antibodies

Answer: (B)

Plasma is the liquid portion of blood that acts as the transport medium for cells and dissolved substances. It is composed mostly of water, which suspends a variety of dissolved substances such as electrolytes, nutrients, gases, and waste products. In addition to water and solutes, plasma contains plasma proteins—albumin, globulins, and fibrinogen—that support functions like maintaining osmotic pressure and blood clotting. Immunoglobulins (antibodies) are a type of plasma protein important for immune defense.

The cells listed—red blood cells, white blood cells, and platelets—are not part of plasma itself. They are the formed elements that circulate within plasma but constitute the cellular component, not the liquid plasma component. So the main component of plasma is the watery fluid with dissolved substances, and among the dissolved components, plasma proteins (including antibodies) play key roles.