Which component primarily comprises the transport medium of blood?

The correct answer is plasma, as it acts as the main transport medium of blood, serving several crucial functions. Plasma is a yellowish liquid component that makes up about 55% of total blood volume. It is primarily composed of water, which constitutes about 90% of its content, along with various dissolved substances such as electrolytes, nutrients, hormones, proteins, and waste products.

The role of plasma is vital; it carries red and white blood cells, platelets, nutrients from digestion, metabolic waste for excretion, and hormones to different parts of the body. It helps maintain blood pressure and volume and plays a key role in immune responses and thermoregulation.

While cells, proteins, and salts play important roles in blood function, they do not act as the main transport medium. Red and white blood cells are responsible for oxygen transport and immune function, proteins such as albumin contribute to osmotic balance and transport, and salts help maintain electrolyte balance, but it is the plasma that serves as the fluid matrix allowing for the movement and transportation of these elements throughout the body.