Exchange Surfaces Practice Test

Plasma, which is the liquid component of blood, is primarily composed of water, making it a crucial element of the body’s circulatory system. Approximately 90-92% of plasma is water, which serves as a solvent for various substances, including nutrients, hormones, and waste products. This high water content is essential for maintaining blood volume and facilitating the transport of materials throughout the body.

While proteins, electrolytes, and cells are important components of plasma, their proportions are significantly smaller. Proteins, such as albumin and globulins, contribute to functions like maintaining osmotic pressure and immune responses, but they make up about 6-8% of plasma. Electrolytes (such as sodium, potassium, and chloride) are vital for nerve function and muscle contraction, but they are also present in much lower concentrations compared to water. The cellular components (red blood cells, white blood cells, and platelets) are suspended in plasma but represent a fraction of the total volume.

Understanding the composition of plasma underscores the importance of water in maintaining the structural and functional integrity of the circulatory system, which highlights why water is identified as the primary component in plasma.