What is the primary function of white blood cells?

The primary function of white blood cells is to fight infection. These cells are a crucial component of the immune system, responsible for identifying and eliminating pathogens such as bacteria, viruses, and parasites. They achieve this through various mechanisms, including producing antibodies, engulfing and digesting foreign invaders, and coordinating the immune response. The presence of white blood cells is essential for maintaining the body's defense against infectious diseases and ensuring overall health.

The other options represent different functions of various components of blood. For instance, clotting is primarily the function of platelets, which help prevent excessive bleeding. The transport of blood back to the heart is primarily handled by veins, while the liquid portion of blood, known as plasma, contains water, electrolytes, proteins, and waste products but does not have a direct role in fighting infections like white blood cells do. Understanding the specific roles of these components helps clarify the critical functions that white blood cells perform in the body.