What is the primary role of white blood cells in the blood?

White blood cells, also known as leukocytes, play a crucial role in the immune system by defending the body against infections and diseases. Their primary function is to identify and eliminate pathogens such as bacteria, viruses, and fungi that can cause illness. White blood cells are involved in various immune responses, including the production of antibodies and the activation of other parts of the immune system to target and destroy invaders.

When an infection occurs, the body signals an increase in the production and release of white blood cells, which then migrate to the site of infection to combat the pathogens. This defensive mechanism is essential for maintaining health and ensuring the body can respond effectively to infections.

The other options, while they represent important functions within the blood, do not pertain to the primary role of white blood cells. Red blood cells are responsible for transporting oxygen, platelets are primarily involved in clotting, and plasma carries nutrients. Thus, the unique and vital function of white blood cells in fighting infection is what sets them apart and makes this option the correct choice.